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高剂量维生素疗法刺激变体酶,其具有降低的辅酶结合亲和力(增加的Km):与遗传病和...

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发表于 2019-9-3 13:57:02 | 显示全部楼层 |阅读模式
High-dose vitamin therapy stimulates variant enzymes with decreased coenzyme binding affinity (increased Km): relevance to genetic disease and polymorphisms1–3
高剂量维生素疗法刺激变体酶,其具有降低的辅酶结合亲和力(增加的Km):与遗传病和多态性的相关性
Bruce N Ames, Ilan Elson-Schwab, and Eli A Silver
ABSTRACT
As many as one-third of mutations in a gene result in the corresponding enzyme having an increased Michaelis constant, or Km, (decreased binding affinity) for a coenzyme, resulting in a lower rate of reaction. About 50 human genetic diseases due to defective enzymes can be remedied or ameliorated by the administration of high doses of the vitamin component of the corresponding coenzyme, which at least partially restores enzymatic activity. Several single-nucleotide polymorphisms, in which the variant amino acid reduces coenzyme binding and thus enzymatic activity, are likely to be remediable by raising cellular concentrations of the cofactor through high-dose vitamin therapy. Some examples include the alanine-to-valine substitution at codon 222 (Ala222→Val) [DNA: C-to-T substitution at nucleo-tide 677 (677C→T)] in methylenetetrahydrofolate reductase (NADPH) and the cofactor FAD (in relation to cardiovascular disease, migraines, and rages), the Pro 187→Ser (DNA: 609C→T) mutation in NAD(P):quinone oxidoreductase 1 [NAD(P)H dehy-drogenase (quinone)] and FAD (in relation to cancer), the Ala44→Gly (DNA: 131C→G) mutation in glucose-6-phosphate 1-dehydrogenase and NADP (in relation to favism and hemolytic anemia), and the Glu487→Lys mutation (present in one-half of Asians) in aldehyde dehydrogenase (NAD+) and NAD (in relation to alcohol intolerance, Alzheimer disease, and cancer). Am J Clin Nutr 2002;75:616–58.

多达三分之一的基因突变导致相应酶的米氏常数增加,或KM,(降低结合亲和力)对辅酶,导致反应速率降低。大约50种由酶缺陷引起的人类遗传病可以通过使用相应辅酶的高剂量维生素组分来补救或改善,至少部分恢复了酶的活性。几个单核苷酸多态性,其中变异的氨基酸减少辅酶结合,从而降低酶活性,可以通过高剂量维生素治疗来提高细胞内辅助性因子的浓度。一些例子包括基码222丙氨酸对戊酸盐取代(Ala222→Val)[DNA: C-to-T substitution at 核苷酸 677 (677C T)C被T的替代],在亚甲基四氢叶酸还原酶(NADPH)和辅助因子FAD中,(这与心血管疾病、偏头痛和狂怒症),NAD(P)醌氧化还原酶1187位点脯氨酸→色氨酸(DNA:609C→T)基因突变,Ala44→Gly(dna:131c→G)突变于葡萄糖-6-磷酸脱氢酶和NADP(与嗜好和溶血性贫血有关),以及Glu487→Lys突变(存在于一半亚洲人)中的醛脱氢酶(NAD)和NAD(与酒精不耐受、阿尔茨海默病和癌症有关)。

KEY WORDS Genetic disease, therapeutic vitamin use, binding defect, favism, alcohol intolerance, autism, migraine headaches, single nucleotide polymorphisms, enzyme mutations, review

INTRODUCTION

High doses of vitamins are used to treat many inheritable human diseases. The molecular basis of disease arising from as many as one-third of the mutations in a gene is an increased Michaelis constant, or Km, (decreased binding affinity) of an enzyme for the vitamin-derived coenzyme or substrate, which in turn lowers the rate of the reaction. The Km is a measure of the binding affinity of an enzyme for its ligand (substrate or coenzyme) and is defined as the concentration of ligand required to fill one-half of the ligand binding sites. It is likely that therapeu-tic vitamin regimens increase intracellular ligand (cofactor) con-centrations, thus activating a defective enzyme; this alleviates the primary defect and remediates the disease. We show in this review that 50 human genetic diseases involving defective enzymes can be remedied by high concentrations of the vitamin component of the coenzyme, and that this therapeutic technique can be applied in several other cases, including polymorphisms associated with disease risks, for which molecular evidence suggests that a mutation affects a coenzyme binding site.

高剂量的维生素被用于治疗许多可遗传的人类疾病。由基因中三分之一的突变引起的疾病的分子基础是增加的Michaelis常数,或维生素衍生辅酶或底物酶的结合亲和力降低,这反过来又降低了反应的速度。KM是一种测定酶与配体(底物或辅酶)的结合亲和力的方法,它被定义为填充一半配体结合位点所需的配体浓度。很可能治疗维生素方案会增加细胞内配体(辅因子)的浓度,从而活化有缺陷的酶;这减轻了最初的缺陷,并补救了疾病。我们在这篇综述中指出,50种含有缺陷酶的人类遗传病可以通过高浓度辅酶的维生素组分来治疗,而且这种治疗技术是可行的。可以应用在其他几种情况下,包括与疾病风险相关的多态性,分子证据表明突变会影响辅酶结合位点。
The nutrients discussed in this review are pyridoxine (page 618); thiamine (page 625); riboflavin (page 627); niacin (page 632); biotin (page 637); cobalamin (page 638); folic acid (page 641); vitamin K (page 643); calciferol (page 645); tocopherol (page 645); tetrahydrobiopterin (page 646); S-adenosylmethion-ine (page 646); pantothenic acid (page 646); lipoic acid (page 647); carnitine (page 647); hormones, amino acids, and metals (page 648); and maxi B vitamins (page 649).

本综述中讨论的营养成分是吡多辛-维生素B6(第618页);硫胺素(第625页);核黄素(第627页);烟酸(第632页);生物素(第637页);钴胺(第638页);叶酸(第641页);维生素K(第643页);钙素(第645页);生育酚(第645页);四氢生物蝶呤(第645页)646;S-腺苷甲基-碱(第646页);泛酸(第646页);硫辛酸(第647页);肉碱(第647页);激素、氨基酸和金属(第648页);以及维生素A(第649页)。

The proportion of mutations in a disease gene that is responsive to high concentrations of a vitamin or substrate may be one-third or greater (1–3). Determining the true percentage from the literature is difficult because exact response rates in patients are not always reported and much of the literature deals only with individual case reports. The true percentages depend on several factors, such as the nature of the enzyme, the degree of enzyme loss that results in a particular phenotype, how much a small conformational change disrupts the binding site of the particular enzyme, whether the binding site is a hot spot for mutations, and whether dietary administration of the biochemical raises its concentration in the cell. From what is known of enzyme structure, it seems plausible that, in addition to direct changes in the amino acids at the coenzyme binding site, some mutations affect the conformation of the protein, thus causing an indirect change in the binding site.

对高浓度维生素或底物产生反应的疾病基因中突变的比例可能是三分之一或更多,从文献中确定真实的百分比是很困难的,因为病人的确切反应率并不总是被报告的,而且大部分文献只涉及个别病例报告。真正的百分比取决于几个因素,例如酶的性质,导致特定表型的酶丧失的程度,有多少小的构象变化破坏了特定酶的结合位点,是否结合位点是突变的热点,以及饮食中是否使用生化物质使它在细胞中的浓度升高。从已知的酶结构,似乎很有道理,除了辅酶结合位点上氨基酸的直接变化外,一些突变会影响蛋白质的构象,从而导致绑定站点的间接更改。

TABLE 1
Potentially vitamin-responsive polymorphisms1 潜在的对维生素治疗有反应的多态性

Enzyme and EC no.酶和EC号
Cofactor 辅因子
Nucleotide 核苷酸
Amino acid
氨基酸
Polymorphic frequency
多态频率
Region wherevariant is found 发现的区域
Characterization
特性描述

Methylenetetrahydrofolate reductase (NADPH)(1.5.1.20)
亚甲基四氢叶酸还原酶(NADPH)
FAD
黄素腺嘌呤二核苷酸,又称活性型维生素B2
677C→T
Ala222→Val
TT = 10–20
Worldwide
Human enzyme shows decreased affinity for FAD
人酶对FAD的亲和力降低

NAD(P):quinone oxidoreductase 1
NAD(P):醌氧化还原酶1
(1.6.99.2)

FAD
609C→T
Pro187→Ser
TT = 4–20
FAD affinity is lowered
FAD亲和力降低

Short-chain acyl-CoA dehydrogenase
短链酰基-CoA脱氢酶
(1.3.99.2)
FAD
625G→A
Gly209→Ser
AA + AG = 35
Control population of an SCAD study
SCAD研究的控制人群
Mutation may affect FAD interaction
突变可能影响FAD相互作用

Aldehyde dehydrogenase
醛脱氢酶(NAD+) (1.2.1.3)
NAD
烟酰胺腺嘌呤二核苷酸,简称:辅酶Ⅰ
Glu487→Lys
KK + EK = 50
Asians worldwide
全球亚洲人
Km (NAD) is increased 150-fold
Km(NAD)增加了150倍

Glucose-6-phosphate 1-dehydrogenase
葡萄糖-6-磷酸1-脱氢酶
(1.1.1.49)
NADP
烟酰胺腺嘌呤二核苷酸磷酸,辅酶II
131C→G
Ala44→Gly
G = 112
Rural south India
印度南部农村
Km (NADP) is increased 5-fold
Km(NADP)增加了5倍

Methionine synthase
蛋氨酸合酶
(2.1.1.13)
AdoCbl 腺苷钴胺素
2756A→G
Asp919→Gly
G = 152
Control population of an MS study
MS研究的控制种群
Mutation is in the AdoCbl binding site
突变在AdoCbl结合位点上

Folylpoly-γ-glutamate carboxypeptidase (3.4.19.9)
Folylpoly--glutamates (dietary
folates)
1561C→T
His475→Tyr
HY = 7.7 YY = 0.2
Control populationof a dementia study
痴呆研究的控制人群
Enzyme activity is lowered 53%
酶活性降低53%

1 AdoCbl, adenosylcobalamin; E, glutamate; H, histidine; K, lysine; K
m, Michaelis constant; MS, methionine synthase; SCAD, short-chain acyl-CoA dehy-
drogenase; Y, tyrosine.
2 Allelic frequencies.

An alternate form of a gene present in > 1% of the population is called a polymorphism. Some polymorphisms that are associated with a phenotype have been shown to alter cofactor binding and affect a large percentage of the population (see Table 1 for a list of the allelic frequencies of the polymorphisms dis-cussed in this review). Our analysis of metabolic disease that affects cofactor binding, particularly as a result of polymorphic mutations, may present a novel rationale for high-dose vitamin therapy, perhaps hundreds of times the normal dietary reference intake (DRI) in some cases. This area should interest the entire health community because of the considerable percentage of the population affected by polymorphisms, many of which may have outlived their genetic usefulness. The setting of a DRI may become more complicated if a sizable percentage of the popula-tion in fact has a higher B-vitamin requirement because of a polymorphism. It seems likely that the examples listed in Table 1 will represent the beginning of a much longer list as genomics advances and awareness of remediable Km mutants increases.

在超过1%的种群中存在的另一种基因形式称之为多态性。一些与表型相关的多态性已经被证明改变了辅助因子的结合,并影响了很大比例的群体。(本综述中讨论的多态性的等位基因频率列表见表1)。我们对影响辅助因子结合的代谢疾病的分析,特别是由于多态突变,可能为高剂量维生素治疗提供了一个新的理论基础,在某些情况下可能是正常饮食参考摄入量(DRI)的数百倍。这一领域应该引起整个卫生界的兴趣,因为受多态性影响的人口比例很大,其中许多可能已经失去了遗传效用。如果相当大比例的人群由于多态性而需要更高的维生素B,那么DRI的设定可能会变得更加复杂。表1中列出的例子很可能代表着随着基因组学的进步和对可补救的KM突变体的认识的提高,一个更长的列表的开始。

It also seems plausible that for each example of a genetic disease or polymorphism clearly involving derangement of metabolism, multiple forms of the disease exist that reflect slight increases in the enzyme Km but that are not commonly thought of as genetic diseases. It seems likely that, as the generality of this phenomenon is appreciated, this approach will be found to be effective on a wider scale and with a larger variety of enzyme substrates and cofactors. The administration of high doses of vitamins may reverse, at least partially, many more genetic dis-eases than those described here [see Online Mendelian Inheri-tance in Man (OMIM) (4) for extensive, referenced reports on human genetic diseases]. To facilitate the collection and organi-zation of similar data, we have created a forum on the Internet (www.KmMutants.org; 5) that will house dialogues on the data and ideas brought forth in this review; investigators in relevant disciplines are encouraged to correct or add to these discussions.

似乎也有道理,对于每一个明显涉及新陈代谢紊乱的遗传病或多态,这种疾病的多种形式反映了酶Km的轻微增加,但它们通常不被认为是遗传病。很有可能,由于这一现象的普遍性受到赞赏,这种方法将在更广泛的范围内被发现是有效的并且含有更多的酶底物和辅助因子。服用高剂量维生素可能会逆转,至少在一定程度上,更多的遗传疾病比这里描述的要简单得多。[关于人类遗传疾病的广泛参考报告,请参阅在线Mendelian Inheri-in Man(OMIM)(4)]。为方便收集和组织类似数据,我们在因特网上建立了一个论坛(www.KmMutants.org;5)这将包括关于本次审查中提出的数据和想法的对话;鼓励相关学科的调查人员纠正或补充这些讨论。


There are 40 000 human genes. Of the 3870 enzymes catalogued in the ENZYME database (6), 860 (22%) use a cofactor. Any cofactor used by many enzymes is of particular interest, such as the 8 vitamin-derived coenzymes discussed in this review. Although high-dose vitamin remediation seems to be routinely tried for diseases involving enzymes dependent on pyridoxal-P (PLP) and thiamine pyrophosphate (TPP), some of the vitamins, such as riboflavin, pantothenate, folate, and niacin, deserve more attention. Thus, www.KmMutants.org is also intended for the input of physicians, who may examine the benefits of high-dose multivitamin treatment (see the section on maxi B vitamins) for mental or metabolic disorders of unknown cause or report side effects of vitamin treatment. Provided safe dosages are used (Table 2), there is potentially much benefit and possibly little harm in trying high-dose nutrient therapy because of the nominal cost, ease of applica-tion, and low level of risk. Most of the vitamins discussed here appear safe in relatively high doses because the body can discard excess.

人类有40000个基因,在酶数据库中编目的3870种酶中(6),860(22%)的酶会使用辅助因子。许多酶所使用的任何辅酶都是特别令人感兴趣的,例如在本综述中讨论的8种维生素衍生辅酶。尽管高剂量的维生素治疗似乎经常被用于治疗疾病,如涉及依赖于吡啶-P(PLP)和焦磷酸硫胺(TPP)的酶。一些维生素,如核黄素、泛酸、叶酸和烟酸,值得更多的关注。因此,www.kmMutants.org也是供医生参考的,世卫组织可能检查高剂量复合维生素治疗(见复合维生素B族一栏)对未知原因的精神或代谢紊乱的益处,或报告维生素治疗的副作用。如果使用安全剂量(表2),尝试高剂量营养疗法有潜在的好处和可能的小危害,因为名义成本,容易使用,低风险水平。这里讨论的大多数维生素在相对高剂量的情况下似乎是安全的,因为身体可以丢弃过量的维生素。

Therapeutic remediation is contingent on increasing intracellular vitamin and cofactor concentrations; therefore, we present some data on plasma and tissue concentrations of coenzymes after the feeding of various amounts of vitamins (such informa-tion is sparse for some vitamins, especially at high doses). Data on plasma concentrations of amino acids after the administration of these metabolites would be desirable as well. Metals such as Mg2+, Ca2+, Zn2+, Fe2+, and K+ are used by many enzymes, but the increases in concentration obtainable may be small because of toxicity limitations and physiologic regulation. For example, zinc is a cofactor for > 300 proteins, but the human Zn2+ requirement is 10 mg/d and symptoms of toxicity can appear at 100 mg/d (10). Ascorbate concentrations are tightly regulated in young men and women and there is an upper limit on steady state plasma ascorbate concentrations of 80 mol/L (11, 12). At the end of each vitamin section, we discuss the toxicity of the vitamin as well as data on raising tissue concentrations. Note that some reports discussed below did not ascertain the minimal necessary therapeutic level of treatment, but instead used high doses that were thought would produce the desired effect. This treat-ment strategy is obviously not feasible with all nutrients (because of possible toxicity). Additionally, it is likely that not all administered vitamin is absorbed at very high doses (see the discussion of tissue concentrations and toxicity in the section on riboflavin). In an ideal situation, the lowest adequate therapeutic dosage would be elucidated and used.

治疗补救取决于增加细胞内维生素和辅助因子的浓度;因此,我们给出了一些数据,说明摄入不同量维生素后血浆和组织中辅酶的浓度(这种信息对于某些维生素来说是稀疏的),特别是在高剂量时)。服用这些代谢物后血浆中氨基酸浓度的数据也是可取的。诸如Mg2,Ca2,Zn2,Fe2,K等金属被许多酶所使用,但由于毒性限制和生理调节,可获得的浓度增加可能较小。例如,锌是超过300个蛋白质的辅助因子,但人体锌的需要量为10毫克/天,毒性症状可在100毫克/天(10)出现。抗坏血酸的浓度在年轻的男性和女性中受到严格的调节,稳态血浆抗坏血酸浓度的上限为80 mol/L。在每个维生素部分的末尾,我们讨论维生素的毒性以及提高组织浓度的数据。请注意,下面讨论的一些报告没有确定治疗的最低必要治疗水平,而是使用了被认为会产生预期效果的高剂量。这种治疗策略显然是不可行的,所有的营养(因为可能的毒性)。此外,并非所有服用的维生素都是在很高剂量下被吸收的(见关于核黄素一节中关于组织浓度和毒性的讨论)。在理想的情况下离子,最低的适当治疗剂量将被阐明和使用。

TABLE 2
Dietary reference intakes (DRIs), tolerable upper intake levels (ULs), and mega-doses of nutrients discussed in this review

本综述讨论了膳食参考摄入量(DRIs)、可耐受的高摄入量(ULs)和高剂量营养素。


Nutrient
DRI  1
UL  2
Mega-dose   大剂量 3
Pyridoxine (vitamin B-6)
1.3 mg
100 mg
1000 mg
Thiamine (vitamin B-1)
1.1 mg
[size=9.0000pt]—
1000 mg
Riboflavin (vitamin B-2)
1.1 mg
[size=9.0000pt]—
400 mg
Niacin (vitamin B-3)
14 mg
35 mg
2000 mg
Biotin (vitamin B-7)
30 [size=9.0000pt]μ[size=9.0000pt]g
[size=9.0000pt]—
100 000 [size=9.0000pt]μ[size=9.0000pt]g
Cobalamin (vitamin B-12)
2.4 [size=9.0000pt]μ[size=9.0000pt]g
[size=9.0000pt]—
1000 [size=9.0000pt]μg
Folic acid
400 [size=9.0000pt]μ[size=9.0000pt]g
1000 [size=9.0000pt]μ[size=9.0000pt]g
40 000 [size=9.0000pt]μ[size=9.0000pt]g
Vitamin K
90 [size=9.0000pt]μ[size=9.0000pt]g
[size=9.0000pt]—
45 000 [size=9.0000pt]μg
Calciferol (vitamin D)
5 [size=9.0000pt]μ[size=9.0000pt]g
50 [size=9.0000pt]μ[size=9.0000pt]g
5000 [size=9.0000pt]μg
Tocopherol (vitamin E)
15 mg
1000 mg
800 mg
Tetrahydrobiopterin四氢生物蝶呤
[size=9.0000pt]—
[size=9.0000pt]—
40 mg
S-AdenosylmethionineS-腺苷甲硫氨酸
[size=9.0000pt]—
[size=9.0000pt]—
800 mg
Pantothenic acid 泛酸
5 mg
[size=9.0000pt]—
150 m
Lipoic acid
[size=9.0000pt]—
[size=9.0000pt]—
300 mg
Carnitine 左旋肉碱
[size=9.0000pt]—
[size=9.0000pt]—
2000mg
Thyroid hormone 甲状腺激素
[size=9.0000pt]—
[size=9.0000pt]—
1.75 mg
Serine
[size=9.0000pt]—
[size=9.0000pt]—
500 mg · kg1 · d1
Glycine
[size=9.0000pt]—
[size=9.0000pt]—
200 mg · kg1 · d1
Zinc锌
8 mg
40 mg
Potassium钾
2000 mg
[size=9.0000pt]—
[size=9.0000pt]—
1 Daily values for female adults; values for males are similar. From ref-erences 7–9.女性成年人的日常价值观;男性的价值观相似。参考文献
2 The maximum daily nutrient intake that is likely to pose no risk of[size=9.0000pt] adverse effects. If no value is listed, either not enough data are available to establish a UL or no data are available.
每日最大营养素摄入量,可能不会带来不良影响的风险。如果没有列出值,则要么没有足够的数据来建立UL,要么没有可用的数据。
3 Upper doses used clinically as found in the literature; side effects were[size=9.0000pt] of less concern because of the disease severity but may accompany these mega-doses.
高剂量的临床使用,如在文献中发现;副作用是较少的关注,因为疾病的严重性,但可能伴随这些大剂量。


Nutritional interventions to improve health are likely to be a major benefit of the genomics era. Many coenzyme binding motifs have been characterized, and essential residues for binding have been elucidated. Structural data can be found at the beginning of many sections. It will soon be possible to identify the complete set of genes having cofactor binding sites and the polymorphisms that fall into these regions, with an end goal of using vitamins, and possibly amino acids, hormones, and minerals, to effect a metabolic “tune-up.”

改善健康的营养干预很可能是基因组时代的一大好处。许多辅酶结合单元已经被表征,并阐明了结合的基本残基。结构数据可以在许多章节的开头找到。很快就有可能识别出具有辅助因子结合位点的完整基因和属于这些区域的多态性,最终目标是使用维生素,可能还有氨基酸、激素和矿物质,来进行新陈代谢“调理”。

Support for some of the views discussed here can be found in the literature. It is clear that many individual researchers have recognized that high-dose vitamin treatment is effective in par-ticular diseases because a mutation affects the affinity of an enzyme for its coenzyme. In particular, Linus Pauling (13) hypothesized in his review entitled Orthomolecular Psychiatry that much mental disease may be due to insufficient concentrations of particular biochemicals in the brain as the result of an inadequate intake of particular micronutrients and that some brain dysfunction may be due to mutations that affect the Km of enzymes: “The still greater disadvantage of low reaction rate for a mutated enzyme with K[m] only 0.01 could be overcome by a 200-fold increase in substrate concentration to [S] = 400. This mechanism of action of gene mutation is only one of several that lead to disadvantageous manifestations that could be overcome by an increase, perhaps a great increase, in the concentration of a vital substance in the body. These considerations obviously suggest a rationale for megavitamin therapy.” More recently, high-dose pyridoxine therapy has been suggested as a treatment for improving dysphoric psychological states (eg, loneliness, anxiety, hostility, and depression) by stimulating the production of 2 pyridoxine-dependent neurotransmitters, serotonin and -aminobutyric acid (14).

对这里讨论的一些观点的支持可以在文献中找到。很明显,许多研究人员已经认识到,高剂量的维生素治疗对于寻常性疾病是有效的,因为突变会影响酶对辅酶的亲和力。尤其是Linus Pauling,他在题为“正分子精神病学”的评论中假设,许多精神疾病可能是由于大脑中特定生物化学物质浓度不足造成的。摄入特定微量营养素某些脑功能障碍可能是由于影响酶Km的突变:“K[m]突变酶的低反应率更大的缺点是只能克服0.01。底物浓度增加200倍,达到[S]=400.这种基因突变的作用机制只是导致不利表现的几种机制之一,这些不利的表现可以通过增加,也许是大幅度增加的浓度来克服。人体中的重要物质。这些考虑显然表明高剂量营养治疗的理论,最近,大剂量维生素B6被认为是一种改善焦虑症心理状态的治疗方法。(例如,孤独、焦虑、敌意和抑郁)通过刺激2种吡啶依赖性神经递质,5-羟色胺和GABA-氨基丁酸。

Although he does not discuss binding defects, Roger Williams (15), another pioneer in the field of biochemical nutrition, also recognized that higher doses of vitamins may be necessary to accommodate for what he calls biochemical individuality: “Indi-viduality in nutritional needs is the basis for the genetotrophic approach and for the belief that nutrition applied with due con-cern for individual genetic variations, which may be large, offers the solution to many baffling health problems. This certainly is close to the heart of applied biochemistry.” [Human genetic vari-ation appears greater than previously thought (16).] Williams’ conclusions suggest that genetic and thus biochemical individu-ality necessitates much nutritional individuality. This is especially relevant in the dawning age of genomics, in which it will someday become routine to screen individuals for polymorphisms and thus treat persons more efficaciously by genotype, rather than just by phenotype.

虽然他没有讨论绑定缺陷,罗杰威廉姆斯,另一个在生物化学营养学领域的先驱,也认识到高剂量的维生素可能是必要的,以适应他称之为生化个性:“营养需求的内在性是基因营养方法的基础,也是认为营养与个体遗传变异相一致的基础,而这些变异可能是巨大的。”解决了许多令人困惑的健康问题。这无疑是应用生物化学的核心。“[人类遗传变异似乎比先前想象的要大(16)。,Williams的结论表明,遗传和生物化学的不可分割性需要大量的个性化营养。在基因组学的曙光时代,这一点尤其重要。在这个时代,筛查个体的多态性从而以基因型更有效地对待人将成为惯例,而不仅仅是表型。

It also appears that, during aging, oxidation deforms many proteins, thereby decreasing their affinity for their substrates or coenzymes (17). Mechanisms of protein deformation include direct protein oxidation, adduction of aldehydes from lipid per-oxidation, and, in the case of membrane proteins, decreases in fluidity of oxidized membranes. This oxidative decay is particu-larly acute in mitochondria (18–20). Thus, feeding high amounts of several mitochondrial biochemicals may reverse some of the decay of aging (17, 21–26). Fourteen genetic diseases due to defective mitochondrial proteins are discussed in this review.

它也会出现,在老化过程中,氧化会使许多蛋白质变形,从而降低它们对底物或辅酶的亲和力。蛋白质变形的机制包括蛋白质直接氧化、脂质每次氧化中醛的加合以及膜蛋白流动性的降低。。这种氧化衰变在线粒体中尤为剧烈。因此,摄入大量的线粒体生物化学物质可能会逆转衰老的某些衰变。本文就线粒体蛋白缺陷引起的14种遗传病进行了综述。

The impetus for this review arose while teaching an undergraduate laboratory course in which the students isolated bacterial mutants that grew on a complex medium but not on a minimal medium and characterized the defective gene and pathway. An appreciable percentage of mutant phenotypes could be explained by an increased Km (decreased affinity) of an enzyme, which could then be remedied by higher concentrations of the coenzyme or substrate (27).

这一审查的动力是在教授一门本科生实验室课程时产生的,在这门课程中,学生们分离出了细菌突变体。它生长在复杂的培养基上,但不是在最低限度的培养基上生长,并且具有缺陷基因和通路的特征。一个明显的突变表型的百分比可以解释为一种酶的Km增加(亲和力降低),然后可以用较高浓度的辅酶或底物来补救。

PYRIDOXINE (VITAMIN B-6) 吡多辛(维生素B-6)

The DRI for vitamin B-6 is 1.3 mg/d for adults (7). In the liver, pyridoxine and pyridoxal (an oxidized form of pyridoxine) are phosphorylated by pyridoxal kinase to form pyridoxine-P and PLP, the active cofactor form. Pyridoxine-P is oxidized to PLP by pyridoxine oxidase (7). PLP is utilized by 112 (3%) of the 3870 enzymes catalogued in the ENZYME database (6). The cofactor forms a covalent linkage (Schiff base) with a lysyl residue in the enzyme. This internal aldimine (enzyme-PLP) is converted to an external aldimine (substrate-PLP) when PLP is attacked by a substrate amino group. The PLP binding site has been elucidated for some enzymes (28) and may be useful for probing genomic sequences for homology. The PLP-requiring enzymes discussed in this section are summarized in Table 3.

维生素B-6的DRI为成年人1.3mg/d。在肝脏中,吡多星和吡多沙尔(嘧啶的氧化形式)被吡啶醛激酶磷酸化生成吡多辛-P以及PLP,活性辅助因子形式。吡啶多辛-P被吡啶多辛氧化酶氧化为PLP。在酶数据库中编目的3870种酶中,有112种(3%)使用了PLP。辅助因子形成共价键(Schiff base)在酶中残留了一种赖氨酸。这种内部醛亚胺(酶-PLP)被转化为外部胺 (substrate-PLP)当PLP被底物氨基攻击时。一些酶的PLP结合位点已经被阐明。可能有助于研究基因组序列的同源性。本节讨论的需要PLP的酶概述在表3中。

Ornithine aminotransferase: gyrate atrophy of the choroid and retina 鸟氨酸转氨酶:脉络膜和视网膜的旋转萎缩

Ornithine aminotransferase (OAT; ornithine–oxo-acid transam-inase) is a PLP-dependent mitochondrial matrix protein that catalyzes the breakdown of ornithine to -pyrroline-5-carboxylic acid, which is then converted into proline. Defects in OAT lead to gyrate atrophy of the choroid and retina, an autosomal recessive disease that affects persons of all ages (see OMIM 258870). The disease is characterized by slowly progressive chorioretinal degeneration leading to blindness. Ornithine accumulates 10- to 15-fold when the enzyme is defective and appears to be responsi-ble for much of the pathology of gyrate atrophy (29). In the pyridoxine responsive forms of the disease, for which doses ranged from 10 to 750 mg/d, it appears that the defective enzyme has a Km defect for PLP; ornithine accumulation is decreased when patients are given high doses of pyridoxine.

鸟氨酸转氨酶(OAT;鸟氨酸-氧-酸转运酶)是一种依赖plp的线粒体基质蛋白,催化鸟氨酸分解成吡咯啉-5-羧酸,然后转化成脯氨酸。OAT的缺陷导致脉络膜和视网膜的旋转萎缩,一种常染色体隐性疾病,影响所有年龄的人(见OMIM 258870)。这种疾病的特点是缓慢进展的脉络膜视网膜退化导致失明。鸟氨酸在酶有缺陷时会累积10至15倍,似乎对许多回转体萎缩的病理都有反应。这种疾病的吡多辛反应形式,其剂量范围为10至750毫克/天,该缺陷酶对PLP有KM缺陷,当给予大剂量吡多星时,鸟氨酸积累减少。

The OAT activity in fibroblast extracts of a pyridoxine-respon-sive patient with the alanine-to-valine substitution at codon 222 (Ala226→Val) increased from 9 to 44 nmol product · mg1 · h1 when the concentration of PLP in the assay was increased to 600 mol/L. The Km from the cell line of a second patient with the same Ala226→Val mutation was 122 mol/L (control Km: 6 mol/L). Similar to cells from the second patient, Chinese hamster cells expressing an OAT complementary DNA (cDNA) producing the Ala226→Val protein also exhibited increased OAT activity with the addition of pyridoxine (30).

Vitamin B-6–responsive and -nonresponsive patients with gyrate atrophy were shown to have different point mutations resulting in single amino acid changes in the mature enzyme (31). After incubation with 40 mol PLP/L, OAT activity increased substantially more in fibroblasts from carriers of the pyridoxine-responsive variant than in fibroblasts from control subjects and nonresponsive patients (32). These investigators concluded that “the greater increases in activity seen in pyridoxine-responsive cells when PLP was added to the assay suggest both that the holoenzyme content in these cells is decreased owing to low affinity and that PLP binding to the apoenzyme occurs at a higher concentration.”

In another study, 3 patients responded to oral vitamin B-6 (600–750 mg/d) with a decrease in serum ornithine and a return to normal of reduced concentrations of serum lysine. Lower doses of vitamin B-6 (18–30 mg/d) appeared to work just as well as the high doses (33).

In another study of 9 patients with gyrate atrophy (34), 4 patients responded to pyridoxine, which lowered serum ornithine by ≥50% in 3 cases. The Km (of OAT for PLP) was 23 mol/L in the con-trol subjects, 23 mol/L in the pyridoxine-nonresponsive patients, and 168 mol/L in the pyridoxine-responsive patients. This higher Km for pyridoxine-responsive patients could be explained by mutations in the binding site that severely reduce coenzyme affinity, whereas nonresponsive patients may harbor more severe mutations that affect a different area of the enzyme.

In a study of Japanese patients in which 1 of 7 patients (all with different mutations) responded to vitamin B-6, the pyridoxine-responsive mutation was found to be Thr181→Met, but the affin-ity for PLP was not measured (35). In another Japanese study, one patient (of 3) responded to vitamin B-6 (300–600 mg/d) with a 60% reduction in serum ornithine concentrations. OAT activity in the fibroblasts from this patient increased up to 25% of normal levels in the presence of 2000 mol PLP/L, although no signifi-cant improvement was observed in acuity or visual field. Thus, vitamin B-6 responsiveness may be due to a mutation in OAT that results in a high Km for PLP (36, 37). A Glu318→Lys muta-tion of the OAT gene was found in 3 heterozygous patients and 1 homozygous patient, all of whom were vitamin B-6-responsive according to previous in vivo and in vitro studies. Dose-dependent effects of the Glu318→Lys allele were observed in the homozy-gotes and heterozygotes in 1) OAT activity, 2) increase of OAT activity in the presence of PLP, and 3) apparent Km for PLP with these values approximately doubled in the homozygous individual compared with the heterozygotes. Thus, the highest residual level of OAT activity and mildness of clinical disease correlated directly with the higher number of the mutant Glu318→Lys allele found in the homozygous patient (38).

Many case reports of gyrate atrophy exist; as of 1995, pyri-doxine-responsiveness had been observed in 7 of the 150 total documented cases (7/150 = 5%) (39). Whether pyridoxine treat-ment was actually attempted in each of these cases is unclear. Thus the true response rate may be higher or lower than 5%.

Cystathionine -synthase: homocystinuria 胱硫醚合成酶:高胱氨酸尿

Cystathionine -synthase (CBS) of the transsulfuration pathway catalyzes the PLP-dependent condensation of homocysteine and serine to form cystathionine. Individuals carrying a defective form of this enzyme (see OMIM 236200) accumulate homocys-teine in the blood and urine and display a wide range of symp-toms that appear to be due to homocysteine toxicity, including mental retardation, vascular and skeletal problems, and optic lens dislocation. Barber and Spaeth (40) were the first to report pyridoxine-responsiveness with a complete return to normal of the patient’s methionine and homocysteine concentrations in plasma and urine. They speculated that “if the deficient enzymatic activity were due to decreased affinity of a defective apoenzyme for its cofactor, activity might be restored by increas-ng the intracellular concentration of pyridoxal phosphate” (40).

转硫途径的胱硫醚合成酶(Cbs)催化同型半胱氨酸与丝氨酸的PLP依赖缩合形成胱硫醚.携带有缺陷的这种酶的个体(见OMIM 236200)在血液和尿液中积累同型半胱氨酸,展示了大量的同型半胱氨酸毒性物质,包括智力迟钝,血管和骨骼问题,以及光学晶状体脱位。Barber和Spaeth(40岁)第一次报告了吡多星的反应性,患者血浆和尿液中的蛋氨酸和同型半胱氨酸浓度完全恢复到正常水平。他们推测“如果酶活性不足是由于有缺陷的载脂蛋白酶对其辅助因子的亲和力降低,可通过增加磷酸吡啶的胞内浓度来恢复细胞活性。

Kim and Rosenberg (41) showed that CBS activity was 5% of that of control subjects in pyridoxine-responsive homocystinuric patients, who had markedly elevated plasma and urinary concen-trations of methionine and homocystine. The mutant synthases had a 20-fold lower affinity for PLP. A 2- to 3-fold increase in the Km for homocysteine and serine was found in one vitamin B-6-responsive patient, although the Km for PLP was not meas-ured. The maximum reaction rate (Vmax) was also reduced. It was suggested that pharmacologic doses of pyridoxine led to increased cellular concentrations of PLP and increased enzymatic activity (41).

金和罗森伯格,吡多星反应高胱氨酸尿患者的cbs活性为对照组的5%。明显升高血浆和尿蛋氨酸和高晶体的浓度。突变型合成酶对PLP的亲和力低20倍.在一名维生素B-6应答患者中发现同型半胱氨酸和丝氨酸的Km增加了2至3倍,虽然PLP的知识管理是不合理的。最大反应速率(Vmax)也有所降低。结果表明,吡咯烷酮的药理学剂量可引起细胞内PLP浓度的增加和酶活性的提高。

One group showed cell lines from pyridoxine-responsive patients to have higher Km values for PLP (155, 145, 195, and 200 mol/L) than control values (52, 52, and 85 mol/L), whereas nonresponsive patients had the highest values (990 and 4000 mol/L). It was noted that, in general, about one-half of CBS-deficient patients respond to pyridoxine with a lowering of homocysteine and serine concentrations to normal (42). A 21-y-old pyridoxine-responsive individual had a 3- to 4-fold elevated apparent Km of CBS for PLP as measured in fibroblast extracts (43). An Ala114→Val substitution was present in this indi-vidual, which is only 5 residues away from the lysine residue, Lys119, that binds PLP. These investigators concluded that in vivo responsiveness in individuals with some residual CBS activity is related both to the affinity of the mutant aposynthase for PLP and to the capacity of cells to accumulate PLP (43).

有一组患者的细胞株对吡多辛酸有较高的km值。(155、145、195和200 mol/L)超过对照值(52、52和85 mol/L),而无反应的病人有最高值(990和4000 mol/L)。据指出,一般而言,大约一半cbs缺乏的患者对吡多辛有反应,同型半胱氨酸和丝氨酸浓度降低到正常水平。以成纤维细胞提取液测量,21岁的吡多星敏感个体的cbs表观km为成纤维细胞提取物的3至4倍。在此标记中存在Ala114→Val取代,该碱基距赖氨酸残基Lys 119只有5个残基,而赖氨酸残基与PLP结合。这些调查人员得出结论,在体内,具有某些cbs活性的个体的反应性与突变的PLP合酶的亲和力有关,也与细胞累积PLP的能力有关系

In one report (44), a G-to-A substitution at nucleotide 797 (797G→A; amino acid substitution: Arg266→Lys) was found in most pyridoxine-responsive patients. Seven of 12 patients were responsive to pyridoxine (40–900 mg/d), which greatly decreased total plasma homocysteine. Pyridoxine (50–1000 mg/d) markedly reduced homocysteine excretion in a group of pyridoxine-responsive patients: patient 1, 867 to 10 mol/d; patient 2, 1021 to 79 mol/d; patient 3, 15 mol/L (blood concentration) to undetectable concentrations; and patient 4, plasma amino acids reverted to normal (45). It appears that a missense mutation (Ile278→Thr) is common (41%) in pyridoxine-responsive patients and that patients who are responsive to pyridoxine usually have a milder clinical pheno-type than do nonresponsive patients.

在一份报告中,核苷酸797的G到A替换(797G A; 氨基酸置换:精氨酸266 -赖氨酸)在大多数对吡多星有反应的病人中被发现。12例患者中有7例对吡多辛有反应。(40-900毫克/日),这大大降低了血浆总同型半胱氨酸。吡啶多辛(50-1000 mg/d)明显减少了一组对吡多星有反应的患者的同型半胱氨酸排泄:病人1,867至10 mol/d;病人2,1021至79 mol/d;病人3,15 mol/L(血液浓度)无法检测到的浓度;病人4血浆氨基酸恢复正常,似乎是一种错误的突变(Ile278-苏氨酸)很常见(41%),对吡多辛有反应的患者和对吡多辛有反应的患者,其临床症状类型通常比无反应的患者要轻。

The idea that pyridoxine-responsive patients have an increased Km was supported in a review of the mechanism of pyridoxine-responsive disorders (46). A review of the CBS deficiencies (2) found 629 patients in the literature: 231 (37%) were vitamin B-6–responsive, 231 (37%) were vitamin B-6–nonresponsive, 67 (11%) were intermediate in response, and 100 (16%) had not been classified. A decade later, the field was reviewed again and it was suggested that dosages of pyridoxine of 500 mg/d for 2 y appear to be safe, but that 1000 mg/d should not be exceeded (47).

吡多星反应患者Km增加的观点在一项对吡多星反应障碍的机制的综述中得到了支持。对CBS缺陷的回顾(2)在文献中发现629名患者:231(37%)维生素B-6敏感,231(37%)维生素B-6-无反应,67(11%)为中间反应,100例(16%)未分类。十年后,人们再次回顾了这一领域,并认为500 mg/d的吡多辛剂量2y似乎是安全的,但不应超过1000毫克/日。

A database of mutations in CBS (48) lists and maps >100 patho-genic mutations (including >70 missense mutations) that span all 7 exons of the CBS gene. Although the Schiff-base forming lysine has been assigned to nucleotide 119 in exon 3, it is difficult to say which domains are responsible for PLP binding. Serine should be tested clinically in addition to pyridoxine for treating patients, with the use of homocysteine concentrations as a measure of efficacy, because the Km of CBS for serine was shown to be increased in several cases (41). Oral serine administration (500 mg·kg1 ·d1) raises serine concentrations in plasma and cerebrospinal fluid (49), although very high doses (1400 mg·kg1 ·d1) can result in adverse effects (50).

CBS基因突变数据库列出和地图>100个致病突变(包括>70个错义突变),跨越CBS基因的所有7个外显子。虽然形成赖氨酸的席夫碱被指定为外显子3中的核苷酸119,很难说哪些域负责PLP绑定。丝氨酸除了用于治疗病人外,还应进行临床试验,用同型半胱氨酸浓度作为疗效的衡量标准,因为CBS对丝氨酸的Km在一些情况下被证明是增加的(41,)口服丝氨酸(500 mg·Kg1·D1)提高血浆和脑脊液中丝氨酸浓度,虽然很高的剂量(1400毫克·千克·d1)会产生副作用

Vitamin B-6-therapy may be valuable in more than just severe homozygous CBS-deficient cases: heterozygous parents of CBS-deficient patients also have significantly increased homocysteine concentrations (51). Increased homocysteine is a risk factor for cardiovascular disease (52). Heterozygosity for CBS deficiency may be present in 1% or 2% of the population.

维生素B-6-治疗不仅对严重的纯合子cbs缺乏症很有价值:cbs缺乏患者的杂合子父母也显著增加了同型半胱氨酸浓度。同型半胱氨酸升高是心血管疾病的危险因素(52)。CBS缺失的杂合性可能存在于1%或2%的人群中。

TABLE 3
Enzymes that use a pyridoxal-P (PLP) cofactor 1使用吡啶-P(PLP)辅助因子1的酶

Defective enzyme and EC no. 酶缺陷和EC号。
Localization 位置
Reaction catalyzed 反应催化
Disease or condition
疾病或状况
OMIM no.
Inheritance
Ornithine aminotransferase (2.6.1.13)
鸟氨酸转氨酶
Mitochondrial
线粒体
Ornithine + -ketoglutarate → △-pyrroline-5-carboxylate + glutamate
Gyrate atrophy of choroid and retina,degrading sight to eventual blindness
脉络膜和视网膜旋转萎缩,视力下降,最终失明。
258870
Autosomal recessive
常染色体隐性
Cystathionine β-synthase (4.2.1.22)
胱硫醚β合成酶
Cytoplasmic
细胞质
Homocysteine + serine → cystathionine
Homocystinuria, opticlens dislocation,osteoporosis, skeletal abnormalities, and mental retardation
高胱氨酸尿,骨质疏松症,骨骼异常,智力迟钝,智力缺陷
236200
Autosomal recessive
常染色体隐性
Erythroid specific -aminolevulinic acid synthase (2.3.1.37)
红系特异性氨基乙酰丙酸合酶
Mitochondrial
线粒体
Glycine + succinyl-CoA → δ-aminolevulinicacid + CoA + CO2   
X-linked sideroblastic anemia
X-连锁铁粒细胞性贫血
301300
X-linked recessive
X连锁隐性
Kynureninase (3.7.1.3)
犬尿酸酶
Cytoplasmic
细胞质
(Hydroxy-)kynurenine + H2O → (hydroxy-) anthranilic acid + alanine
Mental retardation
智力迟钝,智力缺陷
236800
Autosomal recessive
Glutamic acid decarboxylase (4.1.1.15)
谷氨酸脱羧酶
Cytoplasmic
细胞质
Glutamic acid → GABA
Infantile seizures unresponsive to typical anticonvulsants
婴儿惊厥对典型抗惊厥药无反应
266100
Autosomal recessive
γ-Cystathionase (4.4.1.1)
Γ-胱硫醚酶
Cytoplasmic
细胞质
Cystathionine → cysteine + α-ketobutyrate
Mental retardation, convulsions, thrombocytopenia, nephrogenic diabetes
insipidus, and diabetes mellitus
智力低下,抽搐,血小板减少,肾源性糖尿病
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尿崩症与糖尿病
219500
Autosomal recessive
Alanine–glyoxylate aminotransferase (2.6.1.44)
丙氨酸-乙醛酸转氨酶
Peroxisomal
过氧化物酶病
Alanine + glyoxylate → pyruvate + glycine
Hyperoxaluria, kidney (calcium oxalate) deposits, and renal failure
高草酸尿、肾(草酸钙)沉积和肾功能衰竭
259900
259900
Aromatic-L-amino-acid decarboxylase (4.1.1.28)
芳香-L-氨基酸脱羧酶
Cytoplasmic
细胞质
L-DOPA → dopamine + CO2;5-hydroxytryptophan → serotonin + CO2
Serotonin and dopamine deficiency,developmental delay, hypotonia,
5-羟色胺和多巴胺缺乏,发育迟缓,低张力,
107930
Autosomal recessive
Housekeeping -aminolevulinic acid synthase (2.3.1.37)
Mitochondrial
线粒体
Glycine + succinyl-CoA → δ-aminolevulinic
acid + CoA + CO2
Sideroblastic anemia
铁粒幼细胞性贫血
125290
Autosomal recessive
β-Alanine--ketoglutarate transaminase (2.6.1.19)
β-丙氨酸-酮戊二酸转氨酶
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β-Alanine → malonic semialdehyde
Cohen syndrome, hypotonia, midchildhood obesity, mental deficiency, and facial,
科恩综合征,低肌无力,儿童中期肥胖,智力缺陷,面部,
216550
Autosomal recessive
Enzyme involved with neurotransmittermetabolism (?)  
与神经递质代谢有关的酶
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[size=9.0000pt]
Autism
209850
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1 DOPA, dihydroxyphenylalanine; GABA, -aminobutyric acid; OMIM, Online Mendelian Inheritance in Man (4).

Erythroid specific δ-aminolevulinic acid synthase: X-linked sideroblastic anemia 红系特异性,δ-氨基乙酰丙酸合酶:X-连锁铁粒母细胞贫血

Erythroid specific -aminolevulinic acid synthase (ALAS2; 5-aminolevulinate synthase), with its PLP cofactor, is located in the mitochondria of animal cells and catalyzes the condensation of glycine and succinyl-CoA to form -aminolevulinic acid, the first and rate-limiting step in the series of reactions that makes heme for incorporation into hemoglobin. Defects in ALAS2 are responsible for the most common inherited form of sideroblastic anemia, which is X-linked (see OMIM 301300). Because iron is transported to the mitochondria whether or not it is combined with heme, deficiencies in heme lead to iron deposits in erythroblast mitochondria and increased ringed sideroblasts in the marrow (53). About one-third of patients with sideroblastic anemia respond to pyridoxine (1), with doses ranging from 50 to 600 mg/d.

红系特异性氨基乙酰丙酸合酶(ALAS2;5-氨基乙酰丙酸合酶),它的PLP辅因子位于动物细胞的线粒体中,催化甘氨酸与琥珀酰辅酶A缩合生成氨基乙酰丙酸,血红素进入血红蛋白的一系列反应中的第一步和限速步骤。ALAS 2的缺陷是最常见的遗传性铁质母细胞贫血的原因,它是X链接的(参见OMIM 301300)。因为铁被转运到线粒体,不管它是否与血红素结合,血红素缺乏症导致红细胞线粒体铁沉积,骨髓成铁细胞增多。大约三分之一的铁质再生障碍性贫血患者对吡多辛(1)有反应,剂量范围为50至600毫克/天。

Three generations in a family originally described by Cooley in 1945 were found to have an ALAS2 gene with an A-to-C point mutation that results in an ALAS2 variant with reduced activation by PLP. The specific activity of the mutant enzyme was 26% of normal in the presence of 5 mol PLP/L. The PLP cofactor activated or stabilized the purified mutant enzyme in vitro, consistent with the pyridoxine-responsive anemia in affected patients. It was hypothesized that the mutation alters the local secondary struc-ture and possibly perturbs the overall conformation, thus decreas-ing stability, reducing the affinity for PLP, or both (54).

在1945年Cooley最初描述的一个家族中,有三代人被发现有一个带有A到C点突变的ALAS 2基因,导致ALAS 2变异体被PLP激活降低。在5 mol PLP/L的情况下,突变酶的活性是正常酶的活性的26%。PLP辅助因子激活或者在体外稳定纯化的突变酶,与受影响患者的吡多星反应性贫血相一致。据推测,突变改变了局部次级结构,可能扰乱了整体构象,从而降低了稳定性,降低了对plp的亲和力,或者两者兼而有之。

A point mutation (663G→A) in the ALAS2 gene of an 8-mo-old Japanese male led to pyridoxine-responsive sideroblastic anemia. The activity of the mutant enzyme (Arg204→Gln) expressed in vitro was 15% of that of the control; with the addition of PLP, the activity of the mutant enzyme increased to 35% (55).

一位8岁的日本男性ALAS 2基因的点突变(663G→A)导致了吡多星反应性铁质形成性贫血。在体外表达的突变酶arg 204→Gln的活性为对照的15%;随着pplp的加入,突变酶的活性提高到35%。

Among 6 other cases (1 patient and 5 kindreds), 4 had an amino acid substitution at a PLP binding site of ALAS2 that reduced the affinity of ALAS2 for its coenzyme (1, 54, 56–58). One of the ALAS2 mutations, Gly291→Ser, reduced enzyme activity to 10% of normal; enzymatic activity was increased with the addition of PLP in vitro (57). In another mutation, Thr388→Ser, activity was decreased to 50% of wild-type but was raised by pyridoxine sup-plementation (1). A mutation found in a highly conserved region of exon 9, Ile471→Asn, was found in a 30-y-old Chinese man with the pyridoxine-responsive form of XLSA (56). Prokaryotic expression of the normal and mutant cDNAs showed that the mutant construct had lower enzymatic activity than did the normal enzyme and required higher concentrations of PLP to achieve maximal activation. The amino acid substitution occurred in the exon containing the putative PLP binding site, which may account for the reduced ability of the enzyme to catalyze the formation of -aminolevulinic acid. Another study showed that a large number of probands have mutations in exon 9, the exon containing the PLP binding site (59). Furuyama et al (60) reported an ALAS2 mutation that results in 12% of normal ALAS activity, which increases to 25% in the presence of PLP.

其他6例(1例成人和5例儿童),4例在alas 2的plp结合位点上有一个氨基酸替换,从而降低了alas 2对其辅酶的亲和力。ALAS 2突变之一Gly 291→Ser使酶活性降至正常水平的10%;ALAS 2突变之一Gly 291→Ser使酶活性降至正常水平的10%;体外添加PLP可提高酶活性。在另一种突变中,Thr 388→Ser的活性下降到野生型的50%,但因吡多辛的补充而升高。在第9外显子ile 471→asn高度保守的区域发现了一个突变,该突变发生在一名30岁的中国人身上。正常和突变体cdna的原核表达表明,突变体的酶活性低于正常酶,需要较高浓度的plp才能达到最大酶活性。氨基酸替换发生在含有推测的PLP结合位点的外显子中,这可能是该酶催化生成-氨基乙酰丙酸的能力降低的原因之一。另一项研究表明,大量的先证者在外显子9上有突变,该外显子含有plp结合位点。Furuyama等人报道了一个ALAS 2突变,导致12%的正常AlAs活性,在PLP存在的情况下增加到25%。

A novel missense mutation in the ALAS2 gene, 1754A→G, in a patient with 53% ALAS activity had 20% activity when expressed in bacteria but 32% in the presence of PLP. Although the mutation, which results in the substitution of glycine for serine, lies outside of exon 9, it is possible that it induces a conformational change that may alter PLP binding to the protein (61). Other mutations located outside exon 9 have also been reported to influence PLP binding (53).

ALAS 2基因中一个新的错义突变,1754A→G在53%AlAs活性的患者中在细菌中表达时活性为20%,在PLP存在时为32%。虽然导致甘氨酸取代丝氨酸的突变,位于外显子9之外,它可能会引起构象改变,从而改变PLP与蛋白质的结合。外显子9外显子外的其他突变也被报道会影响plp的结合。

Two cases that appeared late in life have also been analyzed (58). A 77-y-old man and an 81-y-old woman with initial diagnoses of refractory anemia with ringed sideroblasts (which is typi-cally unresponsive to pyridoxine) were found to respond very well to pyridoxine (100 mg/d in the man and 600 mg/d in the woman); hemoglobin concentrations increased in both patients after treatment. The mutations Lys299→Gln and Ala172→Thr were found in the man and woman, respectively. The Ala172→Thr mutation resulted in decreased in vitro stability of bone marrow ALAS2 activity. ALAS2 from both patients showed marked thermolability. Addition of PLP in vitro stabi-lized the mutant enzymes, which is consistent with the observed in vivo response to pyridoxine. This late-onset form can be dis-tinguished from refractory anemia and ringed sideroblasts by microcytosis, pyridoxine responsiveness, and ALAS2 muta-tions. These findings emphasize the need to consider all elderly patients with microcytic sideroblastic anemia as candidates for ALAS2 defects, especially if pyridoxine-responsiveness is demonstrated. These investigators concluded, “A decline in PLP availability or metabolism may have precipitated the late onset of XLSA in these patients. An age-related decline in pyridoxine metabolism in combination with a reduced vitamin intake has been described in elderly populations” (58).

我们还分析了两例晚年出现的病例(58).一名77岁的男子和一名81岁的妇女,最初诊断为顽固性贫血伴铁质网。(这是典型的对吡多辛没有反应)对吡多辛有很好的反应(男性为100 mg/d,女性为600 mg/d);两位患者治疗后血红蛋白浓度均升高。在男性和女性中分别发现Lys 299→Gln突变和Ala172→Thr突变。Ala172THR突变导致骨髓ALAS 2活性在体外稳定性下降。两位患者的ALAS 2均表现出明显的热溶作用。PLP在体外稳定突变酶,与观察到的体内对吡多星的反应是一致的。这种晚发型可通过微细胞增生症、吡多辛反应性和ALAS 2的变化,从难治性贫血和铁质形成细胞中获得。这些发现强调,需要考虑所有老年患者的微细胞铁质母细胞贫血作为ALAS 2缺陷的候选,特别是在证明了吡多星反应性的情况下。这些调查人员得出结论,“PLP的有效性或新陈代谢的下降可能导致这些患者的XLSA的晚发。与年龄有关的吡多辛酸代谢下降与减少的维生素摄入已在老年人口中被描述为“

It appears that supplementation with glycine, as well as pyridoxine, may be beneficial in new patients and that supplementation with glycine may be beneficial in patients who do not respond to pyridoxine, because the Km for glycine may be affected in some ALAS mutations. For example, the Gly142→Cys con-structed mutant has a 4-fold increased Km for glycine (62). If a patient had such a mutation, increased plasma glycine concen-trations might increase ALAS activity. One report showed an increase in plasma and cerebrospinal fluid glycine after the administration of 200 mg · kg1 · d1 (49).

似乎补充了甘氨酸,与吡啶多辛一样,对新病人也有好处,而补充甘氨酸对那些对吡多辛没有反应的病人也可能是有益的,因为甘氨酸的Km可能在某些AlAs突变中受到影响。例如,gly 142→cys结构突变体对甘氨酸的作用增加了4倍。如果病人有这样的突变,血浆甘氨酸浓度的增加可能会增加AlAs的活性.一份报告显示注射200 mg·kg1·d1(49)后血浆和脑脊液甘氨酸含量增加。

Kynureninase: xanthurenic aciduria and mental retardation  犬尿酸酶:黄嘌呤酸尿与智力低下

Kynureninase, a PLP-requiring enzyme involved in tryptophan degradation, catalyzes the conversion of kynurenine and 3-hydroxykynurenine to anthranilic acid and 3-hydroxyanthranilic acid, respectively (see OMIM 236800). Mutations in the kynureninase gene cause mental retardation in children and an excessive urinary output of 3-hydroxykynurenine and kynurenine (and their metabolites, xanthurenic and kynurenic acids). The condition was normalized in 2 children with pyridoxine doses of ≤ 30 mg/d. Significantly decreased kynureninase activity in a liver biopsy sample was markedly increased with the addition of PLP, suggesting that a mutation caused a modification in the binding site of the coenzyme (63). A follow-up study confirmed that the defective enzyme was a Km mutant (64).(See the discussion of autism in this section.)

犬尿氨酸,一种需要PLP的酶参与色氨酸的降解,催化犬尿氨酸和3-羟基犬尿氨酸转化为氨基苯甲酸和3-羟基-2-基苯甲酸。犬尿氨酸酶基因变异导致儿童智力低下和3-羟基犬尿氨酸尿和犬尿氨酸尿症(和其他的代谢产物,黄尿酸尿,犬尿喹啉酸)。2例≤剂量为30 mg/d的患儿恢复正常。肝活检标本中尿激酶活性显著降低随PLP的加入而显著增加,表明一个突变导致辅酶结合位点的改变。一项后续研究证实,该缺陷酶是km突变体。

Glutamic acid decarboxylase: seizures in newborns and intelligence quotient deficits 谷氨酸脱羧酶:新生儿癫痫发作与智商缺陷

Glutamic acid decarboxylase (GAD; glutamate decarboxylase), a PLP enzyme, converts glutamic acid, an excitatory amino acid, to γ-aminobutyric acid, the most important inhibitory neurotransmitter in the central nervous system (up to one-third of synapses in the brain use γ-aminobutyric acid as an inhibitory signal). Defects in GAD result in seizures in newborns (see OMIM 266100), but it is not clear whether the seizures are due to too little γ-aminobutyric acid or too much glutamic acid (65). Intravenous injection of 100–200 mg pyridoxine generally stops the seizures (66). One infant with pyridoxine-dependent seizures was shown to have decreased γ-aminobutyric acid production; the seizures stopped within 5 min of the administration of 100 mg pyridoxine. More than 50 cases of pyridoxine-dependent seizures have been reported since 1954 (67).

谷氨酸脱羧酶(GAD),一种可将转谷氨酸,一种兴奋性氨基酸,转化为GABA,中枢神经系统中最重要的抑制性神经递质,的PLP酶,(多达三分之一的突触在大脑中使用,γ-氨基丁酸作为抑制信号)。GAD对新生儿癫痫发作的影响,但尚不清楚癫痫是由于γ-氨基丁酸过少还是谷氨酸过多所致。静脉注射100-200毫克吡多辛一般能阻止癫痫发作。一名婴儿因吡啶依赖发作而被证明减少了γ-氨基丁酸的产生。100 mg吡多辛给药后5 min,癫痫发作停止。自1954年以来,已报告50多例依赖于吡多辛的癫痫。

In one study of 28 infants with seizures, 3 infants had the pyri-doxine-responsive phenotype (68). In a study of 120 infants with documented repeated and intractable seizures, only 2 infants responded to pyridoxine administration, suggesting that either only a small percentage of seizures are responsive or that there are many other causes of seizures that are not due to mutations in this vitamin B-6 enzyme (69). There appear to be other enzyme defects that can lower PLP and cause pyridoxine-dependent seizures: one patient had decreased -aminobutyric acid and increased glutamic acid in the brain, but no significant difference in GAD activity was found between the patient and control sub-jects, and PLP concentrations were markedly reduced (70).

在一项针对28名癫痫婴儿的研究中,3例婴儿表现为吡多辛酸反应型。在一项对120名有反复发作和顽固性发作的婴儿的研究中,只有2名婴儿对吡多辛有反应,这表明,要么只有一小部分癫痫发作是有反应的,要么是由于维生素B-6酶的突变而导致癫痫发作的许多其他原因。似乎还有其他一些酶缺陷可以降低PLP,并导致吡多星依赖的癫痫发作:1例脑组织中氨基丁酸和谷氨酸含量下降,但与对照组相比,GAD活性无显着性差异(P>0.05)PLP浓度明显降低

In a cell line from an infant with pyridoxine-dependent seizures, GAD activity was increased when the enzyme was incubated with high PLP. The investigators speculated that the metabolic abnormality in this disorder may be a binding abnor-mality between GAD apoenzyme and PLP (71).

在婴儿依赖吡啶依赖的癫痫发作的细胞株中,当酶被高剂量的PLP孵育时,GAD活性增加。研究人员推测,这种紊乱中的代谢异常可能是gad载脂蛋白与plp的结合异常。

A 13-y-old child who died with seizures in progress had ele-vated glutamic acid and decreased -aminobutyric acid concen-trations in the frontal and occipital cortices but not in the spinal cord; concentrations of all other amino acids, except for cystathionine, were normal. PLP was reduced in the frontal cortex, and GAD activity comparable to that of control subjects was detected when the PLP concentration was > 50 mol/L (70). Response rates from 2 reports give a cumulative pyridoxine-responsiveness of 3%, although seizures may be due to many dif-ferent defective genes (68, 69).

一名13岁儿童在发作过程中死亡,其额叶和枕叶皮质谷氨酸含量下降,而脊髓中无;所有其他氨基酸的浓度,除胱硫醚外,都是正常的。PLP在额叶皮质降低,当PLP浓度>50 mol/L时,GAD活性与对照组相当。2份报告的应答率为3%,尽管癫痫发作可能是由于许多不同的缺陷基因所致。

Intelligence quotients are decreased in pyridoxine-dependent GAD patients, suggesting that the amount of pyridoxine administered should be adjusted to optimally retain intellec-tual capacity, and not just to stop seizures. A prospective open study found that an increased dose of pyridoxine was associ-ated with an improvement in intelligence quotient. It was sug-gested that pyridoxine dependency has a wider range of clinical features than classic neonatal seizures and causes specific impairments of higher function, some of which may be reversible by vitamin B-6 therapy (72).

依赖于吡多辛的GAD患者智商降低,建议应调整吡多辛的用量,使其保持最佳的智力能力,而不仅仅是为了阻止癫痫发作。一项前瞻性的开放式研究发现,随着智商的提高,吡多星的剂量增加了。据推测,吡多辛依赖症的临床表现比典型的新生儿癫痫发作有更广泛的临床特征,并会导致更高功能的特殊损害,其中有些可能通过维生素B-6治疗是可逆的。

A treatment of asthma, theophylline, depresses PLP concentrations, and may cause seizures by decreasing -aminobutyric acid production. Pyridoxine treatment reduces theophylline-induced seizures in both mice and rabbits (73).

A linkage analysis study of 2 families argued that pyridoxine-dependent seizures are not due to a Km mutation because the base pair substitutions found in the patients’ enzymes were also found in control subjects, and different maternal alleles were passed on to 2 affected children in one family (74). However, some forms of pyridoxine-dependent seizures, which are likely a disease of multiple etiologies, are probably due to Km defects affecting PLP binding by GAD (75).

治疗哮喘,茶碱,降低PLP浓度,并可能通过减少-氨基丁酸的产生而引起癫痫发作。吡多星治疗可减轻茶碱致小鼠和家兔癫痫发作,一项对2个家系的连锁分析研究表明,吡多星依赖的癫痫发作不是由km突变引起的,因为在正常人中也发现了病人酶中的碱基对替换,并将不同的母性等位基因遗传给一个家庭中的2个受影响的儿童。然而,一些依赖于吡多辛的癫痫发作可能是多种病因的疾病,可能是由于km缺陷影响了gad与plp的结合。

γ-Cystathionase: cystathioninuria, mental retardation, and diabetes γ-胱硫脲酶:膀胱硫氨酸尿、智力低下和糖尿病

After the formation of cystathionine by CBS, another PLP enzyme in the transsulfuration pathway, -cystathionase (cystathionine -lyase), converts cystathionine into cysteine and -ketobutyrate, completing the transfer of sulfur from homocys-teine to cysteine. Enzymatic defects (see OMIM 219500) result in cystathionine accumulation in the urine and tissues. The clin-ical features can include mental retardation, convulsions, throm-bocytopenia, nephrogenic diabetes insipidus, and diabetes mellitus. High-dose pyridoxine therapy can markedly reduce concentra-tions of cystathionine in the urine and blood of deficient patients; it was suggested that vitamin B-6 responsiveness “can best be explained by a structural alteration of the apoenzyme, resulting in failure to combine normally with the coenzyme” (76). This binding theory is supported by others: “The B-6-responsive form results from the synthesis of an aberrant enzyme protein exhibit-ing altered interaction with the coenzyme, thereby resulting in an inherited increase in the requirement for vitamin B-6” (77). A high percentage of the cases can be ameliorated by supplemen-tation with pyridoxine, which is associated with a reactivation of the defective enzyme and a major decrease in urinary cysta-thionine excretion; 33 of 37 cases (89%) were found to be pyri-doxine-responsive (47). This high percentage is puzzling; one possible explanation is that more severe mutant genes cause lethality and that most of the remaining genes code for a protein with a partial activity and increased Km.

在CBS形成了胱硫醚之后,转硫途径中的另一种PLP酶,γ-胱硫脲酶(胱硫醚,-裂解酶),将胱硫氨酸转化为变成半胱氨酸和-酮丁酸盐,完成硫从同型半胱氨酸向半胱氨酸的转移。酶缺陷(大剂量吡硫氨酸治疗可明显降低缺乏症患者尿和血液中胱硫醚的浓度;有人认为维生素B-6的反应性“最好的解释是酶的结构改变,导致不能正常地与辅酶结合”。这一结合理论得到了其他人的支持:“B-6反应形式是由一种异常的酶蛋白的合成引起的,它与辅酶的相互作用发生了改变,从而导致了N对维生素B-6需求的遗传增长“很高比例的病例可以通过使用吡多辛来改善,这与缺陷酶的重新激活和尿胱甘肽的大幅度减少有关。37例中33例(89%)为吡多辛反应。这一比例之高令人费解;一种可能的解释是,更严重的突变基因导致致命性,而剩下的大多数基因编码的是一种具有部分活性和增量的蛋白质。

Alanine–glyoxylate aminotransferase: hyperoxaluria and renal failure  丙氨酸-乙醛酸转氨酶:高草酸尿和肾功能衰竭

Alanine–glyoxylate aminotransferase is a liver-specific enzyme that uses a PLP cofactor to transfer the amino group from alanine to glyoxylate, forming serine and pyruvate. A primary hyperoxaluria (see OMIM 259900) caused by a functional deficiency of the peroxisomal alanine–glyoxylate aminotransferase results in an accumulation of glyoxylate that is converted to oxalate, resulting in renal deposits of calcium oxalate and renal failure. In one study, large doses of pyridoxine reduced urinary oxalate excretion in 2 of 3 patients with primary hyperoxaluria (78). Posttreatment oxalate concentrations were between pretreatment and control concentrations, and the effect of pyridoxine was maintained for 6 mo.

丙氨酸-乙醛酸转氨酶是一种肝脏特异性酶,它使用PLP辅助因子将氨基从丙氨酸转移到乙醛酸盐,形成丝氨酸和丙酮酸。原发性高草酸尿(见OMIM 259900),由于过氧化物酶体丙氨酸-乙醛酸转氨酶功能缺乏,导致乙醛酸盐转化为草酸,导致肾积草酸钙和肾功能衰竭。在一项研究中,大剂量吡多辛,在3例原发性高草酸尿中的2例尿草酸排泄减少。处理后草酸盐浓度介于预处理浓度和对照浓度之间,吡柔嗪的作用维持6mo。

A review of hyperoxaluria indicates that pharmacologic doses of pyridoxine are of benefit and that a Km mutant may be respon-sible. Pyridoxine treatment may overcome the effects of muta-tions in the gene encoding alanine–glyoxylate aminotransferase that might interfere with cofactor binding (79). It is suggested that as many as 30% of patients with type I primary hyperoxaluria respond to pyridoxine (80). A review of pyridoxine treatment, which discussed 2 recent reports including 18 patients, stated that 50% of patients are unresponsive to pyridoxine, whereas oxaluria is normalized in 20% of patients and somewhat reduced (but not to normal concentrations) in the remaining 30% (81).
对高草酸尿的回顾表明,药物剂量的吡多辛是有益的,一个Km突变体可能是可逆的。吡多辛治疗可克服丙氨酸-乙醛酸转氨酶基因突变可能干扰辅因子结合的影响。结果表明,高达30%的Ⅰ型原发性高草酸尿患者对吡多辛有反应。一篇关于吡多辛治疗的综述讨论了最近的两份报告,其中包括18名患者,其中50%的患者对吡多辛没有反应,而20%的患者尿草酸已恢复正常。并在剩余的30%中有所降低(但不降至正常浓度)

Physicians may consider treating with alanine in addition to pyridoxine to determine the optimum cocktail for minimizing oxalate accumulation. We have not seen any reports in which plasma alanine concentrations were measured after the adminis-tration of high doses.

医生可以考虑用使用丙氨酸和维生素B6进行鸡尾酒治疗,以减少草酸的累积

Aromatic-L-amino-acid decarboxylase: developmental delay  芳香-L-氨基酸脱羧酶:精神错乱

Aromatic-L-amino acid decarboxylase (AAD; see OMIM 107930)is a homodimeric PLP-containing enzyme synthesizing 2 impor-tant neurotransmitters: dopamine and serotonin (82). After the hydroxylation of tyrosine to form dihydroxyphenylalanine, cat-alyzed by tyrosine hydroxylase, AAD decarboxylates dihydrox-yphenylalanine to form dopamine. Dopamine is sequentially broken down to dihydroxyphenylacetaldehyde by monoamine oxi-dase B [amine oxidase (flavin-containing)], to dihydroxypheny-lacetic acid by aldehyde dehydrogenase, and finally to homovanillic acid by catechol O-methyltransferase. Tryptophan 5-monooxygenase produces 5-hydroxytryptophan, which is also decarboxylated by AAD to give rise to serotonin. Serotonin is broken down to 5-hydroxyindoleacetic acid. AAD deficiency is an autosomal recessive inborn metabolic disorder characterized by combined serotonin and dopamine deficiency.

芳香-L-氨基酸脱羧酶(AAD;见OMIM 107930)是一种合成2种重要神经递质多巴胺和5-羟色胺,的高二聚体的含plp酶,酪氨酸羟化形成二羟基苯丙氨酸后,通过酪氨酸羟化酶进行分析, 芳香-L-氨基酸脱羧酶将二氢-亚苯丙氨酸脱羧基,形成多巴胺.多巴胺被单胺氧化酶B分解成二羟基苯乙醛。[胺氧化酶(含黄素)],通过醛脱氢酶将二羟基苯-1-乙酸加入到二羟基苯-1-乙酸中,最后用邻苯二酚O-甲基转移酶合成高香草酸。色氨酸5-单加氧酶产生5-羟色胺,它也被AAD脱羧而产生血清素。5-羟色胺分解为5-羟基吲哚乙酸.AAD缺乏症是一种以5-羟色胺和多巴胺缺乏为特征的常染色体隐性先天代谢紊乱。

The first reported cases of AAD deficiency were monozygotic twins with extreme hypotonia and oculogyric crises (83). AAD activity was severely reduced and concentrations of dihy-droxyphenylalanine and 5-hydroxytryptophan were elevated in cerebrospinal fluid, plasma, and urine. Pyridoxine (100 mg/d) lowered dihydroxyphenylalanine concentrations in cere-brospinal fluid, but treatment with either bromocriptine or tranylcypromine was required for clinical improvement. Another AAD-deficient patient, with similar presentation, also had greatly reduced activity of AAD in plasma (84). Similar to the first reported cases, combined treatment with pyridoxine,bromocriptine, and tranylcypromine produced some clinical improvement. Several other cases of AAD deficiency have appar-ently benefited from high-dose pyridoxine treatment (85).
首次报告的AAD缺乏症病例为同卵双生子,伴有极度低张力和眼震性危象。AAD活性严重下降,二羟基苯丙氨酸浓度降低而脑脊液、血浆、尿中5-羟色胺升高。B6(100 mg/d)可降低脑脊液中二羟基苯丙氨酸的浓度,但临床上仍需用溴隐亭或三聚氰胺治疗。另一例aad缺陷患者,具有类似的表现,也大大降低了血浆中aad的活性。与第一次报告的病例相似,联合使用吡柔嗪、溴隐亭和三聚氰丙胺可使临床有所改善。其他几例AAD缺乏症患者已从大剂量吡多星治疗中获益惊人。

Housekeeping -aminolevulinic acid synthase: sideroblastic anemia 铁粒幼细胞贫血

The mapping of a second -aminolevulinic acid synthase (5-aminolevulinate synthase) gene, ALAS1, to an autosome, chro-mosome 3, rules it out as the site of the primary defect in X-linked sideroblastic anemia. It was concluded that this gene is a house-keeping form of ALAS (see OMIM 125290) because it is expressed in all cell types including erythroid cells; thus, the gene is designated ALAS1 to distinguish it from the red cell–specific form, ALAS2 (86).

第二氨基乙酰丙酸合酶的定位基因(5-氨基酮戊酸合酶),ALAS 1,常染色体,Chro-mosome 3,排除它为X-连锁铁粒母细胞性贫血的原发缺陷部位。由此得出结论,这种基因是一种令人不快的家常便饭(见Omim125290)。因为它在包括红系细胞在内的所有细胞类型中都有表达;因此,该基因被命名为ALA1,以将其与红色细胞区分-特异性形式,ALAS2(86)。

In a study of 20 patients with sideroblastic anemia, 3 patients showed low ALAS activity that was corrected by PLP in vitro, and 2 other patients were found to be responsive to pyridoxine (20 mg/d) (87). When 1 of these 2 patients was taken off pyridoxine, ALAS activity, as measured in bone marrow, fell markedly unless PLP was added in vitro. Additionally, the Km of the enzyme for PLP was substantially greater (2.5 times) than that of a control sample. However, it is unclear whether these are ALAS1 or ALAS2 defects.

对20例铁质母细胞性贫血患者的研究,3例患者经体外PLP校正后,出现较低的AlAs活性;另外两名病人对吡多辛(20毫克/天)有反应。当这2名病人中有1名被摘除吡多辛时,AlAs活性,在骨髓中,除非在体外加入PLP,否则骨髓中PLP的含量明显下降。此外,PLP酶的Km远大于对照样品的2.5倍。但是,尚不清楚这些缺陷是ALAS 1还是ALAS 2缺陷。

A 70-y-old who exhibited an attack of polymorphic, hypochronic anemia, with increased serum iron and numerous ringed sider-oblasts in the bone marrow, was determined to have pyridoxine-responsive primary acquired sideroblastic anemia (88). Administration of pyridoxine (initially 200 mg/d, then 600 mg/d) caused a complete remission of all hematologic abnormalities. ALAS activity was increased to 50% of control with 600 mg pyridoxine/d. The activity could be further increased to 100% of control in vitro with 1000 mol/L PLP. This defect could also be in ALAS1 or ALAS2.

一个70岁的老人表现出,多态性,慢性贫血,随着血清铁含量的增加和骨髓中许多环状成纤维细胞的增加,确定具有维生素B6应答的原代培养的侧粒幼细胞贫血。服用吡多辛(最初200毫克/天,然后600毫克/天)可使所有血液异常完全缓解。用600 mg吡多辛/d,可使LAS活性提高到对照的50%。1000 mol/L PLP可使体外活性进一步提高到100%。此缺陷也可能出现在ALAS 1或ALAS 2中。

β-Alanine -ketoglutarate transaminase: Cohen syndrome β-丙氨酸酮戊二酸转氨酶:科恩综合征

β-Alanine -ketoglutarate transaminase (AKT; 4-aminobutyrate aminotransferase) is involved in the formation of malonic semi-aldehyde from -alanine. Children with AKT deficiency have Cohen syndrome (see OMIM 216550), which involves hypoto-nia, midchildhood obesity, mental deficiency, and facial, oral, ocular, and limb anomalies. A case report of a girl with features of the syndrome reported a response to 100 mg pyridoxine/d for 1 mo, with a normalization of electroencephalogram and a sub-siding of lethargy. The girl was hospitalized once when she missed a week of pyridoxine treatment, but reinstatement of the treatment resulted in more improvement. Cultured skin fibro-blasts from the girl showed a toxic response to -alanine with a 50% reduction in growth. The addition of 100 mol pyridoxine/L to the cells abolished the toxic effects and increased AKT activ-ity more than 2-fold (89).

β-丙氨酸酮戊二酸转氨酶(AKT;4-氨基丁酸氨基转移酶)与丙氨酸形成丙二醛有关。AKT缺乏症儿童Cohen综合征(见OMIM 216550),它涉及睡眠不足,儿童中期肥胖,精神缺陷,以及面部,口腔,眼睛和肢体异常.一例以该综合征为特征的女孩报告了100毫克吡多星/日的疗效,疗程为1mo,有正常的脑电图和昏睡症状。这名女孩因错过一周的吡多辛治疗而住院一次,但恢复治疗后情况有了更大改善。从女孩培养的皮肤成纤维细胞显示了对丙氨酸的毒性反应,生长下降了50%。100 mol吡多辛/L可消除细胞毒性作用,使AKT活性提高2倍以上。

Autism 孤独症
Autism (a developmental disorder that involves impaired social interactions and deviant behavior) and its associated behaviors are thought to affect 5 in 10 000 individuals [and as many as 1 in 300 in some US communities (90)]. Autism may be due to defects in a PLP-requiring enzyme or enzymes involved in the metabolism of serotonin and dopamine, although a genetic link to a vitamin B-6–requiring enzyme has not been established. The most replicated clinical sign of autism is an elevation of whole-blood serotonin (5-hydroxytryptamine), which is found in > 30% of patients (91). Increased concentrations of homovanillic acid, a breakdown product of dopamine, have also been found in several autistic patients. Pyridoxine therapy has been reported to be successful in autism, raising the possibility that a PLP-requiring enzyme might be defective in those patients responsive to vitamin B6. (PLP is a coenzyme that forms a Schiff base with an amino group in its catalytic action, so that enzymes with PLP metabolize amino acids or other amines, such as dopamine and serotonin.) The only PLP-requiring enzyme directly involved with the synthesis or degradation of dopamine and serotonin is AAD (ie, dihydroxyphenylalanine decarboxylase). The finding in some vitamin B-6–responsive patients, namely elevated homovanillic acid that is at least partially reversible with pyri-doxine therapy (92), does not suggest a defect in this enzyme. Additionally, cases of AAD deficiency have been reported in the literature (see the discussion of AAD above) and result only in a very severe inborn metabolic disorder involving deficient con-centrations of dopamine and serotonin.

孤独症(一种发育障碍,涉及受损的社会交往和异常行为)及其相关行为被认为影响到每万人中有5人。[在一些美国社区,每300人中就有1人】。孤独症可能是由于PLP所需的酶或酶的缺陷,这些酶参与了5-羟色胺和多巴胺的代谢,虽然与维生素B-6需要酶的基因联系尚未确定。孤独症最复制的临床体征是全血中5-羟色胺(5-羟色胺)的升高,在超过30%的病人中发现。在一些孤独症患者中也发现了多巴胺分解产物高香草酸浓度的增加。据报道,吡多辛治疗孤独症是成功的,增加了一种PLP所需的酶可能在那些对维生素B6有反应的病人中有缺陷的可能性。(PLP是一种辅酶,在其催化作用中形成带有氨基的Schiff碱,因此PLP酶代谢氨基酸或其他胺,如多巴胺和5-羟色胺。)唯一与多巴胺和5-羟色胺的合成或降解直接相关的PLP需要酶是AAD。(即二羟基苯丙氨酸脱羧酶)。一些维生素B-6反应灵敏的病人的发现,即升高的高香草酸,与吡多辛治疗至少部分可逆。并不表示这种酶有缺陷。此外,文献中还报道了AAD缺乏症的病例(见上文对AAD的讨论)并且仅导致非常严重的先天性代谢紊乱,涉及多巴胺和5-羟色胺的缺乏浓度。


It remains to be seen whether other enzymes in the metabolic pathways of these neurotransmitters may be responsible for the various forms of autism that involve altered neurotransmitter metabolism. Autism is diagnosed by clinical, not biochemical, indexes. Thus, if different autistic patients harbor mutations in dif-ferent metabolic enzymes, it may be possible to reverse the effects of autism by targeting a treatment to each individual patient. In addition to PLP, the coenzymes FAD, NAD, S-adenosylmethion-ine, tetrahydrobiopterin, and ascorbate are used by enzymes in serotonin and dopamine metabolism.

这些神经递质代谢途径中的其他酶是否与各种形式的孤独症有关,包括神经递质代谢的改变,还有待观察。自闭症是根据临床而不是生化指标来诊断的。因此,如果不同的自闭症患者存在不同代谢酶的突变,可以通过针对每个患者的治疗来逆转孤独症的影响。除PLP外,辅酶fad、NAD、S-腺苷甲基化酶、四氢生物蝶呤和抗坏血酸酶在5-羟色胺和多巴胺代谢中也起着重要作用。

Because so little is known about the biochemical basis of this condition, it is difficult to associate a treatment response with a particular biochemical or physiologic pathway; however, there have been many reports of successful treatment of autism with pyridoxine. In a survey involving 4000 questionnaires completed by parents of autistic children, high-dose vitamin B-6 and mag-nesium treatment (n = 318) elicited the best response; for every parent reporting behavioral worsening with the treatment, 8.5 parents reported behavioral improvement. The next best results were with the acetylcholine precursor, deanol (n = 121); 1.8 parents reported a favorable response for every 1 patient who reported worsening (93).

因为对这种情况的生化基础知之甚少,很难将治疗反应与特定的生化或生理途径联系起来;然而,有很多的报告,成功地治疗孤独症与吡多星。在一项涉及4000份问卷的调查中,自闭症儿童的父母填写了高剂量维生素B-6和镁治疗。得到的反应最好;每一位报告行为恶化的父母中,有8.5位家长报告行为有所改善。其次是乙酰胆碱前体,二甲基乙醇胺;1.8父母报告说,每1名报告恶化的病人有良好的反应

Sixteen autistic patients previously shown to respond to vitmin B6 treatment were reassessed and given vitamin B6 or a placebo in a double-blind study (94). Behavior deteriorated significantly during B6 withdrawal, and 11 of 15 children behaved better when given 300 mg vitamin B-6/d. The authors speculated that vitamin B-6 therapy may correct, or partially correct, a tryptophanrelated metabolic error because of a marked increase in serotonin efflux from platelets of autistic children and because large doses of vitamin B-6 elevate serotonin con-centrations (95).

在一项双盲研究中,对16例先前显示对维生素B6治疗有反应的孤独症患者进行了重新评估,并给予维生素B6或安慰剂。B6戒断期间行为明显恶化,15名儿童中有11名在服用300毫克维生素B-6/d时表现较好。作者推测维生素B-6疗法可以纠正或部分纠正,色氨酸相关代谢错误的原因是孤独症儿童血小板中的5-羟色胺外流明显增加,以及大剂量维生素B-6提高了5-羟色胺的浓度。

A double-blind trial involving 60 autistic children found that vitamin B-6 (30 mg pyridoxine hydrochloride · kg-1 · d-1 up to 1 g/d) and magnesium (10–15 mg · kg-1 · d-1) were more helpful than either supplement alone in ameliorating the various effects of autism. Patients receiving the combined treatment showed a significant (P < 0.02) decrease in homovanillic acid excretion (from 6.6 to 4.4 mol/mmol creatine) and significant clinical improvement (96).

一项涉及60名自闭症儿童的双盲试验发现,维生素B-6(30毫克盐酸吡多辛·kg-1·d-1至1g/d)和镁(10-15毫克·kg-1·d-1)比各自单独补充更有帮助。接受综合治疗的患者有显着性差异(P < 0.02),高香草酸排泄量减少(从6.6到4.4mol/mmol肌酸)和显著的临床改善

Tryptophan metabolism was studied in 19 children with various forms of psychosis including autism. Four children (includ-ing at least one who was autistic) who had abnormal tryptophanmetabolite ratios were treated with 30 mg pyridoxine/d, where-upon biochemical features normalized (97). It was thought that these children had kynureninase defects because the kynureninase reaction required greater than normal amounts of PLP to proceed normally (see the discussion of kynureninase above).

本文研究了19例儿童各种形式的精神病,包括孤独症的色氨酸代谢。4名患有色氨酸代谢物比率异常的儿童(其中至少包括一名自闭症儿童)每天服用30毫克吡多辛,生化指标恢复正常。这被认为是这些儿童的犬尿氨酸酶活性不足,犬尿氨酸酶反应比正常剂量需求更高的PLP。

More than a dozen other reports (with up to 190 participants) since 1965 and a review of controlled trials (98) have reported improvements in autistic patients with vitamin B-6 and often magnesium supplementation (99–102), although the conclusion that pyridoxine is an effective treatment of autism has been challenged: “interpretation of these positive findings needs to be tempered because of methodological shortcomings inherent in many of the studies” (92). A rebuttal (103) to this critique leaves the matter somewhat unresolved. Evidence supporting the hypothesis that defects in enzymes involved in neurotransmitter biosynthesis may be responsible for some forms of autism comes from a study showing that tetrahydrobiopterin, the cofactor for tyrosine and tryptophan hydroxylases, elicited behavioral improve-ments in 6 children with autism (104).

自1965年以来,另有十几份报告(包括190名参与者)和一项对照试验的回顾(98份)报告了患有维生素B-6和镁素的自闭症患者的病情有所改善。尽管关于吡多辛是自闭症有效治疗方法的结论受到了质疑:“对这些积极结果的解释需要加以缓和,因为许多研究在方法上存在缺陷”对这一批评的反驳(103)使问题有些得不到解决。支持神经递质生物合成相关酶缺陷可能导致某些形式孤独症的证据来自一项研究表明四氢生物蝶呤,酪氨酸和色氨酸羟化酶的辅助因子在6例孤独症患儿(104例)中引起行为改善。

Tardive dyskinesia 迟发性运动障碍

The long-term use of neuroleptic drugs for the attenuation of psychotic disorders such as schizophrenia can lead to tardive dyskinesia, a neurologic movement disorder characterized by rapid, repetitive, uncontrolled movements. There may be > 1 mil-lion cases of tardive dyskinesia in the United States today and there is some speculation that deranged metabolism of amino acid–derived neurotransmitters is responsible for the disease. The involvement of PLP in dopamine, serotonin, and -aminobutyric acid metabolism may be the reason for the first clinical applica-tions of pyridoxine in the treatment of tardive dyskinesia; pyri-doxine-responsiveness has been reported.

长期使用抗精神病药来减轻精神分裂症等精神疾病会导致迟发性运动障碍,一种神经运动障碍,以快速、重复、不受控制的运动为特征。今天美国可能有超过1百万的迟发性运动障碍病例,有人猜测氨基酸来源的神经递质代谢紊乱是造成这种疾病的原因之一。PLP参与多巴胺、5-羟色胺和-氨基丁酸的代谢可能是首次临床应用吡多辛治疗迟发性运动障碍的原因。据报道,免疫应答。

A double-blind, placebo-controlled crossover study found high doses of pyridoxine (≤400 mg/d) to be effective in reducing symp-toms of tardive dyskinesia in patients with schizophrenia (105). Pyridoxine or placebo was added to the normal neuroleptic treatment of all 15 patients in the study for 4 wk at a time, split by a 1-wk washout period. Pyridoxine treatment invoked improvements in both the dyskinetic movement and Parkinsonian subscales with returns to baseline with removal from pyridoxine. An earlier pilot study by the same group showed significant clinical improvement in 4 of 5 tardive dyskinesia patients given 100 mg pyridoxine/d on top of their normal treatment (106). Three of the responders also showed significant improvement on the brief psychiatric rating scale.

一项双盲安慰剂对照研究发现大剂量吡多星(≤400 mg/d)治疗精神分裂症迟发性运动障碍的疗效观察。将吡多辛或安慰剂加入到所有15名患者的正常抗精神病药物治疗中,每次4wk,分裂为1 wk冲洗期。吡多星治疗在运动障碍和帕金森氏次级量表上都有改善,从吡多辛中移除后恢复到基线水平。同一组早期的一项初步研究显示,5例迟发性运动障碍患者中有4例在正常治疗的基础上服用100 mg吡多辛/d,临床有明显改善。其中三名反应者在简短的精神病评定量表上也有明显的改善。

The relation between tardive dyskinesia susceptibility and polymorphisms in dopamine and serotonin receptor genes has been a focus of exploration. Homozygosity for the Ser9→Gly polymorphism in the dopamine D3 receptor was higher in schizophrenics with tardive dyskinesia (22%) than without (4%), suggesting that the glycine allele may be a risk factor for developing tardive dyskinesia (107). A similar study supports the involvement of Ser9→Gly in tardive dyskinesia risk, although the presence of tardive dyskinesia was higher in heterozygotes than in either homozygous group (108). The Thr102→Cys polymorphism in the serotonin type 2A receptor gene has also been investigated, although contradictory results leave the matter unresolved as to which allele may be associ-ated with schizophrenia, tardive dyskinesia, or both. A poly-morphism might code for a receptor that has a decreased neurotransmitter binding and the capacity to be stimulated by a pyridoxine-induced increase of neurotransmitter level (95), but before any such hypothesis is taken seriously more detailed biochemical evidence is necessary.

迟发性运动障碍易感性与多巴胺和5-羟色胺受体基因多态性的关系一直是研究的热点。多巴胺D3受体9→Gly多态性在迟发性运动障碍精神分裂症患者中的纯合性较高(22%)与无(4%)相比,甘氨酸等位基因可能是迟发性运动障碍的危险因素。一项类似的研究支持Ser9→Gly参与迟发性运动障碍的风险,虽然杂合子中迟发性运动障碍的存在高于纯合子组。本文还对5-羟色胺2A受体基因Thr 102→Cys多态性进行了研究。虽然有矛盾的结果,但对于哪种等位基因可能与精神分裂症、迟发性运动障碍或两者兼而有之,这一问题仍未解决。多态性可能意味着受体的神经递质结合减少,并且被吡多辛诱导的神经递质水平的增加所刺激的能力。但在认真对待任何这样的假设之前,更详细的生化证据是必要的。

Tissue concentrations and toxicity 组织浓度和毒性

Pyridoxine’s active role in ameliorating many cases of genetic disease involving enzymes that require a PLP cofactor is clear. Plasma PLP concentrations correlate well with tissue PLP concentra-tions in rats (109), and thus serve as a good indicator of vitamin B-6 status. There is a linear relation between vitamin B-6 intake and plasma concentrations of PLP (up to an intake of 3 mg/d in humans, which correlates with a plasma concentration of 60 nmol/L) (7). This proportional relation has been shown to hold even at 25 mg/d, resulting in a plasma PLP concentration of 200 nmol/L (110). A double-blind study investigating high-dose vitamin B-6 treat-ment of tardive dyskinesia showed that baseline plasma PLP (49 nmol/L) could be raised >14 times (690 nmol/L) safely with 400 mg/d pyridoxine (105). A rat study referenced in the DRI pub-lication showed that extremely large doses are well absorbed (7).

吡多星在改善许多需要PLP辅助因子的酶的遗传病中的积极作用是显而易见的。血浆PLP浓度与大鼠组织PLP浓度相关性良好。从而作为维生素B-6状态的一个很好的指标.维生素B-6摄入量与血浆PLP浓度呈线性关系。(人体摄入3mg/d,与血浆浓度60 nmol/L相关。这一比例关系被证明即使在25毫克/天时也保持不变,从而使血浆plp浓度达到200 nmol/L。对大剂量维生素B-6治疗迟发性运动障碍的双盲研究表明,400 mg/d吡啶可使基础血浆plp(49 nmol/L)安全升高14倍(690 nmol/L)。DRI公开引用的一项大鼠研究表明,极大剂量的药物被很好地吸收。

The higher concentrations of PLP likely facilitate apoenzyme-coenzyme interaction, and hence higher enzymatic activity, although it should be noted that numerical discrepancies do exist in the literature. Normal serum PLP concentrations appear to be 60 nmol/L, whereas control Km concentrations have been described in the mol/L range for some enzymes (eg, OAT and CBS).

较高浓度的PLP可能会促进酶与辅酶的相互作用,因此,更高的酶活性,虽然应该指出,数量上的差异确实存在的文献。正常血清PLP浓度似乎为60 nmol/L,而对照Km浓度则被描述为某些酶的浓度在mol/L范围内。(如OAT和CBS)。

An upper limit exists as to pyridoxine administration. Although dosages in the hundreds of milligrams have been safely applied, reports exist of neurotoxic effects with very high vitamin B-6 usage. One review advises avoiding doses >1000 mg pyridoxine/d (47). The tolerable upper intake level (UL) of pyri-doxine for normal use is 100 mg/d (7); however, the severity of some genetic diseases has reasonably prompted physicians to prescribe higher doses.

吡咯烷酮的使用存在上限,尽管数百毫克的剂量已经安全地应用了,有报道说,维生素B-6的使用率很高,有神经毒性作用。份评论建议避免剂量超过1000毫克的吡多辛/d,正常使用吡多辛的可耐受上限摄入量为100毫克/天。然而,一些遗传病的严重程度合理地促使医生开更高剂量的处方。

THIAMINE (VITAMIN B-1) 硫胺素(维生素B1)

The DRIs for thiamine for men and women are 1.2 and 1.1 mg/d,respectively (7). Thiamine is phosphorylated to form TPP, the cofactor used by many enzymes. The crystal structure of at least one of these enzymes has been solved (111) and critical residues in the TPP binding site have been identified. The thi-amine-dependent enzymes discussed in this section are sum-marized in Table 4.

男性和女性对硫胺素的DRI分别为1.2和1.1毫克/天,硫胺素被磷酸化形成TPP,TPP是许多酶所使用的辅助因子。其中至少一种酶的晶体结构已被解决。并确定了TPP结合位点中的关键残基。表4概述了本节讨论的这些胺类依赖酶.

Branched-chain -ketoacid dehydrogenase: maple syrup urine disease (ketoacidosis, mental retardation, and ataxia)

支链-酮酸脱氢酶:枫糖浆尿病(酮症酸中毒、精神发育迟缓和共济失调)

The branched-chain -ketoacid dehydrogenase (BCKAD) multienzyme mitochondrial complex is composed of 3 subunits: an E1 component (TPP-dependent decarboxylase) containing and  subunits, an E2 component (lipoate-containing acyl-transferase), and an E3 component (FAD- and NAD-containing dihydrolipoyl dehydrogenase), the latter of which is also a component of pyruvate and -ketoglutarate dehydrogenases. BCKAD is responsible for the oxidative decarboxylation of -ketoacids of the 3 branched-chain amino acids valine, leucine, and isoleucine. Genetic defects in the complex cause maple syrup urine disease (see OMIM 248600), which involves ketoacidosis, mental retardation, ataxia, and sometimes blind-ness as a result of the accumulation of -keto acids.

支链酮酸脱氢酶(BCKAD)多酶线粒体复合体由3个亚基组成:E1组(TPP依赖性脱羧酶)包含和亚基,和E2组(含脂酰基转移酶)及E3组(含FAD和NAD的二氢硫辛醇脱氢酶),后者也是丙酮酸和α-酮戊二酸脱氢酶的组成部分。BCKAD负责3种支链氨基酸-酮酸的氧化脱羧,缬氨酸、亮氨酸和异亮氨酸。复杂原因枫糖浆尿病的遗传缺陷(见OMIM 248600),这包括酮症酸中毒,智力迟钝,共济失调,有时由于-酮酸的积累而导致失明。

In 1985, thiamine responsiveness was reported in 12 patients who were fed thiamine in doses ranging from 10 to 1000 mg/d (112). The accumulation of ketoacids was shown to return to normal  after thiamine feeding (113). In one thiamine-responsive maple syrup urine disease cell line (WG-34) the Km for TPP (as meas-ured via BCKAD decarboxylation activity) was found to be 16 times higher than normal (114). The sequence of the WG-34 mutant has been determined and unexpectedly, the dihy-drolipoamide acyltransferase component of the complex was found to be altered. It is possible that the presence of a normal E2 is essential for the efficient binding of TPP to E1 (115). Other genes from thiamine-responsive patients have been sequenced and the E2 subunit was found to be altered in ≥ 2 other patients (116–118). It appears that mutations in E2 are responsible for the thiamine-responsive versions of maple syrup urine disease and it has been suggested that this E2 defect impairs the E1-E2 interaction where the TPP molecule must bind, thus increasing the cell’s requirement for thiamine and TPP (116).

一九八五年,12名服用硫胺素10至1000毫克/日的病人报告了硫胺素的反应性。经硫胺素喂养后,酮酸的积累恢复正常。在一株硫胺素敏感的枫树糖浆尿病细胞系(wg-34)中,tpp的km值(通过bCKad脱羧活性测定)比正常人高16倍。WG-34突变体的序列已经确定,而且出乎意料,该复合物的二氯硫磷酰胺酰基转移酶组分发生了改变。正常E2的存在可能对TPP与E1的有效结合至关重要。对硫胺素应答患者的其他基因进行了测序,并在≥2其他患者中发现E2亚基发生了改变。看来E2的突变是导致硫胺素应答的枫树糖浆尿病的原因之一,并且这一E2缺陷损害了E1-E2的相互作用,在这种情况下,TPP分子必须结合在一起,从而增加细胞对硫胺素和TPP的需求

The crystal structure of the TPP binding portion of the BCKAD complex has been determined as well as the effects of various maple syrup urine disease mutations on the enzyme. One mutation (E1 N222S) increased the Km for TPP in a nonrespon-sive patient. The other 3 mutations, which are described as affecting cofactor binding, all resulted in nonresponsive maple syrup urine disease. Another residue, E1 N126, which is altered in some patients with maple syrup urine disease, affects interface interaction in the complex and may be involved with subunit association and K+ binding (111). (See the discussion of potas-sium in the section on hormones, amino acids, and metals.) It remains to be seen whether some of the other mutations, specifically in the intermediate or thiamine-responsive patients, also result in an increased Km for TPP.

In 9 thiamine-dependent cases, the decarboxylation activity (which is a measurement of overall BCKAD activity) ranged from 3% to 40% of normal (119). In one case, the mutant enzyme was shown to be heat labile and stabilized by increased TPP (120). No adequate reports of the percentage of cases that are remediable by thiamine are available. Although the enzyme complex also uses NAD, FAD, and dihydrolipoic acid as cofac-tors in addition to the Mg2+ salt of TPP, it appears that the thera-peutic application of niacin, riboflavin, and lipoic acid has not been attempted. NAD, CoA, and Mg2+ were tried in cell culture but were ineffective (121).

测定了BCKAD复合物TPP结合部分的晶体结构,以及各种枫糖浆尿病突变对酶的影响。一个突变(E1,N222S)增加了非反应性患者TPP的Km。其他3种突变,这些都被描述为影响辅助因子结合,所有的结果都没有反应的枫树糖浆尿病。另一种残留,E1,N 126,在一些枫树糖浆尿病患者中有改变。,影响复杂环境中的界面交互作用,可能与亚基关联和K结合有关。(参见激素、氨基酸和金属一节中对铯的讨论。)其他一些突变,特别是中间或硫胺素反应中的突变,还有待观察。我的患者也会导致TPP的KM增加。

In one case, supplementation with oral thiamine reversed the blindness that sometimes accompanies the disease (122). Another noteworthy thiamine-responsive case involved a compound heterozygote with a large deletion and a 1002G→A transition at an exon 8 splice site that resulted in exon skipping and the tran-scription of different length mRNAs (117). The mechanism for this thiamine response remains to be explained.

在一种情况下,口服硫胺素可以逆转有时伴随疾病的失明现象。另一个值得注意的硫胺素应答病例涉及一个大缺失的复合杂合子和第8外显子剪接位点上的1002G→A转变。这导致了外显子的跳过和不同长度的mRNAs的跨写。这种硫胺素反应的机制仍有待解释。

The data suggest that combination therapy with thiamine, lipoic acid, riboflavin, nicotinamide, and adequate potassium [for which the recommended dietary allowance intake is 2000 mg/d (9)] may be optimal for the initial treatment of patients with maple syrup urine disease. Potassium might be beneficial because K+ is required for the stabilization of E1 by TPP. The stabilizing effect of K+ on BCKAD was shown in the rat liver BCKAD enzyme (123) as well as in the human E1 protein (124). Both groups observed a depen-dence of enzyme activity on the concentration of potassium salts.

数据表明硫胺素联合治疗,硫辛酸、核黄素、烟碱和足够的钾[推荐摄入量为2000 mg/d(9)]可能是治疗枫糖浆尿病的最佳方法。钾可能是有益的,因为K是稳定E1的TPP所必需的。K对大鼠肝脏BCKAD的稳定作用以及人的E1蛋白。两组均观察到酶活性对钾盐浓度的依赖关系。

Pyruvate decarboxylase: Leigh disease (lactic acidosis, ataxia, and mental retardation) 丙酮酸脱羧酶::利病(乳酸酸中毒、共济失调和智力迟钝)

Pyruvate decarboxylase is part of the pyruvate dehydrogenase multienzyme mitochondrial complex (PDHC) that uses TPP, lipoic acid, CoA, FAD, and NADH coenzymes to catalyze the conversion of pyruvate to acetyl-CoA (see OMIM 312170). The gene encoding the E1 peptide of the E1 subunit (pyruvate decar-boxylase), which binds TPP, is located on the X chromosome. Genetic defects in the complex can lead to lethal lactic acidosis, psychomotor retardation, central nervous system damage, ataxia, muscle fiber atrophy, and developmental delay (125).

丙酮酸脱羧酶是丙酮酸脱氢酶多酶线粒体复合物(PDHC)的一部分,它使用TPP,硫辛酸、辅酶A、脂肪酸和NADH辅酶催化丙酮酸合成乙酰辅酶(见OMIM 312170)。编码与TPP结合的E1亚单位(丙酮酸脱氢酶-BOXYLase)的E1肽的基因位于X染色体上。该复合体的遗传缺陷可导致致死性乳酸酸中毒、精神运动迟缓、中枢神经系统损害、共济失调、肌纤维萎缩和发育延迟(125)。

X-linked genetic defects in PDHC cause pyruvate and lac-tate accumulation and encephalomyelopathy. Twenty-six patients responded to high intakes of thiamine, ranging from 20 to 3000 mg/d. In 2 sisters (126), lipoic acid (100 mg/d) plus thiamine (3000 mg/d) were found to give the best remediation. In several cases, the mutation was shown to increase the Km of the E1 subunit for TPP and reduce the Vmax (127, 128). In several cases in which lactate was measured, thiamine lowered lactate concentrations significantly (127, 129, 130).

PDHC的X-连锁遗传缺陷可引起丙酮酸和乳酸盐的积聚和脑脊髓病.26例患者对大量摄入硫胺素(20~3000 mg/d)有反应.在2个姐妹(126)中,硫辛酸(100 mg/d)和硫胺素(3000 mg/d)的修复效果最好。在一些情况下,突变会增加tpp的e1亚基的km并降低vmax。在测定乳酸的几个病例中,硫胺素显著降低了乳酸的浓度。
In a study of 13 thiamine-responsive PDHC-deficient patients, some had a decreased affinity of PDHC for TPP that was respon-sive to TPP, whereas the PDHC activity of others increased at high TPP concentrations with no statement about enzyme affinity (131). Another group of patients with lactic acidemia and muscle fiber atrophy had TPP-responsive PDHC enzymes (1.82 and 2.63 nmol · min1 · mg protein1 with 400 mol/L TPP com-pared with 0.28 and 0.02 nmol · min1 · mg protein1, respec-tively, with 0.1 mol/L TPP) (132).

在一项针对13例硫胺素应答型PDHC缺陷患者的研究中,有些人的PDHC对TPP的亲和力降低,这是对TPP的反应,而在高TPP浓度下,其他人的PDHC活性升高,而没有关于酶亲和力的说明。另一组乳酸酸血症和肌纤维萎缩患者的pdp反应酶。

A female infant with West syndrome (a unique epileptic syn-drome with frequently poor prognosis and spasms associated with elevated blood and cerebrospinal fluid lactate concentra-tions) had thiamine-responsive PDHC deficiency (133). Lactate concentrations were lowered and symptoms disappeared when the infant was administered dichloroacetate and high doses of thiamine (500 mg/d). The patient carried the mutation Gly89→Ser in exon 3 of her PDHC E1 gene, resulting in a decreased affin-ity for TPP. PDHC activity was activated in vitro with the addition of TPP. Gly89→Ser, along with 4 other mutations in thiamine-responsive PDHC-deficient patients (His44→Arg, Arg88→Ser, Arg263→Gly, and Val389→fs) are in regions outside the TPP binding site in exon 6 (133). However, these mutations may affect overall protein conformation and indirectly decrease cofactor binding affinity. Pyridoxine was shown to be effective in several cases of West syndrome (134).

一名West综合征女婴(一种独特的癫痫综合征,预后差,痉挛与血和脑脊液乳酸浓度升高有关)硫胺素应答型PDHC缺乏症。婴儿服用二氯乙酸和大剂量硫胺素(500 mg/d)后,乳酸浓度降低,症状消失。患者携带PDHCE1基因第3外显子的Gly89基因,从而降低TPP的亲和力。在体外加入TPP后,PDHC活性被激活。Gly 89→Ser和其他4个硫胺应答型PDHC缺乏症患者(His 44→Arg、Arg 88→Ser、Arg 263→Gly和Val389→fs)在第6(133)外显子中位于TPP结合位点以外的区域。然而,这些突变可能会影响蛋白质的整体构象,间接降低辅因子结合亲和力。吡多辛对几例West综合征有效。

Three point mutations in E1-deficient patients were recreated in vitro. One mutation, Met181→Val, exhibited a 250-fold increased Km for TPP and, in addition to another studied mutation (Pro188→Leu) is involved with TPP binding. It was mentioned that an aspartate and an asparagine residue form H-bonds with and coordinate the divalent cation (Mg2+ or Ca2+). This cation interacts with the oxygen groups of the pyrophosphate portion of TPP (135). Thus, encouraging adequate intake of magnesium and calcium in PDHC-deficient patients by physicians seems reasonable. The Met181→Val mutation also raised the Km for pyruvate 3-fold (135). Physicians might consider treating PDHC-deficient patients with precursors to all of the cofactors used by the enzyme complex: thiamine, lipoic acid, pantothenate, riboflavin, and niacin.

在体外重建E1缺乏患者的三点突变。一次突变,其中一个突变,Met181TPP→Val,表明TPP的Km增加了250倍,此外,另一个被研究的突变(Pro188→Leu)也参与了TPP的结合。研究表明,天冬氨酸和天冬酰胺残基与二价阳离子(Mg2或Ca2)形成H键,并与其配位。这种阳离子与TPP的焦磷酸盐蛋白氧基团配合,因此,医生鼓励PDHC缺乏症患者摄入足够的镁和钙似乎是合理的.Met181→Val突变也使丙酮酸的Km增加了3倍。医生可能会考虑用酶复合物所使用的所有辅助性因子来治疗PDHC缺乏的患者:硫胺素、硫辛酸、泛酸、核黄素和烟酸。

Thiamine transporter, thiamine pyrophosphokinase, and -ketoglutarate dehydrogenase: thiamine-responsive megaloblastic anemia

硫胺素转运体,硫胺焦磷酸激酶和-酮戊二酸脱氢酶:硫胺反应的巨幼细胞性贫血

Thiamine-responsive megaloblastic anemia (see OMIM 249270) can be caused by defects in a putative thiamine transporter, thi-amine pyrophosphokinase (TPK), and -ketoglutarate dehydro-genase [KGDH; oxoglutarate dehydrogenase (lipoamide)]. The putative thiamine transporter, encoded by SLC19A2, is homolo-gous to reduced folate carrier proteins and may bring thiamine into cells. TPK is responsible for the phosphorylation of thiamine to TPP cofactor. KGDH is one of the thiamine-dependent dehydroge-nases that binds TPP by an E1 carboxylase (see also the discussions of BCKAD and PDHC above).

硫胺反应性巨幼细胞性贫血(见OMIM 249270)可能是由推定的硫胺素转运蛋白、Th1-胺焦磷酸激酶(TPK)和-酮戊二酸脱氢酶中的缺陷引起的,[KGDH; oxoglutarate dehydrogenase 酮戊二酸脱氢酶(2-氧(代)异戊酸脱氢酶)]。SLC19A2编码的硫胺素转运体与叶酸载体蛋白具有同源性,可将硫胺引入细胞。Tpk负责硫胺素磷酸化为TPP辅助因子。KGDH是由E1羟甲基纤维素结合TPP的硫胺素依赖性脱氢基酶之一。(另见上文BCKAD和PDHC的讨论)。
Mutations in SLC19A2 (136, 137) and defects in TPK (138, 139) and KGDH (140, 141) have all been found in patients with thiamine-responsive megaloblastic anemia. Thiamine-responsive megaloblastic anemia, first described by Rogers et al (142) in 1969, is an autosomal recessive condition with an early onset and is characterized by the triad of megaloblastic anemia, dia-betes mellitus, and sensorineural deafness.

SLC19A2中的突变和TPK及KGDH中的缺陷,均在硫胺素应答型巨幼细胞性贫血患者中发现。硫胺素反应性巨幼红细胞贫血,DescribedbyRogers等人首次于1969年提出,这是一种常染色体隐性疾病,发病早,主要表现为巨幼细胞性贫血、糖尿病和感音神经性耳聋。

Mutations in the gene for the putative thiamine transporter, SLC19A2 (see OMIM 603941), were found in all affected individuals in 6 families with thiamine-responsive megaloblastic anemia (136). Another study found similar results and supports the putative role of SLC19A2 in some forms of thiamine-responsive megaloblastic anemia (137). There is evidence that there is a low-affinity thiamine transporter and that this transporter is responsi-ble for the clinical thiamine-responsiveness, partially correcting for the decreased intracellular thiamine concentrations that result from the defective high-affinity transporter, SLC19A2 (143). The low-affinity version may be the recently identified thiamine transporter SLC19A3 (144). Such a bypass would not involve overcoming a Km defect. Both thiamine transport and TPK were thought to be the enzymes affected in a group of 7 patients with thiamine-responsive megaloblastic anemia (143).

被认为是硫胺转运体的基因突变,SLC19A2(见OMIM 603941),在6个硫胺素应答性巨幼细胞性贫血家系的所有患者中均有发现。另一项研究发现了类似的结果,并支持SLC19A2在某些形式的硫胺素反应的巨幼细胞性贫血中的作用。有证据表明存在一种低亲和力的硫胺素转运体,并且这种转运体对临床硫胺素的反应性是有效的,部分校正了减少的内标物(Intracel)。由缺陷的高亲和力转运体SLC19A2引起的环状硫胺浓度。低亲和力版本可能是最近发现的硫胺转运体SLC19A3。这样的绕行将不涉及克服KM缺陷。7例硫胺素反应性巨幼细胞性贫血患者中,硫胺素转运和tpk均被认为是受影响的酶。

TPK activity was reduced in a patient with thiamine-responsive megaloblastic anemia in whom 60 d of thiamine therapy (50 mg/d) normalized concentrations of free and phosphorylated thiamine (139). Thiamine responsiveness was found in 2 similar cases of thiamine-responsive megaloblastic anemia with defi-cient TPK activity (138). After thiamine ingestion (75 mg/d), which raised erythrocyte TPP concentrations 1.5- and 2-fold in the patients, hematologic findings returned to normal and insulin requirements decreased by 66%. (See OMIM 606370.)

硫胺素应答性巨幼细胞性贫血患者Tpk活性下降,其中硫氨治疗60d(50 mg/d),游离和磷酸化硫胺素(139)正常浓度。在2例tpk活性低下的硫胺素应答型巨幼细胞性贫血患者中发现了硫胺素反应性。硫胺素摄入(75mg/d)后,患者红细胞TPP浓度升高1.5倍和2倍,血液学发现恢复正常,胰岛素需求下降66%(见OMIM 606370。)

Deficient KGDH activity (see OMIM 203740) in one patient with thiamine-responsive megaloblastic anemia was stimulated by TPP titration. Near normal activity was reached with 0.75 mol TPP/L, whereas control subjects were not responsive (140). The KGDH activity in another patient was 2% of that of a control sub-ject, and a defect in binding of TPP to the KGDH complex was suggested (141). Because the KGDH complex uses other coen-zymes including lipoic acid, CoA, FAD, and NAD, patients may benefit initially from a high-dose mixture of thiamine, lipoic acid, pantothenate, riboflavin, and niacin, but controlled clinical inves-tigations are needed to validate or reject this hypothesis.

缺乏KGDH活性(见OMIM 203740)在1例患者中,通过TPP滴定刺激了硫胺素响应的巨幼细胞贫血。0.75mol TPP/L,活性接近正常。而对照组则没有反应。另一例患者的kgdh活性为对照组的2%,提示tpp与kgdh复合物的结合存在缺陷。由于kgDH复合物使用其他coen-酶,包括硫辛酸、coA、fad和nod,患者最初可能受益于高剂量的硫胺素混合物,硫辛酸,泛酸,核黄素和烟酸,但控制的临床入侵,需要验证或拒绝这一假设。

Oxidation of -ketoglutarate, pyruvate + malate, and malate + palmitate: lactic acidosis and cardiomyopathy
氧化-酮戊二酸,丙酮酸-苹果酸,和苹果酸棕榈酸盐:乳酸酸中毒和心肌病

Cardiomyopathy and lactic acid accumulation in a neonate was remedied by feeding thiamine (50 mg/d), carnitine (2 g/d), and riboflavin (50 mg/d), which reversed the high blood lac-tate concentrations and other symptoms. The patient showed a deficiency in the oxidation of all substrates tested: pyruvate, -ketoglutarate, and palmitate. After freezing and thawing and addition of essential cofactors (TPP, CoA-SH, NAD), the activi-ties of the ketoacid dehydrogenases became normal. The appar-ent deficiency may have been caused by a primary deficiency in one of the cofactors or by a defect at the level of thiamine. Although the precise metabolic defect was not assessed, it was concluded that the patient was responsive to thiamine (145). A similar case (146) was also reversed by thiamine (50 mg/d).

用硫胺(50 mg/d)、肉碱(2g/d)和核黄素(50 mg/d)治疗新生儿心肌病和乳酸积累。从而逆转了血乳酸含量过高等症状。病人显示所有被测底物的氧化缺乏:丙酮酸,戊二酸酮,棕榈酸酯。冻融后添加必需的辅助因子(TPP、CoA-SH、NAD),酮酸脱氢酶活性正常。可怕的缺乏症可能是由一个辅助性因素中的一个初级缺乏症引起的,或者是由于硫胺素水平的缺陷造成的。虽然没有对确切的代谢缺陷进行评估,但结论是病人对硫胺素(145)有反应。类似的病例(146)也被硫胺素(50 mg/d)逆转。

Tissue concentrations and toxicity 组织浓度和毒性

The effectiveness of thiamine administration in these diseases involving several mutant genes seems clear. It has been shown that a 10-mg dose of thiamine raised serum thiamine concentrations to 24 nmol/L; concentrations returned to baseline (17 nmol/L) 6 h later (147). With higher pharmacologic doses, namely, repetitive 250-mg amounts taken orally and 500 mg/d given intramuscularly, nearly 1 wk was required for steady state plasma concentrations to be reached (148). It seems apparent that thiamine administration raises both TPP and thiamine concentrations in serum, but we have not found documentation of this.

硫胺素给药在涉及几个突变基因的这些疾病中的有效性似乎是清楚的。已经显示,10mg剂量的硫胺素升高血清硫胺素浓度为24nmol/L;浓度在6小时后恢复到基线(17 nmol/L)。随着较高的药量,即重复的250毫克口服和500毫克/天肌肉注射,需要近1周才能达到稳态血浆浓度。很明显,硫胺素的使用会提高血清中的TPP和硫胺素的浓度,但我们还没有发现这方面的文献。

There is no defined UL for thiamine because of its relative safety. Adverse effects of thiamine have been documented, although they appear to be rare. For example, in a study of 989 patients, 100 mg thiamine hydrochloride/d given intra-venously resulted in a burning effect at the injection site in 11 patients and pruritus in 1 (149).

由于硫胺素的相对安全性,它没有被定义为UL。硫胺素的副作用已被记录在案,尽管它们似乎很少见。例如,在一项对989例患者的研究中,静脉注射100毫克盐酸硫胺,11例在注射部位产生灼烧作用,1例出现瘙痒。

RIBOFLAVIN (VITAMIN B-2) 核黄素(维生素B2)

The DRI for riboflavin is 1.3 mg/d for men and 1.1 mg/d for women (7). Riboflavin kinase synthesizes flavin mononu-cleotide (FMN) from ATP and riboflavin. Flavin adenine dinucleotide (FAD) is synthesized by the subsequent adenylation of FMN by FAD synthetase. A flavin-containing cofactor, FAD or FMN, is utilized by 151 (4%) of the 3870 enzymes catalogued in the ENZYME database (6). In addition to the identification of protein motifs (eg, Rossmann folds) involved with nonadenine binding of adenylate-containing cofactors (including FAD and NAD), a common adenine moiety binding motif was recently found in a large group of FAD binding proteins (150). The pyrophosphate moiety may be most important for FAD recognition because of a strongly conserved pyrophosphate binding motif found in FAD binding protein families (151). The following enzymes requiring flavin coenzymes are summarized in Table 5.

对于男性而言,核黄素的DRI为1.3mg/d,女性为1.1mg/d。 核黄素激酶合成黄素核苷酸 (FMN) 自ATP和核黄素,核黄素腺嘌呤二核苷酸FAD是由fmn的后续腺苷化反应合成的通过FAD合成酶,一种含Flavin的辅助性因子,FAD或FMN,在酶数据库中编目的3870种酶中,有151种(4%)被利用。除了蛋白质基序的鉴定之外,(如Rossmann折叠),与非腺嘌呤结合的含腺苷酸辅因子(包括FAD和NAD),最近在一大群FAD结合蛋白中发现了一个常见的腺嘌呤结合基序。由于fad结合蛋白家族中存在一个高度保守的焦磷酸结合基序,焦磷酸基元可能是fad识别中最重要的。表5概述了下列需要Flavin辅酶的酶。

Methylenetetrahydrofolate reductase (NADPH): homocysteinemia, cardiovascular disease, migraine,neural tube defects, Down syndrome, diabetic nephropathy, congenital cardiac malformations, dementia, and male infertility

亚甲基四氢叶酸还原酶(NADPH):同型半胱氨酸血症、心血管疾病、偏头痛、神经管缺陷、唐氏综合征、糖尿病肾病、先天性心脏畸形、痴呆和男性不育

Human MTHFR (also discussed in the section on folic acid) uses both NADP and FAD cofactors to catalyze the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate (see OMIM 236250). The latter is the predominant circulatory form of folate and the main carbon donor for the remethylation of homocysteine to methionine. The 677C→T (Ala222→Val) polymorphism (TT genotype occurring in 10–20% of the population) in the human MTHFR gene results in a thermolabile enzyme with reduced activity (152). Individuals with the polymorphism have a larger pool of 5,10-methylenetetrahydrofolate and are at a lower risk of developing chromosome breaks and cancer (153) and sperm dysfunction (154) when folic acid intake is marginal. The variant enzyme, however, results in a smaller pool of 5-methyltetrahydrofolate and an accumulation of homocys-teine (155), which has been associated with an elevated risk of cardiovascular disease (51, 52). A higher frequency of the 677C→T polymorphism has been associated with cardiovascular dis-ease (156), neural tube defects (NTDs) (157), Down syndrome (158), migraine (159), diabetic nephropathy (160), congenital cardiac malformations (161), dementia (162), male infertility (163), and other conditions.

人MTHFR(在叶酸一节中也有讨论)使用NADP和FAD辅助因子催化5,10-亚甲基四氢叶酸转化为5-亚甲基四氢叶酸。(见OMIM 236250)。后者是叶酸的主要循环形式,是同型半胱氨酸再甲基化为蛋氨酸的主要碳供体。677c→T(Ala222→Val)多态性(TT基因型出现在10-20%的人群中)在人MTHFR基因中,产生一种活性降低的热摩尔酶。当叶酸摄入量是边际时。,多态个体有较大的5,10-亚甲基四氢叶酸库而且发生染色体断裂、癌症、精子功,能障碍的风险较低。然而,这种变异酶会导致较小的5-甲基四氢叶酸库和同型半胱氨酸的积累。这与心血管疾病的风险增加有关,较高频率的677 c→T多态性与心血管疾病、神经管缺陷、唐氏综合征、偏头痛、糖尿病肾病、先天性心脏畸形、痴呆、男性不孕及其他疾病易感有关。

Although individuals with the polymorphism and many of the associated conditions have typically been treated with folic acid, the precursor to the MTHFR substrate, riboflavin, the FAD precursor vitamin, may prove to be of additional benefit because the primary defect in the 677C→T mutated enzyme is altered FAD binding. The human 677C→T mutation (164) and its Escherichia coli homologue (165) were found to alter the struc-ture of MTHFR and lower the binding affinity for the FAD cofactor, while not affecting the Km for folate. It was also found that the addition of FAD to crude extracts of human lymphocytes and of recombinant human MTHFR expressed in E. coli protects both wild-type and mutant enzymes, and that the protection is more dramatic with the mutant enzyme (165). The reduced ability to bind FAD was abolished under very high concentrations (mol/L) of folate (normal serum range is nmol/L), and this mechanism was offered as the basis for the effectiveness of folic acid therapy in lowering homocysteine in those with the poly-morphism. This suggests that feeding high doses of riboflavin to raise the concentrations of FAD might be of additional benefit to folic acid in lowering homocysteine concentrations in persons homozygous for the 677C→T mutation.

虽然具有这种多态性的个体和许多相关的疾病通常都是用叶酸治疗的,MTHFR底物的前驱物,核黄素,FAD前体维生素可能会带来额外的好处因为677C或T突变的酶中的主要缺陷是改变的FAD结合。人677c→T突变及其大肠杆菌同源物可改变MTHFR的结构,降低与FAD辅助因子的结合亲和力,同时不影响叶酸的KM值。在人淋巴细胞粗提物中加入FAD和在大肠杆菌中表达的重组人MTHFR对野生型和突变型酶均有保护作用而且突变酶的保护作用更大。当叶酸浓度极高(mol/L)(正常血清范围为nmol/L)时,与FAD结合的能力减弱。为叶酸治疗降低多形性同型半胱氨酸的疗效提供了依据。这表明用高剂量的核黄素来提高fad的浓度可能对叶酸降低同型半胱氨酸的浓度有额外的好处在677c→T突变纯合子的人。

The maintenance of adequate riboflavin status is likely important for homocysteine and methylation metabolism, as suggested by the results of a rat study that showed MTHFR to be sensitive to both severe and moderate riboflavin deficiency (166). The 677C→T variant may be even more sensitive. Additionally, plasma riboflavin was found to be inversely related to plasma total homocysteine in a recent study in Norway of 423 healthy blood donors with adequate B-vitamin intake (167). Plasma total homocysteine, serum folate, serum cobalamin, serum creatinine, and MTHFR 677C→T genotype were measured, as well as both FMN and FAD. Riboflavin was found to be an independent determinant of total homocysteine status: total homocysteine was 1.4 mol/L higher in the lowest than in the highest riboflavin quartile (P = 0.008). The riboflavin–total homocysteine relation was modified by genotype (P = 0.004) and was essentially confined to subjects with the 677C→T polymorphism in the MTHFR gene. Those with the CC genotype did not show the correlation, whereas those heterozygous and homozygous for this common polymorphism (in this study, 9% were TT and 43% were CT) did show a riboflavin determinacy of homocysteine status. It was suggested that subjects with the T allele may require higher concentrations of FAD for maximal catalytic activity. The altered interaction between FAD and MTHFR sug-gests that high-dose riboflavin treatment should be studied in TT individuals, even those who have normal vitamin intakes, who might benefit by lowered homocysteine concentrations in the blood via the stimulation of MTHFR and thus a lowered risk of cardiovascular and other diseases. Another study showed an inverse correlation between the intake of several B vitamins, including riboflavin, and plasma homocysteine in atherosclerotic patients and control subjects (168). MTHFR genotype was not considered in this study.

维持足够的核黄素状态可能对同型半胱氨酸和甲基化代谢很重要,正如一项表明MTHFR对严重和中度核黄素缺乏都敏感的大鼠研究结果所表明的那样。677c→T变异体可能更敏感。此外,在挪威对423名健康献血者进行的一项研究发现,血浆核黄素与血浆总同型半胱氨酸呈负相关。测定血浆总同型半胱氨酸、血清叶酸、血清钴胺、血清肌酐、MTHFR677c→T基因型,并进行fmn和fad检测。核黄素是决定总同型半胱氨酸状态的独立决定因素:总同型半胱氨酸最低比最高的核黄素四分位高1.4mol/L(P=0.008)。核黄素-总同型半胱氨酸关系受基因型的影响(P=0.004),主要局限于基因677 c→T多态性的人群。CC基因型的人没有表现出相关性,而那些杂合子和纯合子导致了这种常见的多态性(在本研究中,9%为TT,43%为CT)表现出核黄素测定同型半胱氨酸的状态相关性。提示T等位基因的受试者可能需要较高浓度的FAD以达到最大的催化活性。FAD与MTHFR相互作用的变化表明应在TT个体中研究大剂量核黄素治疗,即使是那些维生素摄入正常的人,他们也可能受益于通过MTHFR刺激血液中同型半胱氨酸浓度的降低,从而降低患心血管疾病和其他疾病的风险。另一项研究显示,几种维生素B的摄入量成反比关系,包括核黄素,血浆同型半胱氨酸在动脉粥样硬化患者和对照组(168)。本研究未考虑MTHFR基因型。

A positive correlation was found between the 677C→T polymorphism and migraine (159), which was shown to be responsive to high-dose riboflavin treatment (400 mg/d), with a significant reduction in attack frequency (169). Those homozygous for the T allele were at a considerably greater risk of migraine than were control subjects, suggesting that homocysteine, an excitatory amino acid, is a risk factor for migraine. Seventy-four patients with migraine were compared with 261 healthy control subjects. The frequency of the TT genotype among the control subjects (9.6%) was significantly lower than in the migraine patients with aura (9/22, or 40.9%; P < 0.0001). No significant difference was found between the control subjects and the patients with migraine without aura or with tension-type headaches (159). In a randomized controlled study of 55 patients, more patients taking 400 mg riboflavin/d improved by ≥50% than did those taking a placebo: 59% of the riboflavin group responded to treatment with fewer migraine days compared with 15% for the placebo group (P = 0.002), 56% of patients in the riboflavin group responded to treatment with a decrease in attack frequency compared with 19% for the placebo group (P = 0.01), and 41% of the riboflavin patients improved on the migraine index compared with 8% for the placebo group (P = 0.01) (169). The patients with aura made up 22% of the group but were not differentiated in the analysis. This confirmed a previous open study.

677c→T多态性与偏头痛发现正相关,它对大剂量核黄素治疗(400毫克/天)是有效的,在攻击频率显著降低的情况下,那些T等位基因纯合子的人患偏头痛的风险比对照组大得多,提示同型半胱氨酸是一种兴奋性氨基酸,是偏头痛的危险因素。将74例偏头痛患者与261例健康对照者进行比较.对照组TT基因型频率(9.6%)明显低于先兆偏头痛患者(9/22,40.9%,P<0.0001)。对照组与无先兆偏头痛或紧张型头痛患者比较无显着性差异(P>0.05)。在一项对55名患者的随机对照研究中,服用400毫克核黄素/天的患者比服用安慰剂的患者多出50%的≥:59%的核黄素组治疗后偏头痛天数比安慰剂组少15%(P=0.002),56%的核黄素组对治疗有反应。与安慰剂组相比,发作频率降低19%(p=0.01),41%的核黄素患者偏头痛指数较安慰剂组提高8%(P=0.01)(169)。有先兆的患者占组的22%,但在分析中未作鉴别。这证实了先前的一项公开研究。

Riboflavin and -blockers were similarly tested for the pre-vention of headaches (170). Intensity dependence of auditory evoked cortical potentials, a measurement of cortical informa-tion processing, was found to be decreased after treatment with -blockers. Riboflavin had a clinical efficacy similar to that of -blockers in the patients, but it did not change cortical infor-mation processing. Headache frequency decreased significantly in both patient groups (P < 0.05). Eight of 15 patients responded to riboflavin (meaning a reduction in attack frequency by > 50%). It would be of interest to compare MTHFR genotype with riboflavin responsiveness in these migraine patients, although such a study has not been done (J Schoenen, personal communication, 2001).

核黄素和阻滞剂也同样用于预防头痛,听觉诱发皮层电位的强度依赖性是大脑皮层信息处理的一种测量,经-阻滞剂治疗后,听觉诱发皮层电位的强度依赖性降低。核黄素的临床疗效与受体阻滞剂相似,但不改变皮质信息处理。两组患者头痛发生率均明显降低(P<0.05)。15例患者中有8例对核黄素有反应(这意味着攻击频率减少了50%以上)。在这些偏头痛患者中比较MTHFR基因型和核黄素反应是有意义的,尽管还没有做过这样的研究 (J Schoenen, personal communication, 2001).

NTDs, which are among the most common genetic malformations, have traditionally been prevented with periconceptional folic acid supplementation. It is estimated that the fraction of NTDs due to the TT genotype in Ireland is 11.4% (157). Homocysteinemia has been implicated in NTDs, and although some studies (171) found no correlation between 677C→T and NTDs, another study (157) of 271 NTD cases and 242 controls, found a higher prevalence of the TT genotype in the cases (18.8%) than in the controls (8.3%; P = 0.0005). These findings suggest that raising MTHFR activity through riboflavin administration may complement the action of periconceptional folic acid, especially because most women carrying affected embryos have plasma and red blood cell folate concentrations well above the clinically deficient range (172). Supporting evidence for this hypothesis may come from 2 Hungarian studies that showed a multivitamin (containing 800 g folate) was more efficient than was folate alone (6 mg) in preventing the first occurrence of an NTD (173).

NTDs是最常见的遗传畸形之一,传统上是通过补充叶酸来预防的。据估计,爱尔兰TT基因型所致NTDs的比例为11.4%。同型半胱氨酸血症与NTDs有关,尽管有一些研究发现677 c→T与NTDs无相关性,另一项研究在271例NTD病例和242例对照中,发现TT基因型在病例中的患病率(18.8%)高于对照组(8.3%;p=0.0005)。这些发现提示,通过核黄素的应用来提高MTHFR的活性可能是对叶酸的补充作用,特别是因为大多数携带受感染胚胎的妇女血浆和红细胞叶酸的浓度远远高于临床缺乏的范围。支持这一假说的证据可能来自匈牙利的两项研究这表明复合维生素(含800克叶酸)比叶酸单独(6毫克)预防首次发生NTD更有效。

A positive relation between elevated homocysteine and cardiovascular disease risk has been clearly established. However, most of the > 20 studies looking at the relation of the 677C→T polymorphism to cardiovascular disease risk failed to find a positive correlation. This failure has been attributed to a lack of statistical power to detect the added risk due to the mild homo-cysteine elevation associated with the TT genotype (174). A positive correlation of cardiovascular disease with the TT geno-type was found in patients with end-stage renal disease (175),familial hypercholesterolemia (176), and cardiovascular disease alone (156, 177, 178).

同型半胱氨酸升高与心血管疾病风险之间有着明确的正相关关系。然而,在研究677c→T多态性与心血管疾病风险的关系的>20项研究中,大部分未能找到正相关关系。这一失败是由于缺乏统计能力来检测与tt基因型相关的轻度同型半胱氨酸升高而增加的风险。终末期肾病患者心血管疾病与TT基因型呈正相关。家族性高胆固醇血症,心血管疾病。

Two studies, involving 57 and 157 cases, respectively, showed the 677C→T mutation to be more prevalent among mothers of children with Down Syndrome than among control mothers (with odds ratios of 2.6 and 1.9, respectively) (158, 179). Trisomy 21 is due to maternal nondisjunction 93% of the time, and it is possible that the maternal polymorphism leads to altered folate metabolism, DNA hypomethylation, and abnormal chro-mosomal segregation. In fact, a positive correlation between the 677C→T genotype and DNA hypomethylation was been found in leukocytes of individuals with the polymorphism (180). DNA methylation was directly and significantly related to red blood cell folate concentrations in persons with the TT genotype, but not in those with wild-type MTHFR.

两项研究,涉及57起和157个案例,结果显示,677c→T突变在唐氏综合征患儿母亲中比对照组更普遍(OR值分别为2.6和1.9)。三体性21是由于母体不分离93%的时间,而母体多态性可能导致叶酸代谢改变,DNA低甲基化,以及不正常的染色体分离。事实上,在个体白细胞中发现677c→T基因型与dna低甲基化呈正相关。TT基因型者DNA甲基化与红细胞叶酸浓度直接显著相关,而野生型MTHFR者与DNA甲基化无关。

The 677C→T polymorphism and concomitant hyperhomocys-teinemia are also associated with diabetic nephropathy in patients with serum folate concentrations <15.4 nmol/L (P = 0.02) (160). Congenital cardiac malformations may be connected with the 677C→T polymorphism as well: 26 pregnancies compli-cated by fetal cardiac defects had higher amniotic homocys-teine concentrations and a higher incidence of the 677C→T polymorphism than found in 116 normal pregnancies (161). TT homozygosity is more common in infants with congenital heart disease than in control infants (181). Additionally, a higher incidence of TT was found in patients with dementia (25%) than in control subjects (12%) (162). When only study participants with hyperhomocysteinemia (concentrations ≥15 mol/L) were considered, the percentage of TT in the dementia group rose to 43% (compared with 14% in the control group), suggesting that 677C→T and homocysteine are risk factors for dementia.

血清叶酸浓度<15.4nmol/L的糖尿病肾病患者血清中677c→T多态性及伴随高同型半胱氨酸血症也与糖尿病肾病有关(P=0.02)(160)。先天性心脏畸形也可能与677c→T多态性有关:26例合并胎儿心脏缺损的孕妇羊水浓度较高,羊水浓度较高。她的677c→T多态性的发生率高于116例正常妊娠(161例)。TT纯合子在先天性心脏病患儿中比对照组更常见。此外,痴呆患者TT发生率(25%)高于对照组(12%)。仅研究高同型半胱氨酸血症(浓度为15mol/L)的受试者时,痴呆组的TT百分比上升至43%(对照组的14%),SUG677C/T和同型半胱氨酸是痴呆的危险因素。

Other mutations in MTHFR also seem to affect FAD binding and may be remedied with high-dose riboflavin treatment. The E. coli homologue of the human mutation, Arg157→Gln, displays defective flavin binding (165). Two other mutations in MTHFR, 985C→T and 1015C→T, identified in 2 patients may also decrease the binding of the FAD cofactor (182). Rosenblatt and Erbe previously studied these 2 patients and found that reductase activity was much less stable at elevated temperatures in the absence of added FAD than with the addition of 72 mol FAD/L (183). They concluded that, “There is a mutationally induced structural defect in the aporeductase as the basis for the observed alteration in thermostability, presumably reflecting reduced ability to bind the FAD cofactor” (183).

MTHFR的其他突变似乎也会影响FAD结合,并可通过大剂量核黄素治疗加以补救。人突变Arg 157→Gln的大肠杆菌同源性显示Flavin结合有缺陷。Rosenblatt和Erbe先前对这2例患者进行了研究,发现在没有添加FAD的情况下,还原酶活性在升高的温度下 比在而添加72 mol FAD/L的环境下更不稳定。他们的结论是,作为观察到的热稳定性变化的基础,脱还原酶存在突变性结构缺陷,可能反映了结合fad辅助因子的能力降低

The TT genotype has been associated with increased homo-cysteine concentrations (especially in persons with low plasma folate) (184, 185). Clinical trials of the interventions of folate, vitamins B-6 and B-12, and high-dose riboflavin treatment would be of interest in patients with the 677C→T polymorphism or any of the accompanying conditions including migraine and diabetic nephropathy.

TT基因型与同型半胱氨酸浓度升高有关(尤其是在血浆叶酸水平较低的人群中,)叶酸、维生素B-6和B-12的干预措施以及大剂量核黄素治疗的临床试验将对677 c→T多态性患者或任何伴随的cond患者感兴趣。偏头痛和糖尿病肾病。

NAD(P):quinone oxidoreductase 1: urothelial tumor risk, leukemia risk, benzene-induced hematoxicity risk
NAD(P):醌氧化还原酶1 :尿路上皮肿瘤的风险,白血病风险,苯诱导造血风险

NAD(P):quinone oxidoreductase 1 [NQO1; NAD(P)H dehy-drogenase (quinone)] utilizes NAD and FAD cofactors to catalyze the 2-electron reduction of quinones and quinonoid compounds to hydroquinones (see OMIM 125860). Normal NQO1 activity is involved in both detoxification and chemoprotection as well as in the bioactivation of some compounds, including cytotoxic antitumor agents. A polymorphic mutation in NQO1, 609C→T(TT frequency: 4–20%), which results in a Pro187→Ser amino acid substitution, has been associated with an increased risk of urothelial tumors, therapy-related acute myeloid leukemia, cuta-neous basal cell carcinomas, pediatric leukemias, and the devel-opment of benzene-induced hematoxicity in exposed workers (186).

NAD(P):醌氧化还原酶1[NQO1; NAD(P)H 脱氧核糖核酸酶(醌)】利用NAD和FAD辅助因子催化醌类和醌类化合物的2-电子还原制氢醌(see OMIM 125860). 正常的NQO 1活性参与解毒和化学保护以及某些化合物的生物活性,包括细胞毒性抗肿瘤药物。NQO 1,609 C→T的多态性突变(TT频率:4~20%),其导致PRO187或Ser氨基酸取代,会增加患尿路上皮肿瘤的风险,治疗相关的急性髓系白血病,基底细胞癌,儿童白血病,和苯对接触工人血液毒性的影响。

The data concerning an association between lung cancer risk and NQO1 genotype are contradictory. Some studies found the wild-type allele (C609) to be overrepresented in lung cancer cases relative to control subjects (187, 188), suggesting a chemo-protective role of the polymorphism (T609). In contrast, other studies found either the opposite to be true (189, 190) or that no correlation exists (191). The latter study was the largest of the NQO1 genotype and lung cancer risk studies to date, comprising 814 lung cancer patients and 1123 control subjects.

关于肺癌风险与NQO1基因型之间的关联的数据是矛盾的。一些研究发现,与对照组相比,肺癌病例中野生型等位基因(C 609)的表达过高。提示多态具有化学保护作用。相反,其他的研究发现两者都是相反的或者说不存在相关性。后一项研究是迄今为止最大的NQO 1基因型和肺癌风险研究,包括814名肺癌患者和1123名对照者。

The polymorphism results in reduced amounts of the NQO1 protein, possibly as the result of to an accelerated degradation via the ubiquitin pathway. The mutant expressed in E. coli has between 2% and 4% of the activity of the wild-type enzyme (186). The cause of both of these observations is likely to be an aber-rant binding of FAD by the mutant enzyme. The Pro187→Ser mutation disturbs the structure of the central parallel -sheet (192), resulting in a reduction in binding affinity for the FAD cofactor (193). Others found that NQO1 activity can be measured only in the presence of increased concentrations of FAD, confirming that the impairment of activity in the Pro187→Ser enzyme is due to lowered FAD affinity (Ivonne Rietjens, unpub-lished observations, 2001).
这种多态性导致NQO 1蛋白的数量减少,可能是通过泛素途径加速降解的结果。在大肠杆菌中表达的突变体具有2%~4%的野生型酶活性。这两种观察的原因很可能是突变酶对FAD的快速结合。Pro187→Ser突变干扰了中心并行片的结构。导致与FAD辅助因子结合的亲和力降低,另一些人认为,只有在FAD浓度增加的情况下才能测量NQO 1的活性,证实Pro187→Ser酶活性受损是由于FAD亲和力降低所致(Ivonne Rietjens, unpub-lished observations, 2001).

These data suggest that individuals with the NQO1 polymor-phism might benefit from high-dose riboflavin treatment by reductions in cancer risk. Further studies should be done to verify or reject this theory.

这些数据表明,具有NQO 1多聚物的个体可能通过降低癌症风险而受益于大剂量核黄素治疗。应该做进一步的研究来验证或否定这一理论。

Protoporphyrinogen oxidase: variegate porphyria and motor neuropathy
原卟啉原氧化酶:混合型卟啉病和运动神经病变

Protoporphyrinogen oxidase, a mitochondrial flavoprotein, catalyzes the oxygen-dependent oxidation of protoporphyrinogen IX to protoporphyrin IX, the penultimate step in the heme biosynthetic pathway. Protoporphyrinogen oxidase deficiency results in variegate porphyria (see OMIM 176200), which involves various neuropsychiatric symptoms, including bulbar paralysis, quadriplegia, and motor neuropathy. Protoporphyrinogen oxidase shares significant homologies with several oxidases (eg, monoamine oxidases) that contain an FAD binding motif at the amino terminus (194). The Arg59→Trp mutation, one of fewer than a dozen mutations reported in the gene encoding pro-toporphyrinogen oxidase to date and common in South Africa [because of to a 17th century Dutch immigrant founder effect (195)], affects the FAD binding motif and is suspected to alter the FAD binding affinity of protoporphyrinogen oxidase. A sim-ilarity is postulated to X-linked sideroblastic anemia, which has been successfully treated with pyridoxine (see the discussion of ALAS2 in the section on pyridoxine). A similar approach with riboflavin supplementation may be useful in the treatment of persons with variegate porphyria whose mutations affect the FAD binding region of protoporphyrinogen oxidase (194).

原卟啉原氧化酶,一种线粒体核黄素蛋白,催化氧依赖氧化原卟啉原Ⅸ至原卟啉Ⅸ,血红素生物合成途径的倒数第二步.原卟啉原氧化酶缺乏导致杂色卟啉症(见OMIM 176200),涉及各种神经精神症状,包括球麻痹、四肢瘫痪和运动神经病变。原卟啉原氧化酶与几种氧化酶有显著的同源性(如单胺氧化酶),含有一个FAD结合基序,在氨基端,Arg59是TRP突变,目前为止,在南非发现的编码前拓扑卟啉原氧化酶的基因中,有一种突变是常见的[由于17世纪荷兰移民的创立者效应],影响FAD结合基序,可能改变原卟啉原氧化酶的FAD结合亲和力。X-连锁铁粒细胞性贫血被认为是一种相似的缺乏症,这种贫血已经被成功地用吡多辛治疗了(见关于吡多辛一节中对ALAS 2的讨论)。一种类似的核黄素补充方法可能有助于治疗那些突变影响原卟啉原氧化酶fad结合区的杂色卟啉病患者。

Electron-transferring-flavoprotein and electron-transferring-flavoprotein ubiquinone oxidoreductase: glutaric aciduria type II and myopathy

电子传递黄素蛋白和电子传递黄素蛋白泛醌氧化还原酶:戊二酸尿和肌病

Electron-transferring-flavoprotein [ETF; which contains an  (see OMIM 231680) and a  βsubunit (see OMIM 130410)] and electron-transferring-flavoprotein ubiquinone oxidoreductase (ETF-QO, see OMIM 231675) are 2 mitochondrial proteins that use FAD coenzymes. The enzymes mediate the transfer of electrons from mitochondrial flavoprotein dehydrogenases (see the discussion of short-chain, medium-chain, and long-chain acyl-CoA dehydrogenases below) to ubiquinone. Metabolic diseases characterized by defects in the mitochondrial oxidation of acyl-CoA esters involved in the metabolism of fatty acids and branched-chain amino acids are often ameliorated by feeding high riboflavin.

电子传递黄素蛋白[ETF;其中包含(见OMIM 231680)β亚组】和电子传递黄素蛋白泛醌氧化还原酶(etf-qo,见omim 231675)是使用FAD辅酶的2种线粒体蛋白。这些酶介导线粒体黄蛋白脱氢酶电子的转移至泛醌(见下文对短链、中链和长链酰基辅酶的讨论)。以酰基辅酶A线粒体氧化缺陷为特征的代谢性疾病参与脂肪酸和支链氨基酸代谢的酯类通常通过喂食高核黄素而得到改善。

Glutaric aciduria II is characterized clinically by hypoglycemia, metabolic acidosis, myopathy, and stridor and biochemically by the accumulation of metabolites, such as glutaric acid. Electron transfer from 9 primary flavoprotein dehydrogenases to the main respiratory chain is impaired in this disease. In most cases, the disorder is due to a deficiency of either ETF or ETF-QO; treatment with oral riboflavin (100–300 mg/d) has been particu-larly effective in a few patients. It has been suggested that increased FAD concentrations might help some patients over-come a defect in coenzyme binding by ETF or ETF-QO (196).

戊二酸尿的临床特征是低血糖,代谢性酸中毒,肌病,以及代谢产物的积累,例如戊二酸。呼吸链上电子传递 的9种主要的黄素蛋白脱氢酶是受损的,在大多数情况下,这种紊乱是由于缺乏ETF或ETF-QO;口服核黄素治疗(100至300毫克/日)在少数患者中特别有效。研究表明,fad浓度的增加可能有助于一些患者克服etf或etf-qo在辅酶结合方面的缺陷。

The crystal structure of human ETF was solved to study 2 mutations seen in patients with glutaric aciduria II:

在2例戊二酸尿患者的研究中,其电子传递黄素蛋白晶体结构缺陷问题被解决
Thr266→Met and  Gly116→Arg, the former being the most common in ETF-deficient patients (197). The structure shows  Thr266 to be within hydrogen-bonding distance of the N-5 of the FAD cofactor; the C-4 carbonyl oxygen of FAD resides in similar proximity to the amide nitrogen of  Thr266 (198). The  Thr266→Met mutant alters the flavin environment. Salazar et al (197) concluded, “The loss of the hydrogen bond at N(5) of the flavin and the altered flavin binding increase the thermodynamic stability of the flavin semiquinone by 10-fold relative to the semiquinone of wild-type ETF.…However, kcat/Km [a measure of catalytic activity] of ETF-QO in a coupled acyl-CoA:ubiquinone reductase assay with oxidized [Thr266→Met] ETF as substrate is reduced 33-fold.”

苏氨酸 266→Met和甘氨酸 116→精氨酸,前者是etf缺乏患者中最常见的。结构显示FAD辅助因子苏氨酸266,与N-5距离氢键结合,FAD的C-4羰基氧,与Thr 266的酰胺氮相似。苏氨酸266→Met突变,在黄素环境下。Salazar 等人得出结论,Flavin在N(5)处氢键的丢失和Flavin结合的改变使Flavin半醌的热力学稳定性提高了10倍相对于野生型ETF的半醌类……然而,以氧化的[Thr 266→Met]ETF为底物的ET-QO在偶联酰基辅酶A中的kcat/kM[催化活性]降低了33倍。

A 29-y-old woman with aciduria who suffered from head-aches, depression, and seizures responded markedly to riboflavin (100 mg/d) (199). Cultured fibroblasts collected before treatment showed residual oxidation of palmitate of between 66% and 52% of control fibroblasts. These investigators concluded, “The biochemical response to riboflavin we observed is consistent with the stabilization of a defective ETF or ETF-QO by increased levels of intramitochondrial FAD” (199). Five ETF-QO mutations identified in four patients with glutaric aciduria II were rare and resulted in a total lack of enzyme activity (200).

一名29岁的妇女患有酸尿症,患有头痛、抑郁和癫痫,对核黄素(100毫克/天)有明显的反应。培养的成纤维细胞在治疗前可见棕榈酸残留氧化,占对照组的66%~52%。这些调查人员得出结论,“我们观察到核黄素的生化反应符合缺陷型ETF的稳定性或etf-qo增加线粒体内fad的水平“

Cell lines from patients with glutaric aciduria II showed significantly lower mitochondrial oxidation of glutarate and ETF activity (201). The addition of FAD increased ETF activity from 4% to 21% of control in a cell line from one patient. The increase in ETF activity in this cell line may have resulted from FAD binding to an ETF apoenzyme with a lowered affinity for the cofactor, thus partially restoring enzymatic activity.

戊二酸尿患者细胞系线粒体氧化戊二酸和etf活性明显降低。FAD的加入使1例细胞株ETF活性由对照组的4%提高到21%。这一细胞系中ETF活性的增加可能是由于FAD与ETF的载脂蛋白酶结合而降低了对辅助性因子的亲和力,从而部分恢复了酶的活性。

A child with brain damage induced by glutaric aciduria II responded to riboflavin therapy at the age of 4 y with consistent and rapid improvement (202). Several other cases of aciduria that responded to riboflavin have been reported in the literature, though the exact enzymatic defect is not always clear (203, 204).

戊二酸尿导致的脑损伤的儿童,4岁时对核黄素治疗有反应和快速改进。其他几例对核黄素有反应的酸尿病例在文献中也有报道,虽然确切的酶缺陷并不总是很清楚

Glutaric aciduria II was assessed through clinical follow-ups in 7 patients, 2 with the neonatal-onset form with congenital anomalies, 3 with the neonatal-onset form without congenital anomalies, and 2 with the late-onset form (205). The neonatal form frequently results in rapid death. All 7 patients received a diet low in fat and protein in addition to oral riboflavin and car-nitine. The results were promising for the late-onset disease, because the 2 children appeared to be growing normally and experiencing complications only with the consumption of food rich in fat or protein. One of the patients with the neonatal-onset form without congenital anomalies responded clinically and bio-chemically to intravenous carnitine (200–300 mg · kg1 · d1) and oral riboflavin (100 mg · kg1 · d1).

对7例戊二酸尿进行了临床随访,2新生儿发病形式伴先天性异常,3新生儿发病形式,无先天性异常,和2例晚发形式,新生儿形态常常导致快速死亡。除口服核黄素和卡尼汀外,所有7例患者均接受低脂低蛋白饮食。结果对于晚发性疾病是有希望的,因为2名儿童似乎在正常生长只有食用富含脂肪或蛋白质的食物才会出现并发症。1例无先天性异常的新生儿起病患者临床上有反应以生物化学方法静脉注射卡尼汀(200~300 mg·kg1·d1)和口服核黄素(100 mg·kg1·d1)。

A 470T→G transversion was identified in the subunit of a patient’s ETF whose cultured cells showed ETF deficiency (206). Reduced ETF was found in the cells despite its being synthe-sized at a normal rate. It was suggested that ETF confers stability on ETF when they bond and that the instability of the mutant ETF could be attributed to its inability to bind with ETF because of drastic conformational changes. In another study, a defect in ETF biosynthesis in a patient with glutaric aciduria II was revealed by pulse labeling techniques (207).

A 470T→G转换在病人的ETF的亚单位中被发现,其培养细胞显示ETF缺乏症。减少的ETF被发现在细胞中,尽管它是同步大小的正常速率。有人认为,etf在与etf结合时会给etf带来稳定性,而变体etf的不稳定性可能是由于其无法与etf结合所致,因为巨大的构象变化。在另一项研究中,用脉冲标记技术揭示了一例戊二酸尿患者ETF生物合成的缺陷。

Peroxisomal glutaryl-CoA oxidase: glutaric aciduria type III Investigation of cultured skin fibroblasts showed that the defect in a girl who responded to riboflavin was in peroxisomal glutaryl-CoA oxidase (see OMIM 231690) and not in ETF or ETF-QO, as in most patients with glutaric aciduria. Glutaric aciduria III in this patient was caused by a peroxisomal rather than by a mitochondr-ial dysfunction (208).

过氧化物酶戊二酰辅酶A:戊二酸尿Ⅲ型培养皮肤成纤维细胞的研究发现,一名对核黄素有反应的女孩的缺陷是过氧化物酶体戊二酰辅酶(见OMIM 231690)而不是ETF或ETF-QO,与大多数戊二酸尿患者一样。戊二酸尿Ⅲ型是由过氧化物酶体引起,而非有丝分裂功能障碍所致。

Short-chain, medium-chain, and long-chain acyl-CoA dehydrogenases: multiple acyl-CoA dehydrogenase deficiency, seizures, and neuromuscular disorders Short-chain (SCAD; butyryl-CoA dehydrogenase), medium-chain (MCAD; acyl-CoA dehydrogenase), and long-chain acyl-CoA dehydrogenases (see OMIM 201470, 201450, and 201460) use FAD to catalyze the first steps in the -oxidation of acyl-CoA substrates, which result in the transfer of electrons to ETF. Defects in the 3 acyl-CoA dehydrogenases, in addition to ETF and ETF-QO defects, have been implicated in multiple acyl-CoA dehydrogenase deficiency. All 5 are mitochondrial proteins. The resulting urinary accumulation of ethylmalonate, methylsucci-nate, and butyrylglycine is associated with neuromuscular dys-function and seizures.

短链、中链和长链酰基辅酶A脱氢酶:多种酰基-辅酶A脱氢酶缺乏、癫痫发作和神经肌肉疾病短链(SCAD;丁酰-CoA脱氢酶),中链(mcad;酰基-coa脱氢酶)和长链酰基-coA脱氢酶(见OMIM 201470、201450和201460)利用FAD催化酰基-CoA底物氧化的第一步,导致电子向ETF转移。3-酰基-CoA脱氢酶中的缺陷,除ETF和ETF-QO缺陷外,涉及多个acyl-CoA脱氢酶缺乏。所有5种都是线粒体蛋白。由此产生的尿路积乙丙二酸、丁二酸甲酯和丁酸甘氨酸与神经肌肉功能障碍和癫痫发作有关。

Epileptic seizures were reported in a child carrying a Gly209→Ser mutant SCAD, resulting from the DNA mutation 625G→A (209). This SCAD polymorphism has been postulated to lower FAD affinity and occurs in 35% of individuals (AA = 4% of control population, AG = 31% of control popula-tion). The symptoms disappeared, with rapid and permanent improvement of the child’s condition, with the administration of 25 mg riboflavin/kg, later lowered to 10 mg · kg1 · d1. The authors speculated that the amino acid change affects the folding efficiency of the variant SCAD or influences the interaction of SCAD with its FAD cofactor.

据报道,一名携带Gly 209→Ser突变体的儿童癫痫发作,由625 g→A突变引起的。这种SCAD多态性被认为降低了fad亲和力,并在35%的个体中发生。(AA=对照种群的4%,AG=对照种群的31%。)随着儿童病情的迅速和永久改善,症状消失,注射核黄素25 mg/kg,随后降至10 mg·kg1·d1。推测氨基酸的变化影响变异体SCAD的折叠效率,或影响SCAD与FAD辅助因子的相互作用。
In another case report, SCAD and MCAD activities were 35% of normal in a 12-y-old girl (210). Western blot analysis showed the absence of SCAD and decreased MCAD but normal amounts of ETF. Although unresponsive to carnitine, the patient showed a marked improvement with 100 mg riboflavin/d with a concomitant normalization of SCAD activity and a reappearance of SCAD protein in Western blots. MCAD activity and protein amounts remained low. It is possible that a mutation decreased the stability and that riboflavin increased enzyme stability. Although it is also possible that the patient had an altered riboflavin metabolism resulting in lower mitochondrial FAD concentrations, the authors speculated that “the different effects of riboflavin deficiency on SCAD, MCAD, and possibly ETF and [ETF-QO] could be explained by the different affinities of FAD for the flavoprotein apoenzymes” (210). An FAD-related acyl-CoA dehydrogenation defect was also suspected in a patient with MCAD and SCAD deficiency who responded to 3   100 mg riboflavin/d (211).

在另一个案例中,在一个12岁的女孩中,SCAD和MCAD活动是正常人的35%。Westernblot分析显示,未见SCAD,MCAD降低,但ETF正常。虽然对肉毒碱没有反应,但患者服用100毫克核黄素/日后症状明显改善,SCAD活性也随之恢复正常并在重现SCAD蛋白印记。MCAD活性和蛋白质含量较低。有可能是突变降低了稳定性,核黄素提高了酶的稳定性。虽然病人的核黄素代谢也可能发生改变,导致线粒体fad浓度降低,作者推测“核黄素缺乏对SCAD的不同影响,mcad,也可能是etf和[etf-qo],可以用FAD对风味蛋白载脂蛋白酶的不同亲缘关系来解释。一名MCAD和SCAD缺乏症患者也怀疑与时尚有关的酰基辅酶A脱氢缺陷,他对3100毫克核黄素/日有反应。

An 11-mo-old boy with a mild variant of multiple acyl-CoA dehydrogenase deficiency (ethylmalonic-adipic aciduria) received 200 mg riboflavin/d, leading to dramatic clinical improvement with a restoration of normal respiration and an increase in muscu-lar tone within 2 mo (212). Riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency was confirmed in cultured fibroblasts, which showed increased enzymatic activity in the presence of 1 g riboflavin/L (265 nmol/L).

一名11岁男孩患有轻度的酰基-辅酶A脱氢酶缺陷(乙基丙二酸尿),每天服用200毫克核黄素,在2mo内恢复正常呼吸和增加肌肉张力,使临床有了显著的改善。培养成纤维细胞核黄素反应多酰基辅酶A脱氢酶缺陷,当核黄素浓度为1 g/L(265 nmol/L)时,酶活性增强。

Another case report described a male infant diagnosed with multiple acyl-CoA dehydrogenase deficiency who exhibited marked improvement through the administration of riboflavin (100 mg/d) and Lcarnitine (1000 mg/d) (213). The child showed normal development (up to the age of 10 y) and was suspected of harboring an ETF-QO deficiency, although defects in SCAD, MCAD, and long-chain acyl-CoA dehydrogenase could also be responsible.

另一例报告描述一名男婴被诊断为多个酰基-辅酶A脱氢酶缺乏症组织通过服用核黄素(100毫克/天)和肉碱(1000毫克/天),表现出明显的改善。这名儿童显示出正常的发育(10岁),并被怀疑患有ETF-QO缺陷,虽然SCAD、MCAD和长链酰基-CoA脱氢酶的缺陷也可能是原因之一.

TABLE 4 Enzymes that use a thiamine pyrophosphate (TPP) cofactor1
Defective enzyme and EC no.
Localization
Reaction catalyzed
Disease or condition
OMIM no.
Inheritance
Branched-chain _x0007_-ketoacid dehydrogenase
支链-酮酸脱氢酶
(1.2.4.4)
Mitochondrial matrix
线粒体基质
_x0007_α-Keto acids → acyl-CoA + CO2
Maple syrup urine disease (branched-chain ketoaciduria) and buildup of BCAAs (leucine, isoleucine, and valine) in blood and urine
枫糖尿病(支链酮酸尿)、血和尿液中BCAA(亮氨酸、异亮氨酸和缬草碱)的积累
248600
Autosomal recessive
常染色体隐性
Pyruvate decarboxylase (4.1.1.1)
丙酮酸脱羧酶
Mitochondrial matrix
线粒体基质
Pyruvate → acetyl-CoA + CO2
Leigh disease and lactate and pyruvate buildup in serum
利氏病与血清乳酸和丙酮酸的升高
312170
X-linked
伴X染色体的
Thiamine transporter SLC19A2
硫胺素转运体SLC19A2
Integral membrane protein
整体膜蛋白
[size=9.0000pt]—
Megaloblastic anemia, diabetes mellitus, and sensorineural deafness
巨幼细胞性贫血,糖尿病,和感音神经性聋
603941
Autosomal recessive
常染色体隐性
Thiamine pyrophosphokinase (2.7.6.2)
硫胺素焦磷酸激酶
Cytoplasmic?
细胞质的
ATP + thiamine → AMP + TPP
Megaloblastic anemia, diabetes mellitus, and sensorineural deafness
巨幼细胞性贫血,糖尿病,和感音神经性聋
606370
Autosomal recessive
常染色体隐性
_x0007_α-Ketoglutarate dehydrogenase
α-酮戊二酸脱氢酶
(1.2.4.2)
Mitochondrial matrix
线粒体基质
_x0007_α-Ketoglutarate + CoA + NAD →succinyl-CoA + CO2 + NADH
Megaloblastic anemia, diabetes mellitus, and sensorineural deafness
巨幼细胞性贫血,糖尿病,和感音神经性聋
203740
Autosomal recessive
常染色体隐性
1 BCAA, branched-chain amino acid; OMIM, Online Medelian Inheritance in Man (4).


TABLE 5 Enzymes that use an FAD or FMN (riboflavin) cofactor1 使用fad或FMN(核黄素)cofactor 1的酶
Defective enzyme and EC no.
Localization
Reaction catalyzed
Disease or condition
OMIM no.
Inheritance
Methylenetetrahydrofolate reductase
亚甲基四氢叶酸还原酶
(NADPH) (1.5.1.20)
Cytoplasmic
细胞质的
5,10-Methylene-THF + NADPH → 5-methyl-THF + NADP
Homocystinemia, 高胱氨酸血,cardiovascular disease,migraine, diabetic nephropathy,and congenital cardiac malformations
心血管疾病,偏头痛糖尿病肾病,先天性心脏畸形
236250
Autosomal recessive
常染色体隐性
NAD(P):quinone oxidoreductase 1 (1.6.99.2)
Cytoplasmic细胞质
Reduction of quinones and quinonoid compounds to hydroquinones
醌类化合物向氢醌类化合物的转化
Risk of leukemia and urothelial tumor
白血病和尿路上皮肿瘤的风险
125860
Autosomal recessive常染色体隐性
Protoporphyrinogen oxidase
原卟啉原氧化酶;
(1.3.3.4)
Bound to inner mitochondrial membrane
与线粒体内膜结合
Protoporphyrinogen IX + O2 →protoporphyrin IX + H2O2
Variegate porphyria and neuropsychiatric complications, including motor neuropathy
杂色卟啉症,神经精神并发症,运动神经病
176200
Autosomal dominant
常染色体显性
Electron-transferring-flavoprotein and electron-transferring-flavoprotein ubiquinone oxidoreductase (1.5.5.1)
Inner mitochondrial membrane (ETF-QO)
线粒体内膜
Electron flow: reduced acyl-CoAdehydrogenases → ETF → ETF-QO
Glutaric aciduria type II, myopathy, metabolic acidosis, and hypoglycemia
戊二酸尿II型,肌病代谢性酸中毒低血糖
231680,231675
Autosomal recessive
常染色体隐性
Peroxisomal glutaryl-CoA oxidase
过氧化物酶体戊二酰辅酶A氧化酶
Peroxisomal
过氧化物酶
[size=9.0000pt]
Glutaric aciduria type III
戊二酸尿Ⅲ型
231690
Autosomal recessive
常染色体隐性
Short-chain, 短链,medium-chain,中链, and long-chain long-chain
acyl-CoA dehydrogenases
酰基辅酶A脱氢酶
(1.3.99.2, 1.3.99.3,and 1.3.99.13)
Mitochondrial matrix
线粒体基质
Acyl-CoA + ETF → 2,3-dehydroacyl-CoA + reduced
ETF
[size=9.0000pt]
Multiple acyl-CoA dehydrogenase deficiency,seizures, failure to thrive, metabolic acidosis,and neuromuscular disorders
多酰基辅酶A脱氢酶缺乏症、癫痫发作,不能茁壮成长,代谢剂和剂量,神经肌肉疾病
201470,201450, 201460
Autosomal recessive
常染色体隐性
Mitochondrial complex I (1.6.5.3)
线粒体复合体I
Mitochondrial membrane
线粒体酶,线粒体膜
Electron transport enzyme
电子转运酶
Complex I deficiency and myopathy
复杂I型缺乏症与肌病
252010
Autosomal recessive
常染色体隐性
Complex I (mitochondrial transfer RNA Leu mutations)
复合体I(线粒体转移RNA 亮氨酸突变 )
Mitochondrial membrane
线粒体酶
Electron transport enzyme
电子转运酶
Complex I deficiency and MELAS
复杂I缺陷与MELAS
590050
Mitochondrial
线粒体
1 ETF, electron-transferring-flavoprotein dehydrogenase; ETF-QO, electron-transferring-flavoprotein ubiquinone oxidoreductase; MELAS, mitochondrial encephalomyopathy, lactic acidosis, and stroke-
like episodes; OMIM, Online Mendelian Inheritance in Man (4); THF, tetrahydrofolate.


Mitochondrial complex I: myopathy Defects in mitochondrial complex I [NADH dehydrogenase (ubiquinone)] cause myopathies (see OMIM 252010). Decreased affinity for the FMN cofactor may explain the cases of riboflavin responsiveness.

线粒体复合体I:线粒体复合物Ⅰ型肌病缺陷【还原型烟酰胺腺嘌呤二核苷酸,还原型辅酶I】与FMN辅助因子的亲和力降低可能是核黄素应答的原因之一。

In 5 patients with a mitochondrial myopathy associated with a complex I deficiency, riboflavin (35–60 mg/d) was effective in 3 patients, with a normalization of enzymatic activity (214). In cultured fibroblasts from a patient with an Arg228→Gln mutation in the complex I subunit encoded by the nuclear NDUFS2 gene, the addition of riboflavin was able to significantly increase ATP production (215). Because the NDUFS2-encoded protein does not contain an FMN binding site, it was suggested that the mutation either interfered with the interaction between a flavo-protein and FMN or that riboflavin has a general stabilizing effect on complex I. In a survey of 9 patients with complex I deficiency, the myopathy of 1 patient dramatically improved dur-ing treatment with riboflavin (9 mg/d) and L-carnitine (216). Complex I activity rose 17-fold to normal levels after 7 mo of therapy. Several other cases of riboflavin-responsive complex I myopathies have likewise been reported (217, 218).

5例线粒体肌病合并复杂I型缺乏症,核黄素(35~60 mg/d)有效3例,酶活性正常。在培养的成纤维细胞中,NDUFS 2基因编码的复杂I亚基存在Arg 228→Gln突变,核黄素的加入能显著提高ATP的产量。因为NDUFS 2编码的蛋白质不包含FMN结合位点,结果表明,该突变或干扰了黄酮蛋白与FMN的相互作用,或核黄素对配合物I具有一般的稳定作用。在对9例复杂I型缺乏症患者的调查中,1例肌病明显改善了核黄素(9mg/d)和L-肉碱的治疗效果。治疗7mo后,复合物I活性提高17倍,降至正常水平。另外几例核黄素应答复合物Ⅰ型肌病也有报道。

Mitochondrial defects were analyzed in 3 patients from a large consanguineous family and in 1 unrelated patient who all had exercise intolerance since early childhood and complex I deficiencies (218). Supplementation with 100 mg riboflavin/d resolved many clinical complications. A biopsy taken in one of the patients after 2 y of riboflavin therapy showed an increase in complex I activity from 16% to 47% of control.

3例大血亲家系线粒体缺陷分析在1例无血缘关系的患者中,他们从小就有运动不耐受和复杂的I型缺陷。添加100 mg核黄素/d可缓解临床并发症。其中一位患者在接受核黄素治疗2y后的活检显示复合I活性从对照组的16%提高到47%。

Mitochondrial transfer RNA leucine (UUR): complex I deficiency, MELAS syndrome, migraine, and myopathy A 32-mo-old patient with a complex I deficiency, an associated myopathy, and a 3250T→C mutation in the gene for mitochondr-ial transfer RNA (tRNA) leucine (UUR) (see OMIM 590050; also discussed in the section on niacin) had a sustained clinical response to riboflavin (50 mg/d) (219). The authors refer to reports of riboflavin being effective in 11 patients with complex I deficiency, although the underlying cause was not known in these cases. Another patient with a mutation (3243A→G) in the same mitochondrial gene for tRNA leucine (UUR), who initially pre-sented with MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome at age 19, had pre-viously responded to a mixture of riboflavin and nicotinamide, although the vitamins were not tested individually (220).

线粒体转移RNA亮氨酸(UUR):复杂I型缺乏症,梅拉斯综合症,偏头痛和肌病一位32岁的复杂I型缺乏症患者,一种相关的肌病,线粒体转移RNA基因的3250 T→C突变(TRNA)亮氨酸(UUR)(见OMIM 590050;也在关于烟酸的一节中讨论)对核黄素(50毫克/天)有持续的临床反应。作者提到了11例复杂I型缺乏症患者核黄素有效的报道,尽管在这些病例中根本原因尚不清楚。另一例trna亮氨酸线粒体基因突变(3243 3A→G)的患者,他们最初接受了mLAS治疗。(线粒体脑肌病、乳酸酸中毒和中风样发作)在19岁的时候,曾经对核黄素和烟酰胺的混合物有反应,尽管没有单独测试维生素。

Thirteen electron transport chain proteins are coded for and synthesized in the mitochondria, of which 7 contribute to complex I. If the tRNA mutations incur a poor fidelity of leucine incorporation during mitochondrial translation, it is plausible that complex I would be more prone to defects than would other complexes. Another possible explanation for the specific complex I defect is that there is a critical leucine in a cofactor binding site of complex I that is incorporated into the complex I peptide with only moderate fidelity. FMN is an important cofactor for complex I, which could explain why riboflavin responsiveness has been reported in patients with these tRNA mutations.

在线粒体中编码并合成13个电子传输链蛋白,其中7个对I复合物有贡献。如果tRNA突变在线粒体翻译过程中导致亮氨酸掺入的保真度差,这是合理的,复杂,我会更容易出现缺陷,比其他复合物。另一个可能解释特定配合物I缺陷的原因是,配合物I的辅助因子结合位点中存在一个关键的亮氨酸,它被结合到只有mo的复合物I肽中。降低忠诚度。FMN是复杂I的一个重要的辅助因子,这可以解释为什么有这些tRNA突变的患者出现核黄素反应。

Of the 3 mitochondrial encephalomyopathies [MELAS, myoclonus epilepsy associated with ragged-red fibers (MERRF), and chronic progressive external ophthalmoplegia (CPEO)] the mitochondrial mutation 3243A→G appears to be specific to MELAS patients; it was found in 26 of 31 MELAS patients and in 1 of 29 CPEO patients and was absent in 5 MERRF patients and 50 control subjects (221). Migraine can be a prominent fea-ture in patients affected by mitochondriopathies such as MELAS syndrome and has been treated with high doses of riboflavin (169; see also the discussion of MTHFR above).

线粒体脑肌病的3种[MELAS,肌肉阵发性癫痫与粗糙的红色纤维(MERRF),及慢性进行性外眼肌麻痹(CPEO)]线粒体突变3243 3A→G可能是特异性的MELAS患者;在31例MELAS患者中有26例和29例CPEO患者中有1例未发现,在5例MERRF患者和50例正常人中未发现。偏头痛是线粒体病(如MELAS综合征)患者的突出表现,并已接受大剂量核黄素治疗。

Methionine synthase reductase: homocystinuria and mental retardation
See the discussion in the section on cobalamin.
Dihydrolipoamide dehydrogenase: lactic acidosis See the discussion in the section on lipoic acid.

蛋氨酸合成酶还原酶:高胱氨酸尿和智力迟钝
二氢硫辛酰胺脱氢酶:乳酸酸中毒见关于硫辛酸一节的讨论

Tissue concentrations and toxicity 组织浓度和毒性
No UL has been defined for riboflavin intake because there have been few reports of adverse effects with doses in the hun-dreds of milligrams (7). A migraine study mentioned above recorded 2 adverse effects of 400 mg riboflavin/d—diarrhea and polyuria—in 2 of 28 patients (169).

核黄素的摄入量没有UL的定义,因为很少有关于剂量在毫克中的不良影响的报道。上述偏头痛研究记录了28例400毫克核黄素/d腹泻和多尿症的2种不良反应。

The rate of absorption of riboflavin is proportional to intake and increases when riboflavin is ingested along with other foods (7). In a small group of cirrhosis patients, a single 40-mg oral dose of riboflavin was shown to raise plasma riboflavin 13.7-fold and flavocoenzymes 1.4-fold over baseline (222). A randomized clinical trial determined that the maximum amount of riboflavin that can be absorbed from a single oral dose is 27 mg for adults (223). Thus, the percentage of high doses of vitamins that is actually taken up in plasma or cells depends strongly on mode and fre-quency of dosage delivery.

核黄素的吸收率与摄取量成正比,当核黄素与其他食物一起食用时,吸收率增加。在一小群肝硬化患者中,单次口服40毫克核黄素可使血浆核黄素和黄酶比基线水平提高13.7倍和1.4倍。一项随机的临床试验确定成人一次口服可吸收核黄素的最大量为27毫克。因此,在血浆或细胞中摄取的高剂量维生素的百分比很大程度上取决于投药的方式和频率。

NIACIN (VITAMIN B-3) 烟酸 (维生素B-3)

The DRI for niacin is 16 mg niacin equivalents/d for men and 14 mg equivalents/d for women (7), where 1 niacin equivalent is 1 mg niacin obtained through the diet or the metabolism of tryptophan. The term niacin is often used synonymously with nicotinic acid. Nicotinamide, the amide form of nicotinic acid, is a building block for both nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) (7). Rossmann folds are  strands connected by  helix crossover elements and compose nucleotide binding sites. They appear to be the most important structure for NAD(P) binding in at least one group of NAD(P)-dependent proteins. Common motifs include the GxxxGxG phosphate binding pattern of glycines (where x is any amino acid), a ribose binding aspartate, and a nicotinamide-ribose binding YxxxK motif. The adenine binding motif found in many FAD binding proteins was found in only a few NAD(P) binding proteins (150). The following NAD-dependent enzymes are summarized in Table 6.

烟酸的DRI为16mg烟酸当量/d,女性为14mg当量/d,其中,1烟酸当量为1毫克烟酸,可通过饮食或色氨酸的代谢得到。烟酸一词常与尼克酸同义词使用。烟酰酸,烟酸的酰胺形式,是烟酰胺腺嘌呤二核苷酸(NAD)和磷酸烟酰胺腺嘌呤二核苷酸(NADP)的基石。Rossmann褶皱是由螺旋线交叉元件连接的一条线并组成核苷酸结合位点。它们似乎是NAD(P)在至少一组依赖于NAD(P)的蛋白质中结合的最重要的结构。常见的基序包括葡萄糖的GxxxGxG磷酸结合模式(其中x是任何氨基酸),一种核糖结合的天冬氨酸和烟酰胺-核糖结合的YxxxK基序。在许多FAD结合蛋白中发现的腺嘌呤结合基序仅存在于少数NAD(P)结合蛋白中。表6概述了下列NAD依赖的酶.

Mitochondrial aldehyde dehydrogenase (NAD+): alcohol intolerance and flushed face in Asians, alcohol-induced vasospastic angina, Alzheimer disease, and oral, esophageal, and stomach cancer

线粒体醛脱氢酶 (NAD+):亚洲人对酒精的不容忍和脸红,酒精引起的血管紧张性心绞痛,阿尔茨海默病、口腔癌、食道癌和胃癌

Mitochondrial aldehyde dehydrogenase (NAD+) (ALDH2) catalyzes the NAD-dependent oxidation of acetaldehyde, which is formed by the oxidation of ethanol by alcohol dehydrogenase (see OMIM 100650). The single genetic factor most strongly correlated with reduced alcohol consumption and incidence of alcoholism is the naturally occurring variant of ALDH2, which contains a Glu487→Lys substitution. The Lys487 allele of ALDH2 (also called ALDH2*2) is found in 50% of the Asian population and is associated with a phenotypic loss of ALDH2 activity in both heterozygotes and homozygotes. ALDH2-deficient individuals exhibit an adverse response to ethanol consumption, which is probably caused by elevated concentrations of blood acetalde-hyde (224). The Glu487→Lys variant has been shown to exhibit a 150-fold increase in Km for its NAD cofactor (225).

线粒体醛脱氢酶(NAD)(ALDH 2)催化乙醛的NAD依赖氧化,乙醇由乙醇脱氢酶氧化而成 (see OMIM 100650). 与减少饮酒和酗酒发生率密切相关的单一遗传因素是自然发生的ALDH 2变异体,其含有Glu487或Lys取代。在50%的亚洲人群中发现了ALDH 2的Lys 487等位基因(又称ALDH 2*2)与杂合子和纯合子ALDH 2活性的表型丧失有关。ALDH 2缺乏的个体对乙醇消费表现出不良反应,这可能是由于血中乙酰丙氨酸-海德浓度升高所致。Glu487或Lys变体已显示出其NAD辅因子的Km增加了150倍。

High blood acetaldehyde is potentially carcinogenic and neu-rotoxic, and the correlation between Glu487→Lys and several cancers has been well established: deficient ALDH2 activity due to the polymorphism has been associated with oral cancer, esophageal cancer, stomach cancer, Alzheimer disease, and alco-hol-induced vasospastic angina.

高血乙醛具有潜在的致癌性和新毒性,Glu 487→Lys与几种癌症之间的相关性已经得到了很好的证实:ALDH 2基因多态性导致的ALDH 2活性缺失与口腔癌有关,食管癌,胃癌,阿尔茨海默病,以及铝引起的血管紧张性心绞痛。

ALDH2 and glutathione transferase M 1 polymorphisms were studied in 191 patients with oral cancer and in 121 control subjects without oral cancer who had a history of alcohol use (226). The incidences of inactive ALDH2 and glutathione transferase M 1 in the cancer group with an alcohol-drinking habit were 34.2% and 67.5%, higher than in the noncancer group with an alcohol-drinking habit (15.1% and 45.5%, respectively). Another study found the ALDH2*2 allele to be overrepresented in Japan-ese alcoholics with esophageal, stomach, and oropharyngolaryn-geal cancers (227), further illustrating the risk of developing cancer in individuals harboring the variant ALDH2 enzyme.

191例口腔癌患者ALDH 2和谷胱甘肽转移酶M1多态性的研究在121名无口腔癌病史的对照组中,他们有饮酒史。有饮酒习惯的癌症组ALDH 2和谷胱甘肽转移酶M1的发生率分别为34.2%和67.5%,有饮酒习惯的非癌症组高于非癌症组(分别为15.1%和45.5%)。另一项研究发现,ALDH 2*2等位基因在伴有食道癌、胃癌和口咽管癌的日本酗酒者中过度表达。进一步说明携带变异ALDH 2酶的人患癌症的风险。

The polymorphism is also a risk factor for late-onset Alzheimer disease. The frequency of the ALDH2*2 allele is 48.1% in late-onset Alzheimer disease patients (n = 447) com-pared with 37.4% in control subjects matched by sex, age, and region (P = 0.001) (228). The added risk was present in both men (P = 0.01) and women (P = 0.02). In addition, the APOE*E4 allele of the apolipoprotein E gene was confirmed as an inde-pendent risk factor for late-onset Alzheimer disease (P = 0.002). The odds ratio for late-onset Alzheimer disease in carriers of the ALDH2*2 allele was almost twice that in noncarriers. Among patients homozygous for the APOE*E4 allele, the age at onset of late-onset Alzheimer disease was significantly lower in those with than in those without the ALDH2*2 allele. In addition, dosage of the ALDH2*2 allele significantly affected age at onset of patients homozygous for the APOE*E4 allele. It would be of interest to determine whether long-term niacin use could prevent or delay the onset of Alzheimer disease or relieve present Alzheimer disease in patients with the polymorphism.

多态也是迟发性阿尔茨海默病的危险因素.迟发性阿尔茨海默病患者中ALDH 2*2等位基因频率为48.1%(n=447),与按性别、年龄和区域匹配的对照组的37.4%相比,差异有显着性(P=0.001)。男性(P=0.01)和女性(P=0.02)都有增加的风险。此外,载脂蛋白E基因的APOE*E4等位基因被证实为迟发性阿尔茨海默病的独立危险因素(P=0.002)。ALDH 2*2等位基因携带者迟发性阿尔茨海默病的优势比几乎是非携带者的两倍。在APOE*E4等位基因纯合子患者中,有ALDH 2*2等位基因者晚发性阿尔茨海默病发病年龄明显低于无ALDH 2*2等位基因者。此外,ALDH 2*2等位基因的剂量显著影响APOE*E4等位基因纯合患者的发病年龄。长期使用的烟酸是否可以预防或延缓阿尔茨海默病发作或缓解多态性患者中的阿尔茨海默病的研究将会非常有意义。

TABLE 6 Enzymes that use an NAD or NADP (niacin) cofactor 1
有兴趣确定长期使用的烟酸是否可以预防或延缓阿尔茨海默病发作或缓解多态性患者中的阿尔茨海默病。

Defective enzyme and EC no.
Localization
Reaction catalyzed
Disease or condition
OMIM no.
Inheritance
Aldehyde dehydrogenase
醛脱氢酶
(NAD+) (1.2.1.3)
Mitochondrial matrix
线粒体基质
Aldehyde + NAD + H2O → acid + NADH
Cancer risk from high blood acetaldehyde
高血乙醛对癌症的危险
100650
Autosomal dominant
Glucose-6-phosphate 1-dehydrogenase (1.1.1.49)
葡萄糖-6-磷酸1-脱氢酶
Cytoplasmic
细胞质
Glucose-6-phosphate + NADP →6-phosphogluconolactone + NADPH
Oxidation-induced hemolytic anemia, favism
氧化引起的溶血性贫血,豆类中毒,蚕豆病
305900
X-linked
6-phosphogluconolactone + NADPH
Complex I
6-磷酸葡萄糖醛酸内酯+NADPH复合物Ⅰ
(mitochondrial transfer RNA mutations)
(线粒体转移RNA突变)
(1.6.5.3)
Mitochondrial
Membrane
线粒体的薄膜
Electron transport enzyme
电子转运酶
Complex I deficiency, elevated blood lactate,and pyruvate
复合物I缺乏、血乳酸和丙酮酸升高
590050
Mitochondrial
[size=9.0000pt]
线粒体的
Dihydropteridine reductase (1.6.99.7)
二氢喋啶还原酶
Cytoplasmic?
细胞质
NAD(P)H + BH2 → NAD(P) + BH4
Phenylketonuria II, hyperphenylalaninemia,and cognitive dysfunction
苯丙酮尿症Ⅱ、高苯丙氨酸血症和认知功能障碍
261630
Autosomal recessive
常染色体隐性
Long-chain-3-hydroxyacyl-CoA dehydrogenase
长链3-羟酰CoA脱氢酶类
(1.1.1.211)
Mitochondrial matrix
3-Hydroxyacyl-CoA + NAD → 3-oxoacyl-CoA + NADH
-Oxidation defect, hypoglycemia,cardiomyopathy, and sudden death
低血糖、心肌病和猝死
600890
Autosomal
1 BH
2, dihydrobiopterin; BH4, tetrahydrobiopterin; OMIM, Online Mendelian Inheritance in Man (4).

Alcohol ingestion induced anginal attacks in 16 of 66 patients without the Glu487→Lys mutation, in 8 of 22 heterozygotes, and in 1 of 3 patients homozygous for the mutation (229). The intervals between alcohol ingestion and the onset of attacks were shorter in ALDH2*2 homozygotes (0.17 h) and heterozygotes (1.5 ± 0.6 h) than ALDH2*1 (ie, Glu487 allele) homozygotes (5.4 ± 0.6 h). The amount of ethanol that induced the attacks was significantly greater in control subjects (96.1 mL) than in ALDH2*2 homozygotes (11 mL) and heterozygotes (42.5 mL). Although the frequency of anginal attacks induced by alcohol ingestion did not differ between the ALDH-deficient and normal homozygotes, anginal attacks were induced in the ALDH-deficient patients by a smaller amount of alcohol. Thus, niacin intake may help to ameliorate some of the deleterious effects of alcohol con-sumption such as anginal attacks.

66例无Glu487→Lys突变的患者中,16例因酒精摄入引起的心绞痛发作,在22个杂合子中有8个,其中1例为纯合子突变(229).ALDH 2*2纯合子(0.17h)和杂合子(1.5±0.6h)与ALDH 2*1(Glu487等位基因)纯合子(5.4±0.6h)相比,摄入酒精的间隔时间缩短。对照组(96.1 mL)的乙醇量显著高于ALDH 2*2纯合子(11 ML)和杂合子(42.5 mL)。虽然ALDH缺乏的纯合子和正常的纯合子因酒精摄入引起的心绞痛发作的频率没有差别,在ALDH缺乏的患者中,少量酒精会引起心绞痛发作.因此,烟酸的摄入可能有助于改善酒精摄入的一些有害影响,如心绞痛袭击。

With use of concentrations of the glycated hemoglobin as an assay, the Glu487→Lys polymorphism was also suggested to be a risk factor for hyperglycemia in persons with diabetes (230, 231). However, the acetaldehyde adduct of hemoglobin may cochro-matograph with glycated hemoglobin and has not been ruled out as the cause of the findings. The amount of hemoglobin adducts formed is a function of the concentration and number of expo-sures to acetaldehyde (232).

用糖化血红蛋白的浓度作为测定,Glu487→Lys多态性也被认为是糖尿病患者高血糖的危险因素。然而,血红蛋白的乙醛加合物可能与糖化血红蛋白进行耳蜗造影术,尚未被排除为该结果的原因。所形成的血红蛋白加合物的数量与乙醛的浓度和数量有关。

A significant genetic difference was found in the ALDH2 gene between a group of Japanese patients with alcoholic pancreatitis and control subjects (233). The frequency of the ALDH2*1 allele was found to be 0.681 and that of the ALDH2*2 allele to be 0.319 in the control subjects; these values were 0.935 and 0.065 in the patients, respectively. Most of the patients (27 of 31) were ALDH2*1/2*1, only 4 were ALDH2*1/2*2, and none of the patients were ALDH2*2/2*2. These results indicate that genetic polymorphism of the ALDH2 gene decreases the risk of becom-ing an alcoholic and hence getting pancreatitis.

一组日本酒精性胰腺炎患者的ALDH 2基因与对照组相比有显著的遗传差异。对照组ALDH 2*1等位基因频率为0.681,ALDH 2*2等位基因频率为0.319;这些值分别为0.935和0.065。大多数患者(31人中27人)为ALDH 2*1/2*1,只有4人为ALDH 2*1/2*2,所有患者均为ALDH2*2/2*2。这些结果表明,ALDH 2基因的遗传多态性降低了酒精性胰腺炎的风险。

The Glu487→Lys polymorphism results in an ALDH2 enzyme with 8% enzymatic activity (234) and a 150-fold increased Km for NAD (225). Administration of nicotinic acid (235) or nicotinamide (236), which have been shown to increase intracellular NAD concentrations, might reverse or prevent the carcinogenic and other effects of the polymorphism. A 6-y case-control study in Italy with > 1000 participants found niacin intake to be inversely correlated with esophageal cancer risk (237). Similar investigations might be done on a population of Asian descent.

Glu487→Lys多态性导致ALDH 2酶活性仅仅为8%,而NAD使得其KM增加了150倍。烟酸或烟酰胺,已经被证明能增加细胞内NAD的浓度,可能逆转或防止多态的致癌和其他影响。意大利一项为期6个月的病例对照研究发现,烟酸摄入量与食管癌风险成反比关系。可以对亚裔人口进行类似的调查。
Glucose-6-phosphate 1-dehydrogenase: hemolytic anemia and favism
葡萄糖-6-磷酸脱氢酶:溶血性贫血与蚕豆病

Glucose-6-phosphate 1-dehydrogenase (G6PD; see OMIM 305900) is an X-linked cytosolic enzyme that generates NADPH in the oxidative branch of the pentose phosphate pathway. Reduced NADPH is a key electron donor in reductive biosyn-thetic reactions and in the defense against oxidizing agents, possibly through the maintenance of reduced glutathione con-centrations. Additionally, G6PD expression is enhanced by gen-eral oxidative stress (238).

葡萄糖-6-磷酸1-脱氢酶(G6PD;见OMIM 305900)是一种X-连接的胞浆酶,在磷酸戊糖途径的氧化分支中产生NADPH。还原NADPH是还原生物合成反应中的一个关键电子供体,也是防御氧化剂的关键电子供体,可能是通过维持还原型谷胱甘肽的浓度。此外,g6pd的表达也被氧化应激所增强。

G6PD is one of the most polymorphic enzymes and G6PD deficiency is the single most common metabolic disorder, with an estimated 400 million persons thought to be affected world-wide (239). This is because many defects in conserved regions of G6PD, which result in a reduced enzyme activity, confer an increased resistance to malarial infection. Although some forms of G6PD deficiency are asymptomatic, others result in neonatal jaundice, chronic nonspherocytic anemia, acute episodic hemolytic anemia (caused by oxidative stress such as ingestion of fava beans), drug-induced hemolysis, and hemolysis induced by infections. A mild phenotype, characterized by neonatal jaun-dice, favism, and hemolytic anemia, has become common in the world (240), arising in regions of past malaria risk such as Africa, India, the Mediterranean, and Southeast Asia (241).

G6PD是最多态的酶之一,G6PD缺乏症是最常见的代谢紊乱,估计有4亿人被认为受到世界范围的影响。这是因为G6PD的守恒区有很多缺陷,这导致酶活性降低,增加了对疟疾感染的抵抗力。虽然某些形式的G6PD缺乏症是无症状的,其他则导致新生儿黄疸、慢性非球形贫血、急性间歇性溶血性贫血(由氧化应激引起,例如进食蚕豆),药物引起的溶血和感染引起的溶血。以新生儿JAUN-DICE、FADVISM和溶血性贫血为特征的轻度表型在世界变得普遍。出现在过去疟疾风险地区,如非洲、印度、地中海和东南亚。

G6PD mutations compromise the body’s ability to protect against oxidative stress, as shown by the hemolytic response by many deficient individuals to fava beans, which are known to contain the oxidants vicine and divicine. Red blood cells in particular are susceptible to lysis mediated by oxidative stress because of their lack of mitochondria and subsequent reliance on G6PD and one other pentose phosphate pathway enzyme for the production of NADPH. Tobacco smoke is known to contain sev-eral oxidants (242) and may be a source of deleterious oxidative stress on persons around the world who are G6PD deficient. Because at least one common variant of G6PD has been shown to have a decreased binding affinity for NADP, it might follow that nicotinic acid or nicotinamide administration to raise intra-cellular NAD and NADP concentrations would strengthen the body’s reductive capacity and reverse the deleterious effects of the deficiency. Although NAD concentrations have been shown to be increased by high concentrations of nicotinic acid (235) and nicotinamide (236), NADP concentrations do not appear to have been examined.

G6PD突变会损害机体抵御氧化应激的能力,正如许多缺陷个体对蚕豆的溶血反应所显示的,其中含有氧化剂维辛和狄维辛。红细胞尤其容易受到氧化应激的影响,因为它们缺乏线粒体随后依赖G6PD和另一种戊糖磷酸途径酶产生NADPH。烟草烟雾中含有多种氧化剂并可能是一个有害的氧化应激的来源,在世界各地的人谁是G6PD缺乏。由于G6PD的至少一个常见变体与NADP的结合亲和力降低,因此,用烟酸或烟酰胺来提高细胞内NAD和NADP的浓度,可能会增强机体的还原能力并扭转这种缺陷的有害影响。虽然高浓度的烟酸增加了NAD的浓度和烟酰胺,NADP浓度似乎没有经过检查。

Defects in G6PD usually result in reduced enzymatic activity and a lower ratio of NADPH to NADP. Although some defects, including the Mediterranean polymorphism Ser188→Phe, do not affect cofactor binding (243), many G6PD defects, including at least one polymorphism, result in an increased Km for NADP and directly alter the NADP binding site. That polymorphism (G6PD Orissa, or Ala44→Gly) was found in a rural region in southern India and resulted in an enzyme with 15% activity and a 5-fold increased Km for NADP (59 compared with 12 mol/L) (244). Of 677 males screened in the Orissa region, 81 (12%) were G6PD deficient. Twenty-eight of the 81 G6PD-deficient men were fur-ther characterized, and 25 of them (89%) had an Ala44→Gly sub-stitution. This gives a polymorphic frequency of 11%.

G6PD中的缺陷通常导致酶活性降低和NADPH与Nadp的比例降低。虽然有一些缺陷,包括地中海多态Ser188→phe,但不影响辅因子结合。许多G6PD缺陷,包括至少一个多态性,导致一个NADP的KM增加和直接更改NADP绑定站点。这种多态性(G6PD Orissa,或Ala44→Gly)是在印度南部的一个农村地区发现的产生了一种活性为15%的酶和NADP的Km增加了5倍(59与12 mol/L相比),在Orissa地区筛查的677名男性中,81名(12%)G6PD缺陷。81例G6PD缺乏的男性中有28例具有皮毛特征,其中25例(89%)有Ala44→Gly取代。多态频率为11%。

A 514C→T missense mutation resulting in a Pro172→Ser amino acid substitution was found in a woman with chronic non-spherocytic hemolytic anemia (245). G6PD activity in this woman was 15% of normal in cultured skin fibroblasts, and the Km for NADP was raised nearly 4-fold (51 compared with 14 mol/L). When the mutant G6PD protein was expressed and purified from E. coli, activity was still decreased and Km increased. Another (rare) mutation, G6PD Santiago de Cuba Gly447→Arg, results in an enzyme with increased Km (43 compared with 3–5 mol/L) (243).

在一例慢性非球形溶血性贫血患者中发现了一个514 C→T错义突变,导致了Pro172Ser氨基酸的替换。在培养的皮肤成纤维细胞中,G6PD活性为正常人的15%。NADP的Km提高近4倍(51比14 mol/L)。当突变体G6PD蛋白从大肠杆菌中得到表达和纯化后,活性下降,Km增加。另一种罕见的突变,G6PJ447(古巴圣地亚哥)G4447a导致Km增加的酶(43,3~5 mol/L)(243)。

Many other residues have been implicated as residing in the NADP binding site because mutants either had an increased Km for NADP (G6PD Riverside Gly410→Cys) or could be (re)activated by high concentrations of NADP (G6PD Iowa Lys386→Glu), or both (G6PD Tomah Cys385→Arg, G6PD Bev-erly Hills Arg387→His, and G6PD Nashville Arg393→His) (246, 247). These results implicated residues 385–393 in the binding site. The structure of human G6PD, which was recently solved, confirms that these residues are likely responsible for cofactor binding (248). In particular, mutations at 389, 393, 394, and 398 reside near the structural NADP molecule. It seems clear that mutations at other sites could also alter protein conforma-tion so as to disrupt a cofactor binding site, which may explain their altered cofactor binding.

许多其他的残基被认为居住在NADP结合位点中,因为突变体对NADP的Km值要么增加了 (G6PD Riverside Gly410→Cys)或者被高浓度的NADP(G6PD,爱荷华Lys 386→Glu)激活,或(G6PD Tomah Cys 385→Arg,G6PD Bev-aryHills Arg 387→His,和G6PD Nashville Arg 393→His)。这些结果牵涉到残基385-393在装订地点。人类G6PD的结构,这件事最近被解决了,确认这些残基可能与辅因子结合有关。特别是389、393、394和398的突变位于NADP结构分子附近。显然,其他位点的突变也可能改变蛋白质的构象,从而破坏辅因子结合位点,这可能解释了它们改变的辅助因子结合。

Searches in the BLAST database (249) suggested that amino acids 29–210 are likely responsible for an NADP binding or recognition site and that this region is well conserved over a diverse set of organisms (data not shown). Two well-conserved residues (Ser188 and Ala44) that are affected by polymor-phisms—G6PD Mediterranean Ser188→Phe (one of the most common polymorphisms) and G6PD Orissa Ala44→Gly (which increases the Km for NADPH 5-fold)—fall into this putative NADP binding site.

在BLAST数据库中搜索,表明29-210氨基酸可能与NADP结合或识别位点有关而且这一区域在一组不同的有机体上是非常保守的(数据没有显示)。两个保守性很好的残基(Ser188和Ala 44),它们受到多相结构的影响-g6pd地中海Ser188→phe(最常见的多态性之一)而G6PD Orissa Ala44→Gly(使NADPH的Km增加5倍)-属于这个假定的NADP结合位点。

Mitochondrial transfer RNA leucine (UUR): MELAS syndrome 线粒体转移RNA亮氨酸(UUR):粒线体脑肌症候群

A tRNA mutation could result in a defective complex I via the incorporation of a critical leucine residue in complex I with low fidelity. Alternatively, because complex I depends on more mito-chondrial-encoded components than any other complex, it is possible that the nonspecific low-fidelity of leucine incorpora-tion would affect complex I more than the other complexes.

tRNA突变可通过在复合物I中引入关键亮氨酸残基而导致复合物I的缺陷,而复合物I的保真度较低。或者,因为复合物I比任何其他复合物都依赖更多的线粒体编码成分,亮氨酸结合物的非特异性低保真度对配合物I的影响可能大于其它配合物。

A MELAS patient with a mutation at nucleotide 3243 of the mitochondrial gene for tRNA leucine (UUR) (see OMIM 590050; also discussed in the section on riboflavin) was given nicotinamide therapy (1 g 4 times/d), which resulted in large reductions in blood lactate (40%) and pyruvate (50%) by day 3 of treatment (although the clinical effect of the treatment was temporary and the patient eventually died) (236). Blood NAD concentrations (a measure of intracellular erythrocyte concentration) were raised 24-fold by the sixth week of treatment, and it is speculated that the NAD increase with nicotinamide administration was probably universal because it occurred in a time- and dose-dependent man-ner in cultured fibroblasts from both the patient and the control subjects. The authors hypothesized that there was a complex I defect leading to an altered interaction between complex I and NADH that was responsible for the decreased complex I activity in the patient. The Km of complex I for NADH in skeletal muscle from the patient was similar to that in the control subjects; thus, nicotinamide supplementation was effective in this condition because of an enhancement of complex I activity with normal Km. In another case, a patient with the tRNA leucine (UUR) mutation at mitochondrial DNA base pair 3243 who initially presented with MELAS syndrome at the age of 19 y was clinically respon-sive to a mixture of riboflavin and nicotinamide, although the vitamins were not tested individually (220).

1例MELAS患者tRNA亮氨酸(UUR)线粒体基因3243核苷酸突变(UUR)(见OMIM 590050;也会在核黄素一节中讨论)烟酰胺治疗(1克4次/d),导致血乳酸大量减少(40%)和丙酮酸(50%)治疗的第3天(虽然治疗的临床效果是暂时的,病人最终死亡)。血NAD浓度(测定细胞内红细胞浓度)在治疗的第六周就提高了24倍,据推测,随着烟酰胺的使用,NAD的增加可能是普遍的,因为它发生在一段时间内-以及患者和对照组成纤维细胞的剂量依赖性。作者假设存在一个复杂的I缺陷,导致复合物I和NADH之间的相互作用改变,这是导致患者复杂I活性下降的原因。患者骨骼肌NADH复合物I的Km与对照组相似;因此,在这种情况下,添加烟酰胺是有效的,因为它增强了正常KM的复合物I的活性。在另一种情况下,一位患有tRNA亮氨酸的病人 (UUR) 线粒体dna碱基对3243突变最初在19岁时出现MELAS综合征,临床上对核黄素和烟酰胺混合物有反应,虽然没有单独测试维生素。

Dihydropteridine reductase: phenylketonuria II, hyperphenylalaninemia, and cognitive dysfunction
二氢蝶啶还原酶:苯丙酮尿症II,高苯丙氨酸血症,认知功能障碍

Dihydropteridine reductase (DHPR) utilizes the NAD-NADH redox system to catalyze the recycling of dihydrobiopterin to tetrahydrobiopterin. The tetrahydrobiopterin cofactor is used by the phenylalanine, tyrosine and tryptophan hydroxylases, which are necessary for dopamine and serotonin synthesis as well as nitric oxide synthase. Phenylalanine hydroxylase, when defec-tive, causes classic phenylketonuria (type I).

二氢喋啶还原酶 (DHPR)利用NAD-NADH氧化还原系统催化二氢生物蝶呤的再循环合成四氢生物蝶呤。四氢生物蝶呤辅因子被苯丙氨酸所使用,酪氨酸和色氨酸羟化酶,这对于多巴胺是必需的和5-羟色胺合成以及一氧化氮合酶。苯丙氨酸羟化酶,当失败时,会引起典型的苯丙酮尿症(I型).

The biochemical features of DHPR deficiency (see OMIM 261630), a disorder of biopterin metabolism resulting from defects in DHPR, involves hyperphenylalaninemia due to a block in the conversion of phenylalanine to tyrosine that is less severe than that of classic phenylketonuria. DHPR deficiency also involves deficient concentrations of various neurotransmitters in the central nervous system, causing severe neurologic symptoms. This is because of the reduced availability of tetrahydrobiopterin for tyrosine and tryptophan hydroxylases, as well as the compet-itive inhibition of these 2 hydroxylases by 7,8-dihydrobiopterin (N Blau, unpublished observations, 2001), which is the rearrange-ment product of normal dihydrobiopterin (6,7-dihydrobiopterin). Tetrahydrobiopterin deficiency may be an underappreciated cause of hyperphenylalaninemia and phenylketonuria; thus, it would be of interest to know how many children treated for phenylketonuria actually have the atypical form of the disease that is due to DHPR deficiency.

DHPR缺乏的生化特征(见OMIM 261630),由DHPR缺陷引起的生物蝶呤代谢紊乱,高苯丙氨酸血症是由于苯丙氨酸转化为酪氨酸的阻滞,比经典的苯丙酮尿症严重。DHPR缺乏还涉及中枢神经系统中各种神经递质的浓度不足,引起严重的神经症状。这是因为四氢生物蝶呤对酪氨酸和色氨酸羟化酶的可用性降低,以及7,8-二氢生物蝶呤对这2种羟化酶的竞争性抑制作用。这是正常二氢生物蝶呤(6,7-二氢生物蝶呤)的重排产物.四氢生物蝶呤缺乏可能是高苯丙氨酸血症和苯丙酮尿症的一个未被重视的原因;因此,有兴趣知道有多少治疗苯丙酮尿症的儿童实际上患有由DHPR缺乏症引起的非典型疾病。

More than 20 mutations in DHPR have been assigned to each of the 7 exons, with polymorphisms assigned to exons 3 and 4 (250). Two mutations in exon 1 could affect the ability of DHPR to bind the NAD cofactor: the first, Leu14→Pro, results in a noncon-servative substitution within the  βαβ structure (Rossmann fold) required for NADH binding and is suggested to result in an unstable protein subject to rapid degradation. Another mutation, Gly17→Val, resides in the highly conserved motif involved in NADH binding (251). At least one of these mutations results in no detectable immunoprecipitation and a severe phenotype. It is plausible that niacin administration could raise NADH concen-trations to stabilize these cofactor binding mutants or overcome Km defects caused by similar mutations.
在这7个外显子中,有20多个DHPR突变被分配给每个外显子,第3和第4外显子的多态性。外显子1的两个突变可能影响DHPR结合NAD辅助因子的能力:第一个,亮氨酸14-Pro、结果在βαβ结构中出现了一个非保守的替换(Rossmann fold) NADH结合所必需的,并被建议导致一种不稳定的蛋白质的快速降解。又一次突变,Gly 17→Val,位于NADH结合所涉及的高度保守的基序中。这些突变中至少有一个导致无法检测到的免疫沉淀和严重的表型。烟酸可以提高NADH浓度,稳定这些辅助因子结合突变体,或克服由类似突变引起的KM缺陷,这是合理的。

NADH directly increases the catalytic activity of DHPR in rat PC 12 cells (252), and it appears that activation of the defective enzyme via increased concentrations of NADH may serve as an additional benefit in humans. It is plausible that niacin-remediable defects in DHPR occur in humans and that they are the result of a decreased affinity for NADH.

NADH直接提高DHPR在大鼠PC 12细胞中的催化活性,而且看来,通过增加NADH浓度来激活有缺陷的酶,可能对人类有额外的好处。这是合理的,烟酸补救的缺陷在人类发生DHPR和他们的结果是降低了对NADH的亲和力。

Treatment of phenylalanine hydroxylase deficiency with tetra-hydrobiopterin, which bypasses the DHPR reaction, has been successful (253), which affirms that proper tetrahydrobiopterin availability is essential for this pathway. However, tetrahydro-biopterin therapy is not useful in DHPR deficiency because DHPR is involved in the recycling, and not biosynthesis, of tetrahydro-biopterin. Thus, bypassing the DHPR reaction with tetrahydrobio-pterin therapy would require equimolar amounts of phenylalanine. On the other hand, increasing intracellular NADH concentrations would hypothetically increase the tetrahydrobiopterin recycling activity of DHPR and this could alleviate the reduced availability of tetrahydrobiopterin.

四氢生物蝶呤治疗苯丙氨酸羟化酶缺乏症,它绕过了dhpr反应,已经取得了成功。这肯定了正确的四氢生物蝶呤的有效性是必不可少的这一途径。然而,四氢生物蝶呤治疗DHPR缺乏并不有效,因为DHPR参与了回收,而不是生物合成,四氢生物蝶呤。因此,绕过DHPR反应与四氢生物翼蛋白治疗将需要等摩尔量的苯丙氨酸。在另一方面,增加细胞内NADH浓度,假设会提高DHPR的四氢生物蝶呤循环活性这可以减轻四氢生物蝶呤的可利用性。

In a study of 88 infants treated for phenylketonuria, between 48% and 80% of subjects had intakes of preformed niacin, but not a variety of other vitamins, below two-thirds of the 1968 rec-ommended dietary allowance (254).

在一项对88名治疗苯丙酮尿症婴儿的研究中,48%到80%的受试者服用过预先形成的烟酸,但不包括其他维生素,低于1968年推荐摄入量的三分之二。

Long-chain-3-hydroxyacyl-CoA dehydrogenase  subunit: hypoglycemia, cardiomyopathy, and sudden death
长链羟酰基辅酶A脱氢酶亚组:低血糖、心肌病和猝死
The mitochondrial trifunctional protein, composed of 4 αand 4 β subunits, is responsible for the last 3 steps of the β-oxidation of long-chain fatty acids, which is the main source of energy in the heart. The subunit contains the long-chain-3-hydroxyacyl-CoA dehydrogenase (LCHAD), which catalyzes the following NAD-dependent reaction: R-CHOH-CH2-CO-S-CoA + NAD → R-CO-CH2-CO-S-CoA + NADH + H+.

线粒体三功能蛋白,由4个α和4个β亚基组成,负责β氧化长链脂肪酸的最后三个步骤,这是心脏的主要能量来源。该亚基含有长链-3-羟基酰基-辅酶A脱氢酶(LCHAD),催化以下NAD依赖反应:R-CHOH-CH2-CO-S-CoA + NAD → R-CO-CH2-CO-S-CoA + NADH + H+.

Mitochondrial trifunctional protein deficiency resulting from impaired LCHAD activity (see OMIM 600890) is the second most common inborn error of fatty acid metabolism, second onlyto MCAD deficiency (discussed in the section on riboflavin). Clinical complications include hypoglycemia, cardiomyopathy, and sudden death. In addition, severe maternal illness (eg, acute fatty liver) during pregnancy often accompanies mitochondrial trifunctional protein deficiency in the fetus (255).

LCHAD活性受损所致线粒体三功能蛋白缺乏症(见OMIM 600890)是脂肪酸代谢的第二大先天错误,二是MCAD缺陷(在核黄素一节中讨论)。临床并发症包括低血糖、心肌病和猝死。此外,严重的产妇疾病(如急性脂肪肝),妊娠期常伴有胎儿线粒体三功能蛋白缺乏。

The DNA mutation 1528G→C in the subunit, resulting in an Glu510→Gln substitution (Glu474→Gln in some papers), was found to be directly responsible for the loss of LCHAD activity and subsequent illness, although it does not seem to affect over-all conformation or subunit conformation because no difference in molecular weight was found between wild-type and mutant proteins. The allele frequency of G1528 was found to be 87% in 34 LCHAD-deficient patients, and there is speculation that the 1528G→C mutation affects the active site of the dehydrogenase domain of mitochondrial trifunctional protein (256).

基因突变1528 G→C在亚基中,导致Glu510→Gln替换(Glu474→Gln在一些论文中),被认定对LCHAD活动的损失负有直接责任和随后的疾病,虽然它似乎没有影响所有的构象或亚单位构象,因为在分子量没有发现野生型和突变型蛋白质。G 1528等位基因频率在34例LCHAD缺陷患者中为87%,推测1528 G→C突变影响线粒体三功能蛋白脱氢酶结构域的活性位点。

We have assigned the Glu510→Gln mutation to the likely NAD binding domain (amino acids 358–542) by querying the Con-served Domain Database of the National Center for Biotechnology Information (257) with the LCHAD subunit protein sequence. These results were verified by aligning the protein sequence of LCHAD with that of the short-chain enzyme, SCHAD [the first 200 amino acids of which are responsible for NAD binding (258)], by using the Pairwise BLAST tool (249). Amino acids 27–314 of SCHAD lined up with amino acids 361–640 of LCHAD with 33% identity, 52% similarity, and 3% gaps. Residue Glu510 is con-served in the 2 enzymes. Although it appears that kinetic studies have not been performed on LCHAD, it would be of interest to study the NAD binding affinity of the mutant enzyme and to test the responsiveness of LCHAD-deficient patients to therapy with nicotinic acid or nicotinamide, pre- or postnatal.

我们已将Glu510→Gln突变分配给可能的NAD结合域(氨基酸358-542)通过查询国家生物技术信息中心Con-service域数据库LCHAD亚基蛋白序列。通过对LCHAD蛋白序列与短链酶序列的比对,验证了上述结果的正确性。Schad[其前200个氨基酸负责NAD结合,使用成对的爆破工具。SCHAD的27~314氨基酸与LCHAD的361~640氨基酸排列一致,同源性为33%,相似性52%,间隙3%。谷胱甘肽510在这2种酶中起主要作用。虽然似乎没有对LCHAD进行动力学研究,因此,研究突变酶的NAD结合亲和力是很有意义的并检测LCHAD缺乏症患者出生前后对烟酸或烟酰胺治疗的反应性。

Hyperlipidemia and heart disease 高脂血症与心脏病

Patients with hyperlipidemia, an inheritable set of disorders 高脂血症患者,一组可遗传的疾病
involving altered lipid metabolism, were studied for response to colestipol, lovastatin, simvastatin, niacin, and placebo (259). (Statins are inhibitors of the cholesterol biosynthetic enzyme, 3-hydroxy-3-methylglutaryl CoA reductase.) Although niacin was not tested alone (but rather in conjunction with colestipol or simvastatin), it appears to have improved HDL, triacylglycerol, and cholesterol concentrations in patients.

涉及脂质代谢的改变,研究了对Colestipol的反应,洛弗斯塔特因(用于降低血液中的胆固醇),HMG辅酶A还原酶抑制剂,烟酸,和安慰剂(他汀类药物是胆固醇生物合成酶3-羟基-3-甲基戊二酰辅酶A还原酶的抑制剂。)虽然烟酸不是单独测试的(而是与克拉斯波尔或辛伐他汀联合使用),它似乎改善了HDL,三酰甘油和胆固醇在病人中的浓度。

Combined niacin and statin use has been recommended because of success in clinical trials for the reduction in cardio-vascular events and improvement in progression or regression of coronary lesions (260). The niacin-statin treatment regimen appears to provide a unique combination of marked LDL-cholesterol reduction along with favorable changes in HDL cho-lesterol, lipoprotein(a), and triacylglycerol. A review of the use of niacin to prevent cardiovascular disease and related complica-tions gives evidence of multiple trials of successful treatment with niacin, including the Coronary Drug Project, the largest of the trials studied, which concluded that niacin monotherapy leads to significant decreases in recurrent myocardial infarctions and cerebrovascular events (261).

联合烟酸和他丁类推荐使用是因为在减少心血管事件的临床试验中取得了成功冠状动脉病变进展或消退的改善。烟酸-他汀治疗方案似乎提供了显著的低密度脂蛋白胆固醇降低和高密度脂蛋白胆固醇的良好变化的独特组合,脂蛋白(A),还有三酰甘油。对烟酸预防心血管疾病及相关并发症的应用进行综述,提供了烟酸治疗成功的多项试验证据,包括冠状动脉药物项目,研究中最大的一项试验得出结论,烟酸单药治疗可显著减少反复发作的心肌梗死和脑血管事件。

The benefits of niacin treatment in the lowering of LDL cho-lesterol was tested in a randomized, controlled, double-blind study involving 201 men and women with elevated LDL-cholesterol values (in the 75th to 95th percentiles) (262). Four treatment groups (receiving daily niacin doses of 2000, 1500, 1250, and 1000 mg) were compared with placebo and diet-treated control groups. The groups given 2000 and 1500 mg had significant reductions in LDL cholesterol (26% and 19.3%, respectively),total cholesterol (18.4% and 13.3%), and the ratio of total to HDL cholesterol (20.4% and.4%) when compared with the placebo and diet-treated control groups. Smaller improvements were seen in HDL-cholesterol and triacylglycerol concentrations. Blood chem-istry monitoring indicated that a reduction in LDL-cholesterol concentration strongly correlated with an increase in baseline concentrations of some enzymes for niacin-treated subjects.

烟酸治疗降低密度脂蛋白胆固醇的益处在一项随机的、对照的双盲研究中进行了试验,该研究涉及201名具有较高低密度脂蛋白胆固醇值的男性和女性(第75至95百分位数)。四个治疗组(每日烟酸剂量分别为2000、1500、1250和1000毫克)与安慰剂进行比较和饮食治疗对照组。2000和1500毫克组的低密度脂蛋白胆固醇显著降低(分别为26%及19.3%),,总胆固醇(18.4%和13.3%),总胆固醇与高密度脂蛋白胆固醇的比率(20.4%和4%)与安慰剂相比和饮食治疗对照组。HDL-胆固醇和三酰甘油浓度的改善较小.血液化学监测显示,低密度脂蛋白胆固醇浓度的降低与烟酸治疗组某些酶基线浓度的增加密切相关。

Schizophrenia 精神分裂症

“It is supposed that the favorable therapeutic effects of nico-tinamide, nicotinic acid and their active biological form—NAD—are realized due to the mechanisms of their functioning in the ner-vous system, for treating schizophrenia, epilepsy and other diseases of the nervous system” (263). Hoffer (264) and Pauling (265) review literature pertaining to the use of various forms of niacin to treat schizophrenia. They found several studies in which success was reported with niacin therapy. However, these conclusions have been criticized (266) for failure of the investi-gators to support their claims with evidence from double-blind and placebo-controlled studies, which are necessary to ascertain the efficacy of vitamin treatment of schizophrenia. See also the discussion of MTHFR in the section on folic acid.

“人们认为尼可丁酰胺有良好的治疗作用,烟酸及其活性生物形态-NAD-由于其在NE-VOU系统中的作用机制而得以实现,治疗精神分裂症,癫痫和其他神经系统疾病,霍夫和鲍林回顾有关使用各种形式烟酸治疗精神分裂症的文献。他们发现了几项关于烟酸治疗成功的研究。然而,这些结论受到了批评投资者未能用双盲证据来支持他们的主张和安慰剂对照研究,这对于确定维生素治疗精神分裂症的疗效是必要的。另见关于叶酸一节中对MTHFR的讨论。

Chronic fatigue syndrome 慢性疲乏综合征
Eight of 26 patients (31%) with chronic fatigue syndrome responded favorably to NADH treatment as opposed to only 2 of 26 control subjects (8%) (267). Although NADH therapy appears to be helpful in some patients, the cause of this syndrome is unknown and clinical assessment is sometimes difficult.

26例慢性疲劳综合征患者中8例(31%)对NADH治疗反应良好,而26名对照组中只有2名(8%)。虽然NADH治疗在某些患者中似乎是有帮助的,但其病因不明,有时难以进行临床评估。

Necrobiosis lipoidica 类脂质渐进性坏死
Nicotinamide treatment improved 8 of 13 patients with this granulomatous condition, which involves abnormalities in der-mal collagen, vascular supply of the skin, and immunologic responses (268).

烟酰胺治疗改善了13例肉芽肿患者中的8例,其中包括正常胶原蛋白的异常,皮肤血管供应与免疫反应。

Dihydrolipoamide dehydrogenase: lactic acidosis See the discussion in the section on lipoic acid.
二氢硫辛酰胺脱氢酶; 乳酸酸中毒见关于硫辛酸一节的讨论。

Methionine synthase reductase: homocystinuria and mental retardation 蛋氨酸合成酶还原酶:高胱氨酸尿和智力迟钝

See the discussion in the section on cobalamin. 见关于钴胺一节的讨论

Tissue concentrations and toxicity 组织浓度和毒性

The DRI manual enumerates various adverse effects of sup-plemental niacin use, but these effects are usually associated with doses of nicotinic acid of ≥ 1500 mg/d (7). It appears that nicotinamide produces fewer side effects than nicotinic acid. This difference could be due to study bias, however, if signifi-cantly fewer studies with nicotinamide have been performed.

DRI手册列举了服用硝酸氢钠的各种不良反应,但这些作用通常与≥1500 mg/d的烟酸剂量有关。看来烟酰胺产生的副作用比烟酸少,这种差异可能是由于研究偏见,然而,如果显着地减少了对烟酰胺的研究。

Niacin administration raises NAD concentrations in rodents. In mice, the relation of niacin concentration in the diet to NAD in skin fits a logarithmic function, suggesting that NAD content approaches saturation at 0.5–1.0% niacin (g niacin/kg diet) supplementation (269). In rats, 2 wk of dietary nicotinic acid supplementation (500 and 1000 mg/kg diet) caused elevated con-centrations of NAD in the blood, liver, heart, and kidney, whereas nicotinamide caused elevated concentrations only in the blood and liver, compared with controls fed a diet containing 30 mg nicotinic acid/kg. Both nicotinic acid and nicotinamide, at 1000 mg/kg diet, cause elevations in liver NAD, by 44% and 43%,respectively (270). As mentioned above, nicotinamide has been shown to increase human intracellular NAD concentrations (236). Doses of nicotinic acid of 100 mg/d raise human lymphocyte NAD concentrations 5 times above baseline (235). At higher concentrations, passive diffusion predominates, with doses of 3–4 g niacin almost completely absorbed (271).

烟酸可提高啮齿动物体内NAD浓度。在小鼠中,饮食中烟酸浓度与皮肤NAD的关系符合对数函数,表明NAD含量在0.5%~1.0%烟酸增补剂时接近饱和 (g niacin/kg diet)。大鼠日粮中添加烟酸(500 mg/kg和1000 mg/kg)2wk可引起大鼠血液中NAD浓度升高,肝脏、心脏和肾脏,而烟酰胺只引起血液和肝脏中的浓度升高,与对照组相比,添加30毫克烟酸/千克。烟酸和烟酰胺,1000毫克/千克的饮食,引起肝脏NAD升高,分别为44%和43%。如上文所述,烟酰胺可增加人细胞内NAD的浓度。剂量为100 mg/d的烟酸使人淋巴细胞NAD浓度比基线高出5倍。高浓度时,以被动扩散为主,3-4 g烟酸几乎完全吸收。

BIOTIN (VITAMIN B-7) 生物素(维生素B-7)

The DRI for biotin is 30 μg/d (7).生物素的相对分子质量比为30μg/d
Holocarboxylase synthetase: multiple carboxylase deficiency, organic aciduria, seizures, and ataxia Holocarboxylase synthetase (HCS), or biotin–[propionyl-CoA-carboxylase (ATP-hydrolysing)] ligase (Table 7), catalyzes 1) the formation of biotinyl-AMP from biotin and ATP, and 2) the transfer of biotin from biotinyl-AMP to enzymatically inactive apocarboxylases to form active holocarboxylases (272). Specifically, HCS catalyzes the biotinylation of the 4 biotin-dependent carboxylases found in humans: the mitochondrial propionyl-CoA carboxylase, pyruvate carboxylase, -methylcrotonyl-CoA car-boxylase, and the cytosolic acetyl-CoA carboxylase.

全羧化酶合成酶:多羧化酶缺乏症、有机酸尿、癫痫发作和共济失调全羧化酶合成酶(HCS),或生物素-[丙酰辅酶-羧化酶(ATP-水解)]连接酶,催化1)生物素和ATP合成生物素-AMP和(2)生物素从生物素酰-AMP转移到酶活性不活跃的脱辅基羧化酶形成活性全羧酶。具体来说,HCS催化4种依赖于生物素的羧化酶的生物素化:线粒体丙酰基-CoA羧化酶,丙酮酸羧化酶,-甲基巴豆酰-CoA汽车-羧化酶,以及胞浆乙酰辅酶A羧化酶。

Multiple carboxylase deficiency due to HCS deficiency (see OMIM 253270) presents in children anywhere from the time of birth to 15 mo of age. Symptoms include organic aciduria, feed-ing difficulties, neurologic abnormalities (subependymal cysts, hypotonia, impaired consciousness, seizures, and ataxia), and cutaneous changes (rash and alopecia). Supplemental biotin (10 mg/d, compared with an DRI of 30 μg/d) can commonly pro-vide sufficient substrate to increase HCS enzymatic function (when the Km is increased and the Vmax is decreased) and thereby permit biotinylation of the 4 carboxylases (273).

HCS缺乏症致多发性羧化酶缺乏症(见OMIM 253270)从出生到15岁的任何地方的儿童礼物。症状包括有机酸尿,喂养困难,神经异常(室管膜下囊肿、低张力、意识受损、癫痫和共济失调),和皮肤改变(皮疹和脱发)。补充生物素(10 mg/d,而dRI为30μg/d)通常能提供足够的底物来增加hcs的酶功能(当Km增加,Vmax降低时),从而允许4种羧化酶的生物素化。

Cowan et al (274) reported the first biotin-responsive patient, who displayed acidurias reflecting deficiencies in multiple car-boxylase enzymes. Oral biotin treatment (10 mg/d) significantly decreased urine acid concentrations. The same group was the first to diagnose and treat an HCS deficiency case prenatally (275). An elevated Km (> 100 times) of HCS for biotin as well as a depressed Vmax were found in fibroblasts from the child.
Cowan等人,报告了第一位对生物素有反应的病人,他表现出酸尿症,反映了多种羧化酶的缺陷。口服生物素(10 mg/d)可显著降低尿酸浓度。同一组是第一个诊断和治疗hcs缺乏症的人。在儿童成纤维细胞中发现,生物素的Km(>100倍)升高,Vmax降低。

Two other patients with HCS deficiency had Km values 14 and 28 times greater than normal at 7.2 and 3.7 μmol/L (compared with the control value of 0.260 μmol/L) (n = 5). The Vmax of the enzyme from the patients was also significantly lower than that of the control subjects (276).

另外两例HCS缺乏症患者在7.2和3.7μ/L时的Km值分别是正常人的14倍和28倍(与对照值0.260μ/L相比)(n=5)。患者的Vmax也明显低于对照组。

Analysis was performed on a mutant, Val550→Met, which resides in the putative biotin binding site (277). In fibroblasts transfected with the Val550→Met cDNA, the Km for biotin (0.943 mol/L) was larger than the value found for the wild-type cDNA (0.145 mol/L). Additionally, the Vmax decreased to 10 pmol · min-1 · mg-1 in the mutant compared with a wild-type Vmax of 60 pmol · min-1 · mg-1.

对一个突变体Val550→Met进行了分析,该突变体位于假定的生物素结合位点上。转染Val550→MetcDNA的成纤维细胞中,生物素的Km(0.943 mol/L)大于野生型的Km(0.145 mol/L)。突变体Vmax降至10 pmol·min-1·mg-1,野生型Vmax为60 pmol·min-1·mg-1。

Of 6 different point mutations analyzed in the HCS gene, 2 are frequent among patients with multiple carboxylase deficiency: Val550→Met and Arg508→Trp (which appears to be spread worldwide across ethnic groups). Dupuis et al (278) reported that “four of the mutations cluster in the putative biotin-binding domain as deduced from the corresponding E. coli enzyme and consistent with an explanation for biotin-responsiveness based on altered affinity for biotin. The two others may define an additional domain involved in biotin-binding or biotin-mediated sta-bilization of the protein.”

在HCS基因分析的6个不同的点突变中,多发性羧化酶缺乏症患者中2例多见:Val550→Met和Arg 508→Trp(这似乎遍及世界各地的种族群体)。Dupuis等人(278)报告说,“从相应的大肠杆菌酶中推断出的生物素结合区的四个突变簇,与生物素反应的解释是一致的-基于生物素亲和力的改变。另外两个可能定义了另一个与生物素结合或生物素介导的蛋白质合成有关的结构域。“

Dupuis et al (278) characterized the Arg508→Trp mutation, found in 4 (3 heterozygous, 1 homozygous) of 9 multiple car-boxylase deficiency patients screened, as residing in the biotin binding site. “We anticipate that the four mutations in the biotin-binding region of HCS will account for the high Km for biotin measured in patients with neonatal MCD. For example, two of the patient fibroblast lines we studied, JRi and MC, had a reported Km of 0.346 and 0.048 mol/L, respectively, compared with 0.015 mol/L for the normal enzyme. JRi was found to have an [Arg508→Trp] mutation and MC was found to have a [Val550→Met] mutation (in each case, the second mutation has yet to be identified). While it is premature to conclude that these mutations are causative of the elevated Km, their location in the biotin-binding region and the conservation of three of the four mutations among human, Paracoccus denitrificans, E. coli, Bacil-lus subtilis, Salmonella typhimurium, mouse and yeast biotin lig-ases is consistent with this notion” (278).

Duet等人,对9例多重羧化酶缺乏症患者中4例(3例杂合子,1例纯合子)的arg 508→Trp突变进行了鉴定,发现该突变位于生物素结合位点。“我们预计,HCS生物素结合区的四个突变将解释在新生儿MCD患者中生物素含量高的KM值,例如,我们研究的两种患者成纤维细胞系JRI和MC的Km分别为0.346和0.048 mol/L,正常酶分别为0.015 mol/L和0.015 mol/L。JRI被发现有一个[arg 508→trp]突变,mc被发现有一个[val550→meet]突变(在每种情况下,第二个突变都有y)。et to be identified).虽然认为这些突变是KM升高的原因还为时过早,它们在生物素结合区的位置以及人类四种突变中三种的保守性,假单胞菌、大肠杆菌、枯草芽孢杆菌、伤寒沙门氏菌、小鼠和酵母生物素酶均符合这一概念。

Of 7 HCS mutations analyzed, 2 (Gly581→Ser and delThr610) were found to reside in the putative biotin binding region of HCS and resulted in increased Km values by 45-fold and 3-fold, respectively. The other 5 mutations were outside the biotin binding region. Administering biotin to Gly581→Ser mutant cells in culture increased propionyl-CoA carboxylase activity to control levels, whereas such treatment did not affect other mutant lines that had mutations outside the putative biotin binding domain (279).
分析7个hcs突变中,2例(Gly 581→Ser和delThr 610)被发现存在于hcs的生物素结合区使Km值分别提高45倍和3倍.其余5个突变位于生物素结合区以外。将生物素应用于Gly 581→Ser突变细胞培养,可提高丙酰基辅酶A羧化酶活性,达到对照水平,然而,这种处理并不影响其他突变系,这些突变系在假定的生物素结合域之外有突变。

By prenatal diagnosis, a 33-fold elevated Km for biotin was found in a fetus (Km patient, 0.221 μmol/L; control subject, 0.007 μmol/L). The mother was given 10 mg biotin/d and the newborn, who was clinically well, was maintained on biotin treatment after birth at 20 mg/d (280).

通过产前诊断,在胎儿体内发现了33倍高的生物素(KM患者,0.221μ/L,对照组,0.007μ/L)。母亲每天服用10毫克生物素,新生儿出生后继续接受20毫克/天的生物素治疗,临床表现良好。

The Km measured from amniocytes of a woman pregnant with another HCS-deficient child diagnosed prenatally was 12 times greater than control, and Vmax was 2% of control (281). Biotin responsiveness was shown in vitro, with the restoration of car-boxylase activities to 51–58% of normal. The infant’s Km was increased as well to 0.060 μmol/L (control: 0.007 μmol/L). The mother was treated prenatally and the infant was clinically well at birth.

从另一位患有hcs缺陷的孕妇的羊膜细胞中检测出的Km值是对照组的12倍,Vmax为对照组的2%。生物素活性在体外表现为正常人的51-58%。婴儿的Km也增加到0.060μ/L(对照组:0.007μ/L)。母亲接受了产前治疗,婴儿出生时临床表现良好。

Five biotin-responsive patients with a defect in holocarboxylase synthesis were reported by Suormala et al (282). Enzyme activities and Km were measured and clear evidence was presented that many HCS cases respond to biotin because of a Km defect in the enzyme. In 3 patients, normalization of biochemical indexes required doses of 20–40 mg/d. The fourth patient required a dose of 100 mg biotin/d before her skin rash disappeared, but she remained mentally retarded and showed slightly elevated urinary organic acid excretion. The results in the 5 patients suggest a pri-mary defect in HCS resulting from a decreased affinity for biotin, in one patient combined with a decreased Vmax.

Suormala等人报告了5例生物素应答患者的全羧化酶合成缺陷。对酶活性和Km进行了测定,并有明确的证据表明,许多HCS病例是由于生物素存在Km缺陷而对生物素产生反应的。3例患者生化指标正常化需剂量20~40 mg/d。第四位病人在皮疹消失之前需要服用100毫克生物素/天,但她仍然智力迟钝,尿有机酸排泄略有增加。5例患者的结果提示HCS存在PRI-Mary缺陷,这是由于与生物素的亲和力降低所致,1例合并Vmax降低。

A new polymorphism, 1121C→T, was identified in the mutational analysis of 7 patients with HCS deficiency (283). Note also that there are many known mutations in HCS that do not affect the biotin binding site; thus, an altered Km would not explain those cases.

一种新的多态性,1121C→T,对7例HCS缺乏症患者进行突变分析。还要注意的是,HCS中有许多已知的突变不影响生物素结合位点;因此,改变的KM不能解释这些情况。

Tissue concentrations and toxicity 组织浓度和毒性

There seems to be good evidence that pharmacologic doses of biotin increase biotin concentrations in tissues and plasma (284). Normal plasma and whole-blood biotin concentrations are 2 nmol/L (277). The serum biotin concentration of one patient taking 20 mg biotin/d was raised to 4.8 μmol/L, which was 4.5 times greater than the Km for biotin of his HCS enzyme (285). More generally, 10 mg oral biotin daily is believed to produce concentrations of biotin in plasma of 1.3 mol/L, well above the Km for biotin of HCS of most patients with HCS deficiency (285). Lower dosages (≥ 600 μg/d) used in another study raised plasma biotin concentrations 7-fold (from 0.3 to 2.8 nmol/L), whereas concentrations of the “quantitatively most important biotin metabolite, bisnorbiotin,” were raised 15.5 times in plasma post-supplementation (286).

似乎有很好的证据表明生物素的药理学剂量增加了组织和血浆中生物素的浓度。正常血浆和全血生物素浓度为2 nmol/L。1例服用20 mg生物素/d者,血清生物素浓度提高至4.8mol/L,比HCS酶中生物素的Km值高4.5倍。更普遍的是,每天10毫克的口服生物素被认为能在血浆中产生浓度为1.3 mol/L的生物素,大多数HCS缺乏症患者HCS生物素水平高于Km值。在另一项研究中,低剂量(≥600μg/d)可使血浆生物素浓度提高7倍(从0.3nmol/L提高到2.8nmol/L),然而,“定量最重要的生物素代谢物,双去甲生物素”在血浆补充后的浓度提高了15.5倍。

No UL for biotin has been set. Toxicity has not been reported in patients receiving daily doses of ≤ 200 mg orally and ≤ 20 mg intravenously for the treatment of biotin-responsive inborn errors of metabolism and acquired biotin deficiency (7).

未建立生物素UL。每日口服≤200毫克及静脉注射≤20毫克以治疗生物素反应的先天代谢错误及后天生物素的患者,并无毒性报告。

COBALAMIN (VITAMIN B-12) 钴胺(维生素B-12)

The DRI for vitamin B-12 is 2.4 μg/d for adults (7). Cobalamin is the precursor to methylcobalamin and adenosylcobalamin, the bioactive cofactor forms of cobalamin. Cobalamin-dependent enzymes are listed in Table 8.

维生素B-12的DRI为2.4μg/d。钴胺是甲钴胺和腺苷钴胺的前体,腺苷钴胺是钴胺的生物活性辅助因子。钴胺依赖酶列于表8.

Methylmalonyl-CoA mutase: methylmalonic aciduria and cognitive dysfunction

甲基丙二酰-辅酶A变位酶:甲基丙二酸尿与认知功能障碍

Methylmalonyl-CoA mutase is a mitochondrial enzyme that requires adenosylcobalamin to catalyze the isomerization of methylmalonyl-CoA to succinyl-CoA. Deficiency of methyl-malonyl-CoA mutase leads to methylmalonic aciduria (see OMIM 251000). Symptoms include multiple episodes of life-threatening organic acidosis and hyperammonemia associated with low-normal intelligence in the first years of life. Patients often respond to pharmacologic supplements of cobalamin (cyanoco-balamin or hydroxycobalamin) leading to a reduction in methyl-malonate accumulation. It is possible that from one-third to one-half of mutations in methylmalonyl-CoA mutase confer a reduced ability to bind cobalamin cofactor. A newborn screening program identified 17 children with methylmalonic aciduria, of whom 7 (41%) were cobalamin responsive (287).

甲基丙二酰辅酶是一种线粒体酶这就需要腺苷钴胺催化甲基丙二酰-辅酶A异构化为琥珀酰辅酶A。甲基丙二酰辅酶缺乏导致甲基丙二酸尿(见OMIM 251000)。症状包括多起危及生命的有机酸中毒和高氨血症相关的低正常智力在生命的头几年。病人经常对钴胺(氰基巴拉明或羟基钴胺)的药理学补充剂产生反应,从而减少了丙二酸甲酯的积累。甲基丙二酰辅酶变异的三分之一到一半可能降低了钴胺辅助因子的结合能力。一项新生儿筛查发现17名患有甲基丙二酸尿的儿童,其中7名(41%)对钴胺有反应。

Enzymes from fibroblasts of 4 remediable patients had ele-vated Km values for adenosylcobalamin, suggesting a perturbation in cofactor binding (3). The nonremediable genetic defects con-stitute about two-thirds of those found and the remediable defects about one-third (3). The latter defective proteins retain some enzyme activity (2–75% of control) and have an increased Km for adenosylcobalamin of 200–5000 times normal (288–290).

4例可治愈患者成纤维细胞的酶对腺苷钴胺的Km值进行了测定,暗示辅因子结合的扰动。这些无法弥补的基因缺陷约占被发现基因缺陷的三分之二还有约三分之一的可弥补的缺陷。还有约三分之一的可弥补的缺陷而腺苷钴胺的Km值是正常值的200-5000倍。

Kinetic analysis of one cobalamin-responsive patient showed abnormal binding of the coenzyme, adenosylcobalamin, for its methylmalonyl-CoA mutase apoenzyme, ie, a Km of 38 mmol/L compared with the control Km of 0.015 mmol/L. A decreased Vmax (14% of control) was found as well. It was concluded that the defect was “at the [adenosylcobalamin]-binding site since the Km for the substrate, [methylmalonyl-CoA], is similar to con-trols whereas the Km for [adenosylcobalamin] binding differs by 2,600-fold” (290).

一例钴胺反应患者的动力学分析显示辅酶腺苷钴胺异常结合,甲基丙二酰辅酶A酶的Km为38 mmol/L,与对照KM的0.015 mmol/L相比,A的Vmax降低了14%。我们的结论是,缺陷是“在[腺苷钴胺]结合位点,因为KM为底物,[甲基丙二酰辅酶A]与对照组相似,而[腺苷钴胺]结合的Km值相差2,600倍“。

In an examination of the fibroblasts from 2 other patients with a cobalamin-remediable phenotype, a decreased affinity of the mutant enzyme for adenosylcobalamin was found. The Km values of the mutant enzymes for adenosylcobalamin were 280 and 17 mmol/L, compared with control Km values of 0.06–0.07 mol/L (an 2000-fold increase in Km). The Vmax of both enzymes was decreased to 20% and 5% of control (288).
在对其他2例钴胺可修复表型的成纤维细胞的检查中,突变酶对腺苷钴胺的亲和力降低。腺苷钴胺突变酶的Km值分别为280和17 mmol/L。与对照相比,Km值为0.06-0.07mol/L(公里数增加2000倍)。两种酶的Vmax分别为对照的20%和5%。

Two types of mutations have been described, those leading to no detectable activity (mut0), which are not corrected by excess cobalamin, and those exhibiting residual activity (mut), which are corrected by excess cobalamin. X-ray structure analy-ses showed many of the latter mutations to be in the cobalamin binding site of the enzyme (291). This observation is consis-tent with a Km mutation as an explanation for the cobalamin-dependent phenotype.

已经描述了两种突变,导致无法察觉的活动(mut0),它没有被过量的钴胺所纠正,和那些表现出残余活度的人(Mut),由过量的钴胺纠正。X射线结构分析显示,后一种突变存在于酶的钴胺结合位点。这是一个Km突变解释钴胺依赖表型的结论。

Altered enzymes without detectable residual mutase activity (< 0.1%) were found in those patients not responsive to cobalamin (289). None of 7 mut0 mutant lines examined had any detectable mutase activity, even when assayed in 1 mmol adenosylcobalamin/L (a value >10000 times the control Km for adenosylcobalamin). The 7 mutant lines with mut activity (0.5–50% of control) showed an increased activity in cell extracts with hydroxycobalamin supplementation. These latter altered enzymes had a 50- to 5000-fold elevated Km for adenosyl-cobalamin and one mutase examined turned over at a rate 3–4 times higher than that of the control enzyme when the cells were grown in hydroxycobalamin-supplemented medium. Six, and possibly all 7, of these had an elevated Km for adenosylcobalamin ranging from 2 to 290 mol/L (control Km: 0.04–0.08 mol/L). The Vmax was also decreased: 7–725 pmol·min1 ·mg1 com-pared with control values of 1053–1827 pmol·min1 ·mg1. Five of 8 mutase heterozygotes examined expressed some mutase activity with reduced affinity for cofactor (289).

未检测到残余变位酶活性的改变酶 (< 0.1%) 在那些对钴胺没有反应的病人身上发现。检测到的7个变异系中没有一个具有任何可检测到的变位酶活性,即使在1 mmol腺苷钴胺/L中测定 (a值>10000倍于对照公里的腺苷钴胺)。7个具有mut活性的突变系(占控制的0.5%-50%)添加羟钴胺可提高细胞提取物的活性。后一种改变的酶对亚丁酰钴胺有50到5000倍高的km和其中一个变位酶的翻转率要高出3-4倍当细胞在添加羟钴胺的培养基中生长时,比对照酶的作用更明显。其中6种,可能全部7种,腺苷钴胺的Km升高范围从2到290 mol不等。/L(对照Km:0.04-0.08mol/L)。Vmax也降低:7~725 pmol·min1·mg1com,与对照值1053~1827 pmol·min1·mg1相比,差异有显着性(P<0.01)。8种变位酶杂合子中有5种表达了一定的变位酶活性。余因子的有限性

In another study of cell lines from patients with methyl-malonic aciduria, 3 of 4 exhibited cobalamin-responsiveness. The Gly717→Val mutant enzyme was expressed in cell culture and was found to have a 1000-fold higher Km for adenosylcobal-amin and an increase in activity in response to high concentra-tions of cobalamin. Four novel mutations described are near the carboxyl end of the protein and are hypothesized to reside in the adenosylcobalamin binding site (292, 293).

在另一项对甲基丙二酸尿患者细胞株的研究中,4例中有3例表现出钴胺反应.Gly 717→val突变酶在细胞培养中表达,并被发现其对腺苷酰辅酶的Km值是对照酶的1000倍以及高钴胺浓度引起的活性增加。所描述的四个新的突变位于蛋白的羧基端附近,并且假设它们位于腺苷钴胺结合位点。

Methionine synthase: homocystinuria and neurologic dysfunction 蛋氨酸合成酶:同晶体尿症与神经功能障碍

Methionine synthase (5-methyltetrahydrofolate–homocysteine S-methyltransferase) catalyzes the cobalamin-dependent methy-lation of homocysteine, using 5-methyltetrahydrofolate as the methyl donor (see OMIM 156570). Defects in methionine synthase result in hyperhomocysteinemia and are implicated as the lesion in the cblG complementation group of disorders in cobalamin metabolism (294).

蛋氨酸合酶(5-甲基四氢叶酸-同型半胱氨酸S-甲基转移酶)催化同型半胱氨酸依赖钴胺的方法,以5-甲基四氢叶酸为甲基供体(see OMIM 156570).蛋氨酸合成酶缺陷导致高同型半胱氨酸血症并被认为是钴胺代谢紊乱cblG互补群中的病变。

The cblG group generally has reduced methionine synthase activity even under optimal conditions; thus, primary defects in the catalytic subunit of the enzyme may be responsible for this subgroup. The cblG group shows biochemical heterogeneity with respect to the binding of cellular cobalamin to methionine syn-thase. In extracts of cell lines from most patients, the methyltrans-ferase binds 75% of cellular cobalamin, even though little of it is methylcobalamin. In a few lines, however, the methyltransferase is devoid of bound cobalamin of any form. This suggests the presence of mutations in the cobalamin binding domain of the methyltransferase, strengthening the possibility that the cblG group results from primary deficiencies in the methionine synthase apoenzyme (295). Hydroxycobalamin should be instituted (1 mg/d intramuscularly initially, then tapered to 1–3 mg/wk) as soon as the disorder is diagnosed (295).

在最适条件下,cblG组的蛋氨酸合成酶活性普遍降低;因此,酶的催化亚基中的主要缺陷可能是导致这一亚基的原因。cblG组在细胞钴胺与蛋氨酸合成酶结合方面表现出生化异质性。在大多数患者的细胞提取物中,甲基转铁酶结合了75%的细胞钴胺,在大多数患者的细胞提取物中,甲基转铁酶结合了75%的细胞钴胺,然而,在一些品系中,甲基转移酶没有任何形式的结合钴胺。这表明甲基转移酶钴胺结合区存在突变,增强cblG群由蛋氨酸合成酶载脂蛋白酶的主要缺陷引起的可能性。羟基钴胺素应设立(最初肌肉注射1mg/d,然后逐渐变细至1-3mg/wk)一旦这种疾病被诊断出来。

Early treatment of methylcobalamin deficiency may prevent major neurologic complications of these diseases. One child who received hydroxycobalamin therapy before and after birth devel-oped cognitively normally (296).

早期治疗甲钴胺缺乏可以预防这些疾病的主要神经并发症。一名在出生前和出生后接受羟钴胺治疗的儿童恢复了正常的认知能力

TABLE 7 Enzymes that use a biotin cofactor1 使用生物素辅助因子的酶

Defective enzyme and EC no.
Localization
Reaction catalyzed
Disease or condition
OMIM no.
Inheritance
Holocarboxylase synthetase 羧化全酶合成酶(6.3.4.10)
Cytoplasmic and mitochondrial
细胞质和线粒体
Apocarboxylases + biotin →holocarboxylases
Multiple carboxylase deficiency, 多羧化酶缺乏症
metabolic acidosis,
代谢性酸中毒 hypotonia,seizures, 张力减退,癫痫,and lethargy (sometimes developmental delay or coma) 昏睡(有时发育迟缓或昏迷)
253270
Autosomal recessive
常染色体隐性
1 OMIM, Online Mendelian Inheritance in Man (4).

TABLE 8
Enzymes that use an adenosylcobalamin or methylcobalamin cofactor1

Defective enzyme and EC no.
Localization
Reaction catalyzed
Disease or condition
OMIM no.
Inheritance
Methylmalonyl-CoA mutase (5.4.99.2)
甲基丙二酰-CoA 变位酶
Mitochondrial
线粒体
Isomerization of methylmalonyl-CoA → succinyl-CoA
Methylmalonic acidemia, 甲基丙二酸血症,metabolic ketoacidosis, 代谢性酮症酸中毒 and cognitive dysfunction
认知功能障碍
251000
Autosomal recessive
常染色体隐性
Methionine synthase (2.1.1.13)蛋氨酸合成酶
Cytoplasmic
细胞质
Homocysteine + 5-methyl-THF → methionine + THF
Homocystinuria, 高胱氨酸尿,failure to thrive,发育迟缓 and neurologic complications神经学并发症;
156570
Autosomal recessive常染色体隐性
Methionine synthase reductase (2.1.1.135)
蛋氨酸合成酶还原酶
Cytoplasmic?
细胞质
MS-cob(II)alamin + NADPH + SAM → MS-methylcob(I)alamin + S-adenosylhomocysteine + NADP
Homocystinuria and mental retardation
高胱氨酸尿和智力迟钝
602568
Autosomal常染色体的
1 MS, methionine synthase; OMIM, Online Mendelian Inheritance in Man (4); SAM, S-adenosylmethionine; THF, tetrahydrofolate.

Of 2 patients described in another study, the first had greatly diminished steady state levels of methionine synthase mRNA (297). The biochemical data on the second patient’s cell line (cblG WG1892) implicated mutations in the carboxyl-terminal S-adeno-sylmethionine binding domain and the intermediate cobalamin binding domain. Two mutations were detected in cblG WG1892: the conversion of a conserved proline (1173) to a leucine residue and a deletion of an isoleucine residue (881). The investigators concluded, “The crystal structure of the C-terminal domain of the E. coli methionine synthase predicts that the proline to leucine mutation could disrupt activation since it is embedded in a sequence that makes direct contacts with the bound S-adenosyl-methionine. Deletion of isoleucine in the B12-binding domain would result in shortening of a -sheet. Our data provide the first evidence for mutations in the methionine synthase gene being culpable for the cblG phenotype. In addition, they suggest directly that mutations in methionine synthase can lead to elevated homocysteine, implicated both in neural tube defects and in cardiovas-cular diseases” (297).

在另一项研究中描述的2名患者中,第一次大幅度降低了蛋氨酸合成酶mRNA的稳态水平。第二病人细胞系的生化指标(CblG WG1892)羧基端S-腺苷-三甲基氨酸结合域的连锁突变和中间钴胺结合域。在cblG WG1892中检测到两个突变:保守的脯氨酸(1173)转化为亮氨酸残基和异亮氨酸残基的缺失。调查人员得出结论,“大肠杆菌蛋氨酸合成酶C末端结构域的晶体结构预测,脯氨酸向亮氨酸突变可能破坏激活,因为它嵌入在一个序列中直接与S-腺苷甲硫氨酸结合。B_(12)结合区异亮氨酸的缺失将导致a-片的缩短.我们的数据提供了第一个证据表明蛋氨酸合成酶基因的突变是cblG表型的罪魁祸首。他们直接暗示蛋氨酸合成酶的突变会导致同型半胱氨酸升高,既与神经管缺陷有关,也与心脏疾病有关“

Two methionine synthase mutations that are candidates for causing the cblG disease are located in the vicinity of the cobalamin binding domain: one is the same deletion of isoleucine 881 mentioned above; the other is amino acid substitution His920→Asp. A polymorphism, Asp919→Gly (resulting from 2756A→G, mutant allele frequency 15%), was identified at an adjacent residue, and thus may also be near or in the cobalamin binding site (298). The polymorphism has been associated with lower plasma homocysteine concentrations (299, 300), which is puzzling and suggests that this polymorphism, which has been postulated to modify an amino acid on a helix involved with cofactor binding, is an activating mutation.

引起cblG病的两个蛋氨酸合成酶突变位于钴胺结合区附近:一是上述异亮氨酸881的缺失;另一种是氨基酸取代His 920→Asp.一个多态性,Asp919→Gly(由2756A→G引起,突变等位基因频率为15%),在邻近的残基上被识别,因此也可能在钴胺结合位点附近或附近。该多态性与血浆同型半胱氨酸浓度降低有关。这是一个令人费解的问题,表明这种多态是一种激活的突变,这种多态被认为是为了修饰一个与辅因子结合有关的螺旋上的一个氨基酸。

Of 2 unrelated boys with a cblG defect due to methionine synthase deficiency, one improved immediately on switching to hydroxycobalamin from cyanocobalamin (which caused respira-tory depression and lethargy in the patient). It appears that treat-ment with intramuscular injections of hydroxycobalamin alleviates megaloblastic anemia and stabilizes neurologic deterioration in children with the cblG defect but may not completely correct hypotonia and developmental delay or improve the anorexia or poor weight gain associated with cblG disease (301).

在两个没有血缘关系的男孩中,蛋氨酸合成酶缺乏症导致cblG缺陷,从氰钴胺转到羟基钴胺后立即改进了一种(这导致了病人的呼吸-)肌肉注射羟钴胺可减轻巨幼细胞性贫血并稳定患有cblG缺陷的儿童的神经功能恶化但可能不能完全纠正肌张力低下和发育迟缓,或改善与cblG病相关的厌食症或体重增长不良。

Ample evidence seems to suggest that defects in methionine synthase can account for some cblG patients. Some mutations appear to affect cobalamin binding and thus serve as an explanation for the response to cobalamin in some patients. There is also evidence that the cblG complementation group is heterogeneous (302).

大量的证据似乎表明蛋氨酸合成酶的缺陷可以解释一些cblG患者。一些突变似乎会影响钴胺结合从而可以解释某些病人对钴胺的反应。也有证据表明,cblg互补组是异构的。

Methionine synthase reductase: homocystinuria and mental retardation 蛋氨酸合成酶还原酶:高胱氨酸尿和智力迟钝

Methionine synthase reductase [MSR; (methionine syn-thase)–cobalamin methyltransferase (cob(II)alamin reducing)] is responsible for the reductive methylation and reactivation of methionine synthase with S-adenosylmethionine as a methyl donor (see OMIM 602568). MSR is a member of the ferredoxin-NADP reductase family of electron transferases, containing the FMN, FAD, and NADPH binding sites necessary to maintain methionine synthase in its functional state.

蛋氨酸合成酶还原酶[MSR;(蛋氨酸合成酶)-钴胺甲基转移酶(COB(II)AlaminReduction)]以S-腺苷甲硫氨酸为甲基供体,负责蛋氨酸合成酶的还原甲基化和重新激活(见OMIM 602568)。MSR是铁氧还蛋白-NADP还原酶家族中的一员,含有FMN、FAD和NADPH结合位点,是维持蛋氨酸合成酶功能状态所必需的。

MSR deficiency is associated with the cblE complementation group of cobalamin deficiencies. Over time, the highly reactive cobalamin(I) cofactor of methionine synthase is oxidized to the inert cobalamin(II) form, rendering the enzyme inactive (294). Symptoms of MSR defects include microcephaly, psychomotor retardation, episodic reduced consciousness, megaloblastic anemia, increased plasma free homocysteine (> 20 mol/L), low plasma methionine (< 10 mol/L), and increased excretion of formiminoglutamate.

MSR缺乏症与钴胺缺乏症的cblE互补组有关。随着时间的推移,高活性钴胺(I)蛋氨酸合成酶的辅助因子被氧化成惰性钴胺(II)形式,使酶失活.MSR缺陷的症状包括小头畸形、精神运动性迟滞、间歇性意识减退、肥大型Mia、血浆游离同型半胱氨酸升高(>20 mol/L),低血浆蛋氨酸(<10 mol/L),增加甲酰谷氨酸的排泄。

In one case report, a female patient with MSR deficiency was treated with several vitamins and cofactors and her clinical progress was followed for 17 y (303). With high-dose folic acid treatment, biochemical abnormalities such as formiminogluta-mate excretion and homocystinuria nearly normalized, but clinical and hematologic abnormalities remained. When folate was replaced by methylcobalamin, alertness, motor function, speech, and electroencephalogram results improved and biochemical features were similar but mean corpuscular volume increased. The best control of symptoms was observed with a combination of folate and methylcobalamin. At the age of 17 y, the patient remained severely mentally retarded. In cultured fibroblasts, methionine synthesis was reduced to 0.03 nmol · mg1 · 16 h1 compared with control values of 2.4–6.9 nmol · mg1 · 16 h1. Complementation studies indicated the cblE defect. These studies suggest a role for folate in addition to cobalamin in treatment (303).

在一个案例中,1例女性MSR缺乏症患者应用多种维生素和辅助因子治疗,随访17岁。用高剂量的叶酸治疗,生化异常,如甲酰胺酶-配偶排泄物高胱氨酸尿几近正常化,但临床和血液学异常仍然存在。当叶酸被甲钴胺替代时,警觉性、运动功能、言语和脑电图结果有所改善,生化特征相似,但平均红细胞体积增加。以叶酸和甲钴胺联合治疗症状效果最好。在17岁的时候,在17岁的时候,在培养的成纤维细胞中,蛋氨酸合成降低到0.03nmol·mg1·16H1,而对照值为2.4-6.9nmol·mg1·16H1。互补研究表明了cblE缺陷。这些研究表明叶酸在治疗中除了钴胺外还有作用。

The standard therapy consists of parenterally administered hydroxycobalamin (1–3 mg/wk) but not cyanocobalamin, and sometimes the additional administration of folic acid and betaine. The oldest known patient was first diagnosed with cblE disease at the age of 25 y (304). He had megaloblastic anemia at the age of 7 wk, which was treated with hydroxycobalamin (500 g/d) and folic acid (5 mg/d) for 5 d, resulting in a prompt rise in hemoglobin concentrations even though megaloblastosis persisted. The therapy was continued with 1 mg cyanocobalamin intramuscularly every 8 wk and 5 mg folic acid /d orally. During the following months, he showed progressive neurologic deficits including developmental delay, pigmentary retinopathy, nystagmus, and seizures. Despite intensified therapy, the neurologic symptoms progressed. The therapy was changed to parenteral administration of hydroxycobalamin (1 mg twice a week), which, over a period of 5 mo, resulted in a normalization of methionine concentrations and a reduction in homocysteine concentrations but did not influence the neurologic symptoms.

标准疗法包括肠外注射羟钴胺(1-3毫克/周),但不含氰钴胺,有时补充叶酸和甜菜碱。已知年龄最大的病人在25岁时首次被诊断患有cblE病。他7周时患有巨幼细胞性贫血,用羟钴胺(500 g/d)和叶酸(5mg/d)治疗5d,导致血红蛋白浓度迅速上升,即使巨细胞增生持续存在。每8wk肌注氰钴胺1mg,口服叶酸5mg。在接下来的几个月里,他表现出进行性神经功能缺陷,包括发育迟缓,色素性视网膜病变,眼球震颤和癫痫。尽管加强了治疗,但神经症状仍有进展。治疗改为肠外注射羟钴胺(每周1毫克,每周两次),在5年的时间里,导致蛋氨酸浓度正常化,同型半胱氨酸浓度降低,但不影响神经系统症状。

Characterization of defects in cblE patients showed several mutations in the gene encoding MSR. Of the 11 mutations identified in one study, 3 were nonsense mutations (294). The remaining 8 mutations were found throughout the coding region and involved substitutions or in-frame disruptions of the coding sequence. Of 7 mutations not identified in the control population, 3 were located in the vicinity of the proposed FMN binding site and 2 more were found to be associated with the FAD and NADPH binding regions.

cblE患者的缺陷特征显示了编码MSR基因的几个突变。在一项研究中发现的11种突变中,有3种是无意义的突变。其余8个突变出现在整个编码区,涉及编码序列的替换或帧内破坏。在对照人群中没有发现的7个突变中,3处位于拟议的FMN结合位点附近,2条与FAD和NADPH结合区相关联。

Cobalamin treatment seems to bypass the genetic defect because MSR does not use a cobalamin cofactor. We suggest that physicians consider the benefits of riboflavin, the precursor to FMN and FAD, and niacin, the precursor of NADP, in addition to cobalamin and folate when treating patients with cobalamin disorders.

钴胺治疗似乎绕过了基因缺陷,因为MSR不使用钴胺辅助因子。我们建议医生考虑核黄素的好处,FMN和FAD的前体,NADP的前体烟酸,以及钴胺和叶酸治疗钴胺紊乱的患者。

Tissue concentrations and toxicity 组织浓度和毒性
There is no defined UL for cobalamin and cyanocobalamin 钴胺和氰钴胺没有明确的UL
(the form used in the United States and Canada). Therapy has resulted in few adverse effects with doses ≤ 5000 μg/d (7).(在美国和加拿大使用的形式)。使用剂量为≤5000μg/d的药物治疗几乎没有副作用。

FOLIC ACID 叶酸
The DRI for folic acid is 400 g/d (7). 叶酸的DRI为400 g/d

The crystal structure of a folate binding enzyme (dihydrofolate reductase) complexed with folate has been solved to 2.3 Å and residues that directly interact with folate have been identified (305). The folate-dependent enzymes are summarized in Table 9.

叶酸结合酶的晶体结构(二氢叶酸还原酶)与叶酸的络合已被解离为2.3,Å已经确定了与叶酸直接相互作用的残留物(305)。表9概述了叶酸依赖酶.

Methylenetetrahydrofolate reductase (NADPH): homocysteinemia, schizophrenia, rages, depression, central nervous system dysfunction, and neural tube defects

亚甲基四氢叶酸还原酶(NADPH):高胱氨酸血,精神分裂症、狂怒、抑郁、中枢神经系统功能障碍和神经管缺陷.

MTHFR (also discussed in the section on riboflavin) cat-alyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate (see OMIM 236250). The latter is the predominant circulatory form of folate and the main carbon donor for the remethylation of homocysteine to methion-ine. Patients with severe MTHFR deficiency (0–20% residual activity) present in infancy or adolescence with developmental delay, motor and gait dysfunction, seizures, schizophrenic disturbances, and other neurologic abnormalities; they are also at risk of vascular complications. MTHFR mutations, including the 677C→T polymorphism, lead to elevated plasma homo-cysteine concentrations, a risk factor for vascular disease and possibly schizophrenia.

MTHFR(也在核黄素一节中讨论)CAT-分析了5,10-亚甲基四氢叶酸转化为5-甲基四氢叶酸(见OMIM 236250)。后者是叶酸的主要循环形式是同型半胱氨酸再甲基化的主要碳供体。严重MTHFR缺乏症(0-20%残留活动)的患者在婴儿期或青春期出现发育迟缓,运动和步态障碍,癫痫发作,精神分裂,以及其他神经功能异常;他们也有血管并发症的危险。MTHFR突变,包括677c→T多态性,导致血浆同型半胱氨酸浓度升高,这是血管疾病和精神分裂症的危险因素。

Recurrent episodes of folate-responsive schizophrenic-like behavior were documented in a mildly retarded adolescent girl with homocystinuria and homocysteinemia without hyperme-thioninemia who lacked the habitus associated with CBS deficiency (306). Enzymes involved in homocysteine-methionine metabolism were shown to be normal. A defect in the ability to reduce 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofo-late was shown and MTHFR activity was 18% of control values. The girl was treated with oral folic acid and all her psychotic behavior ceased. Supplementation with folic acid (20 mg/d) for 14 d led to a decrease in homocysteine excretion and progressive improvement in intellectual function over the next 3 mo without further medication. The girl left the hospital without medication and was readmitted later, at which point folic acid and vitamin B-6 induced major improvements again. This is one of 4 patients described since 1975 (307).

MTHFR突变,包括677c→T多态性,导致血浆同型半胱氨酸浓度升高,这是血管疾病和精神分裂症的危险因素。同型半胱氨酸-蛋氨酸代谢相关的酶被证明是正常的.降低5,10-亚甲基四氢叶酸为5-甲基四氢叶酸的能力存在缺陷,MTHFR活性为对照值的18%。这个女孩接受了口服叶酸的治疗,她的所有精神病行为都停止了。补充叶酸(20毫克/天)14天,可减少同型半胱氨酸的排泄,并逐步改善。在未来3mo的智力功能,不需要进一步的药物治疗。女孩没有用药就离开了医院,后来又被重新入院,这时叶酸和维生素B6又引起了很大的改善。这是1975年以来描述的4个病人中的一个。

Two children who were found to have homocystinuria after they were examined for rages and seizures were initially thought to have a biochemical defect in the conversion of homocysteine to methionine. They both responded favorably to low-dose folic acid (0.8–3 mg/d) with a decrease in urinary homocystine and other improvements, but the benefits only lasted several months, at which time homocystine concentrations increased and rages resumed. In one case, double the amount of folate and a low-protein diet caused improvement; in the other, betaine and a low-protein diet were effective. The authors suggested that the biochemical defect was a deficient MTHFR activity that is par-tially responsive to folate therapy (308).

两名儿童在被检查为狂怒和癫痫发作后发现有同频尿症,最初被认为在同型半胱氨酸转化为甲硫氨酸方面存在生化缺陷。它们对低剂量的叶酸都有很好的反应 (0.8–3 mg/d)随着尿同型晶体的减少和其他方面的改善,但福利只持续了几个月,此时,同型晶体浓度增加,狂暴再次出现。在一种情况下,两倍量的叶酸和低蛋白饮食导致改善;另一方面,甜菜碱和低蛋白饮食是有效的.作者认为,生物化学缺陷是MTHFR活性不足,对叶酸治疗的反应是正常的。

The Km of the E. coli mutant protein homologous to the human 677C→T variant was measured and found to not differ significantly from controls (165). FAD binding was affected—likely as a result of an increased Km for the coenzyme—but the decreased affinity of MTHFR for FAD was abolished under conditions of high folate. It was thus hypothesized that folic acid therapy low-ers homocysteine in TT individuals by increasing enzyme affinity for FAD. FAD binding is similarly impaired in the recombinant human enzyme, which was recently purified (164). The more severe cases discussed above may have responded to folate through increases in enzyme affinity for FAD or by overcoming a decreased affinity for the folate substrate itself.

测定了与人677c→T变异体同源的大肠杆菌突变蛋白的Km值并发现与对照组相比并无显著差异。FAD结合受到影响-可能是辅酶KM增加的结果-但MTHFR与FAD的亲和力降低在高叶酸条件下被取消。因此,假设叶酸治疗TT个体的低水平同型半胱氨酸是通过增加酶对FAD的亲和力来实现的。FAD结合在重组人酶中也同样受损,最近被净化了.以上讨论的更为严重的病例可能通过增加对FAD的酶亲和力或通过克服对叶酸底物本身的亲和力降低而对叶酸作出反应。

Another reason for lowering homocysteine concentrations by riboflavin, vitamin B-12, folate, and vitamin B-6 supplementation is the reduction of anger and hostility. Positive and significant associations were reported between hostility and homocysteine concentrations in both men and women and between anger and homocysteine concentrations in men (309).

另一个降低同型半胱氨酸浓度的原因是核黄素、维生素B-12、叶酸和维生素B-6的补充减少了愤怒和敌意据报道,男性和女性的敌对状态和同型半胱氨酸浓度以及男性的愤怒和同型半胱氨酸浓度之间存在显著的正相关关系。

The 677C→T polymorphism in MTHFR was examined in persons with schizophrenia, major depression, and bipolar disor-der (310). The TT variant was found in 12% of 419 control subjects, 21% of 297 patients with schizophrenia (P < 0.0006; P < 0.002 after Bonferroni correction), 28% of 32 patients with major depression (P < 0.06; P < 0.02 after Bonferroni correc-tion), and 13% of 40 patients with bipolar disorder (NS). The authors pointed out that the oxidation product of homocysteine, homocysteic acid, exerts potent excitatory effects (310). Joober et al (311) also found an overrepresentation of the TT variant in persons with schizophrenia who responded to neuroleptics compared with that in control subjects (311).

检测了精神分裂症、重度抑郁症和双相情感障碍患者MTHFR 677c→T多态性。419例正常人中TT变异率为12%,在297例精神分裂症患者中为21%(P<0.0006;P<0.002)。32例重度抑郁症患者中28%(P<0.06;P<0.02),40例双相情感障碍(NS)患者中占13%。作者指出,同型半胱氨酸的氧化产物-同型半胱氨酸-具有很强的兴奋性作用。Joober等人,在精神分裂症患者中,与对照组相比,对抗精神病药物有反应的精神分裂症患者中TT变异的比例也过高。

In another study, high homocysteine concentrations were found in 9 of 20 patients with schizophrenia (312). The thermolabile 677C→T polymorphism was screened for in a follow-up study of 11 patients with high homocysteine concentrations. Seven of the 11 patients, 6 males and 1 female, had the homozygous TT geno-type. One male patient was heterozygous and all 3 normal homozygotes were females. In the patients who were homozygous for the polymorphism, homocysteine concentrations did not respond to vitamin B-12 but were normalized by folate supple-mentation. In the healthy homozygotes, however, homocysteine concentrations were reduced by vitamin B-12 alone. It was concluded that homozygosity for thermolabile MTHFR may be a risk factor for schizophrenia-like psychosis, and that this risk might be reduced by folate supplementation (313). In a small study (314), homocysteine was significantly higher in patients with schizo-phrenia who had low serum folate concentrations (n = 6) than in control subjects with low serum folate concentrations (n = 8).

在另一项研究中,20例精神分裂症患者中有9例发现高同型半胱氨酸。在11例高同型半胱氨酸患者的随访研究中,筛选了热摩尔677c→T多态性。11名病人中有7名,其中男性6例,女性1例,均为纯合子TT Geno型。1例男性为杂合子,3例正常纯合子均为女性。在多态纯合子的患者中,同型半胱氨酸浓度对维生素B-12没有反应,而是通过叶酸的增强而正常化。然而,在健康的纯合子中,纯半胱氨酸浓度仅靠维生素B1 2就降低了.结论:热摩尔mtfr纯合子可能是精神分裂样精神分裂症的危险因素,补充叶酸可降低此风险。在一个小的研究中,血清叶酸浓度较低的分裂性膈病患者(n=6)的同型半胱氨酸明显高于低血清叶酸浓度的正常人(n=8)。

Two reports did not find a link between schizophrenia, the 677C→T polymorphism, and hyperhomocysteinemia. In one report, no significant difference in the frequency of TT individu-als was found between the 343 patients with schizophrenia and 258 control subjects studied. It was concluded that the 677C→T polymorphism is unlikely to have played a major role in the pathogenesis of schizophrenia or affective disorders in the sample population (315). Another group found no significant differences in plasma homocysteine concentrations between the 210 patients with schizophrenia and 218 control subjects stud-ied. The distributions of the T allele and TT genotype frequencies were similar in both groups (40% and 15%). Thus, it was con-cluded that impaired homocysteine metabolism is unlikely to play a role in schizophrenia (316).

两份报告没有发现精神分裂症之间的联系,677c→T多态性,高同型半胱氨酸血症。在一份报告中,343名精神分裂症患者和258名对照者TT不可分割-ALS的频率没有显着性差异。结果表明,677c→T多态性不太可能在精神分裂症或情感障碍的发病中起重要作用。另一组患者的血浆同型半胱氨酸浓度在210名精神分裂症患者和218名对照组之间没有显着性差异。T等位基因和TT基因型频率在两组间分布相似(分别为40%和15%)。因此,同型半胱氨酸代谢受损不太可能在精神分裂症中起作用。

We suggest that clinical trials of B vitamin therapy (including folate and riboflavin) in relation to schizophrenia and rages are warranted on the basis of the association of higher homocysteine concentrations with anger (309) and schizophrenia (312) and the association of the TT genotype with schizophrenia (310). Homocysteine accumulation can be an indicator of a defective enzyme in the methylation pathway and treatment with vitamin precursors of substrates and cofactors in that pathway such as riboflavin, vitamin B-12, folate, and vitamin B-6 may be benefi-cial in managing rages and schizophrenia.
我们建议B类维生素治疗的临床试验(包括叶酸及核黄素)与精神分裂症和愤怒有关的依据是高同型半胱氨酸浓度与愤怒的关系和精神分裂症,TT基因型与精神分裂症的关系。同型半胱氨酸的积累可能是甲基化途径中有缺陷的酶的一个指标和用底物的维生素前体处理以及在这一途径中的辅助因子,如核黄素,维生素B-12、叶酸和维生素B-6可能有助于治疗愤怒和精神分裂症.

Folate is a well-established measure for preventing NTDs. Various studies have implicated the 677C→T mutation and high homocysteine in NTDs and others have shown a decrease in NTD prevalence in mothers who take folic acid perinatally (317). Although the etiology of NTDs is likely multifactorial and 677C→T alone is certainly not responsible for NTDs, a possible explanation for folate-responsiveness in individuals with the polymorphism could relate to the fact that incubation of the variant enzyme with high concentrations of folate abolishes the reduced FAD binding capacity of 677C→T MTHFR (165). It is unclear whether perinatal use of riboflavin, the precursor of FAD, would be of additional benefit for some mothers at risk of delivering a child with an NTD.

叶酸是预防NTDs的一种行之有效的措施.各种研究都暗示了677c→T突变和高同型半胱氨酸在NTDs中的存在还有一些研究表明,在围产期服用叶酸的母亲中,NTD的患病率有所下降。虽然NTDs的病因可能是多因素和677c的,但单是→T并不是NTDs的病因。这种多态个体对叶酸反应性的一个可能解释可能与叶酸浓度高的变异酶孵育可消除r有关。677c→T MTHFR的FAD结合能力,目前尚不清楚围产期使用核黄素(FAD的前身)是否会对一些有可能接生NTD儿童的母亲带来额外的好处。

Methionine synthase: homocystinuria and neurologic dysfunction 蛋氨酸合成酶:高胱氨酸尿和神经功能障碍

One patient with 36% of normal residual methionine synthase activity improved significantly with folic acid treatment (318). (See OMIM 156570 and the section on cobalamin for further information on methionine synthase.)

1例残馀36%蛋氨酸合成酶活性正常的患者经叶酸治疗后明显改善(关于蛋氨酸合成酶的进一步信息,请参阅OMIM 156570和钴胺一节。)。

Dihydrofolate reductase: megaloblastic anemia and neurologic symptoms
二氢叶酸还原酶:巨幼细胞性贫血与神经系统症状

Dihydrofolate reductase uses NADPH to catalyze the successive reductions of folate to 7,8-dihydrofolate to 5,6,7,8-tetrahydro-folate (see OMIM 126060). In one patient with megaloblas-tic anemia and decreased enzymatic activity, oral folic acid (5 mg/d) resulted in a sustained 3-y remission (500 g/d had no effect) (319). When folate therapy was discontinued, the patient relapsed.

二氢叶酸还原酶利用NADPH催化将叶酸连续还原成7,8-二氢叶酸为5,6,7,8-四氢叶酸(见OMIM 126060)。1例巨幼细胞性贫血患者酶活性降低,口服叶酸(5mg/d)可持续缓解3~y(500 g/d)。当叶酸治疗停止时,病人又复发了。

Dihydrofolate reductase deficiency was reported in 3 children presenting with a megaloblastic anemia shortly after birth (320). A deoxyuridine suppression test was abnormal in 2 of the children and was only corrected with folinic acid, 5-formyltetrahy-drofolate. A hematologic response was also evident after folinic acid therapy, although this therapy may bypass the defect.

3例出生后不久出现巨幼细胞性贫血的儿童报告了二氢叶酸还原酶缺乏症。2例患儿脱氧尿苷抑制试验异常,仅用叶酸纠正,5-甲酰基四氢叶酸。叶酸治疗后的血液学反应也很明显,尽管这种治疗可以绕过缺陷。

Glutamate formiminotransferase: mental retardation Glutamate formiminotransferase uses PLP to transfer the formimino group from formimino glutamate to tetrahydrofolate to form 5-formyltetrahydrofolate (folinic acid). A defect in this enzyme results in excretion of formimino glutamate (see OMIM 229100). Four of 5 original patients reported by Arakawa (321) had mental and physical retardation; enzymatic activity ranged from 14% to 54% of normal.

谷氨酸亚胺甲基转移酶:智力缺陷谷氨酸亚胺甲基转移酶使用PLP将甲酰亚胺基从谷氨酸甲酰转移到四氢叶酸,形成5-甲酰四氢叶酸(叶酸)。这种酶的缺陷导致谷氨酸甲醛的排泄(见OMIM 229100)。Arakawa报告的5名原始患者中有4人(321人)有智力和身体发育迟缓;酶活性为正常人的14%~54%。
Five additional patients were reported with the deficiency; one was a 42-y-old woman whose elevated urinary concentrations of formiminoglutarate fell to normal with 30 mg folic acid/d and who improved with continued folate therapy (322). As measured by decreased excretion of formimino glutamate, 2 of 8 patients responded to treatment with high folic acid (323, 324).
另有5名患者报告患有这种缺乏症;其中一位42岁的女性,每天服用30毫克叶酸后,尿中的甲胺磷已降至正常水平和继续叶酸治疗改善。8例患者中有2例用高叶酸治疗,以减少谷氨酸的排泄量为指标。

Physicians might consider treatment with pyridoxine (cofactor precursor) in addition to folate (substrate precursor) in patients who present with a defect in glutamate formiminotrans-ferase. Folinic acid therapy, which would bypass the metabolic defect, should be effective as well.

医生可能会考虑用吡多辛治疗(辅因子前体)除了叶酸(底物前体)在出现谷氨酸甲酰转铁酶缺陷的病人中。叶酸治疗,可以绕过代谢缺陷,也应该是有效的。

Folate membrane transport: dyserythropoiesis, central nervous system dysfunction, and megaloblastic anemia Congenital malabsorption of folate (see OMIM 229050) results clinically in hypotonia, lethargy, seizures, megaloblastic anemia, mental retardation, and ataxia and biochemically in low folate concentrations in serum, red blood cells, and cere-brospinal fluid (320). A patient with hereditary dyserythropoiesis (without anemia) had reduced membrane transport of 5-methyltetrahydrofolate by red blood cells (325). Total uptake, uptake velocity, and maximal velocity of uptake were all significantly less than in control subjects. The patient’s measured Km was 0.27 mol/L (Vmax 0.095 pmol · 109 cells · min1) whereas that in control subjects was 0.50 mol/L (Vmax 0.301 pmol · 109 cells · min1). Although the Vmax was lower in the patient, the Km did not appear to be the primary defect. However, the patient’s daughter had an elevated Km of 0.93 mol/L, suggesting a reduced affinity of the transport sys-tem for 5-methyltetrahydrofolate.

叶酸膜转运:异常红系造血,中枢神经系统功能障碍,和巨幼细胞贫血先天性叶酸吸收不良(see OMIM 229050) 结果临床表现为低张力,嗜睡、癫痫、巨幼细胞性贫血,智力迟钝,共济失调和低浓度叶酸在血清、红细胞和脑脊液中的生物化学含量。1例遗传性甲状腺发育不良(无贫血)患者红细胞减少了5-甲基四氢叶酸的膜转运。总摄取、摄取速度和最大摄取速度均明显低于对照组。患者的Km值为0.27mol/L(Vmax为0.095 pmol·109个细胞·min1),对照组为0.50mol/L(Vmax为0.301 pmol·109个细胞·min1)。虽然Vmax在患者中较低,但Km并不是主要的缺陷。然而,病人的女儿的KM升高了0.93 mol/L,表明Tran的亲和力降低了5-甲基四氢叶酸的运动系统。

Four cases of congenital malabsorption of folate with megaloblastic anemia, central nervous system abnormalities, and defec-tive gastrointestinal absorption of folates responded at least partially to folic acid (40 mg oral) (322). A review of folate meta-bolic errors states that 12 cases of defective transport of folate across the intestine and the blood-brain barrier have been reported. High doses of oral folic acid (5–40 mg) or lower parenteral doses can reverse the hematologic abnormalities and digestive symp-toms involved with the condition (320). A Km explanation is not definitive because transport of folate through an alternative system at high concentrations has not been ruled out.

先天性叶酸吸收不良伴巨幼细胞性贫血4例,中枢神经系统异常,叶酸的胃肠道吸收不良反应至少部分是叶酸(40毫克口服)。对叶酸代谢错误的回顾指出,有12例叶酸在肠道和血脑屏障中的转运缺陷。大剂量的口服叶酸(5-40毫克)或较低剂量的肠系膜外剂量可以逆转血液学异常和与此相关的消化异常。KM的解释并不明确,因为不排除通过高浓度替代系统运输叶酸的可能性。

Seizures 癫痫发作

Folinic acid has been used in treating early-onset intractable seizures (unresponsive to anticonvulsants and pyridoxine) and can elicit an immediate response (326).
叶酸已被用于治疗早期顽固性发作(对抗惊厥药和吡多辛没有反应),并能立即引起反应


Folylpoly--glutamate carboxypeptidase: homocysteinemia Folylpoly--glutamate carboxypeptidase (-glutamyl hydro-lase), an enzyme that is anchored to the intestinal brush border membrane, is responsible for cleaving terminal glutamate residues from folylpoly--glutamates (see OMIM 600934), the predominant naturally occurring form of dietary folates. Inabil-ity to cleave glutamyl residues reduces the intestinal absorption of folates and decreases folate availability for the remethyla-tion of homocysteine to methionine (see the discussion of methionine synthase in the section on cobalamin), resulting in hyperhomocysteinemia.
叶酸聚谷氨酸羧肽酶:同型半胱氨酸血症叶酸聚,谷氨酸羧肽酶,一种锚定在肠刷边界膜上的酶,是一种有效的酶。可用于从叶酸中切割末端谷氨酸残基(见OMIM 600934),这是膳食叶酸的主要自然存在形式。酶解谷氨酰基残留量减少叶酸的肠道吸收,降低叶酸对同型半胱氨酸再甲基化为甲硫氨酸的有效性(见关于钴胺的一节中关于蛋氨酸合成酶的讨论),RES。高同型半胱氨酸血症。

A C-to-T transition at base pair 1561 was found in 6 (8%) of 75 healthy individuals (327). The polymorphism causes a mis-sense mutation, His475→Tyr that decreases protein activity by 53% as measured in transfected COS-7 cells. As expected, indi-viduals with the polymorphism (heterozygotes) have lower serum folate and higher homocysteine (significant) concentrations and lower red blood cell folate concentrations (NS). Such individuals may benefit from folate supplementation through raised body folate concentrations and lowered homocysteine. This therapy would likely bypass the defect because supplements contain the monoglutamate form of folate and thus do not require the action of folylpoly--glutamate carboxypeptidase. Nevertheless, it would be of interest to measure the kinetic properties of the enzyme as well as the ability of exogenous polyglutamate-folates to over-come the defect.

在75名健康人中,有6人(8%)在1561碱基对处发现C-to-T转变。该多态性导致一个错误的突变,His475→Tyr,降低53%的蛋白质活性,在转染的COS-7细胞。与预期一样,具有多态性(杂合子)的个体具有较低的血清叶酸和较高的同型半胱氨酸浓度(显著)和较低的红细胞叶酸浓度(NS)。这些人可能通过提高体内叶酸浓度和降低同型半胱氨酸而受益于补充叶酸。这种疗法可能会绕过缺陷,因为补充剂含有叶酸的单谷氨酸形式,因此不需要叶酸聚-谷氨酸羧肽酶的作用。然而,测定该酶的动力学性质以及外源性谷氨酸-叶酸克服缺陷的能力是很有意义的。

Tissue concentrations and toxicity 组织浓度和毒性

A UL for folate intake from supplements and fortified foods has been set at 1000 g/d for adults and 300 g/d for 2-y-olds increasing to 800 g/d for 16-y-olds (7), although higher amounts seem warranted in many cases. One patient mentioned above had serum folate concentrations of 185 mg/L (normal con-centrations are 6 g/L) and red blood cell folate concentrations of 591 mg/L (normal concentration: 160 g/L) after 4 mo of supplementation with 12 mg folic acid/d (325). A recent report showed that 5 mg folate/d raises serum folate concentrations 6–7 times and red blood cell folate concentrations 2 times com-pared with placebo (328). Diets high in folate have also been shown to raise serum folate concentrations up to 85% (329). One study suggests that increasing plasma folates in individuals above the third quartile of folate intake is not feasible. In a double-blind, placebo-controlled study of 82 alcoholic subjects receiving 1 mg/d for 18.5 d, it was found that whole-blood folate in these individu-als in the highest quartile of whole-blood folate (initially 3.73–7.70 nmol/g hemoglobin) could not be raised. However, sub-jects in the lowest 3 quartiles did show an increase with folate supplementation. The concentration in the lowest quartile (initially 0.71–2.06 nmol/g hemoglobin) was raised significantly by 0.8 nmol/g hemoglobin and the second lowest (initially 2.08–2.83 nmol/gm hemoglobin) by 0.75 nmol/g hemoglo-bin (330). It would be useful to test nonalcoholics as well (see the discussion of folate membrane transport above) and to measure tetrahydrofolate concentrations because alcohol interferes with folate absorption.

从补充剂和强化食品中摄取叶酸的UL,成人为1000克/天,2岁的为300克/天,16岁的儿童为800克/天。虽然在许多情况下似乎需要更高的数额。1例患者血清叶酸浓度为185 mg/L(正常浓度为6g/L)和红细胞叶酸浓度为591 mg/L(正常浓度:160克/升)4mo后添加12 mg叶酸/d。最近的一份报告显示,5毫克叶酸/日可使血清叶酸浓度提高6-7倍,红细胞叶酸浓度提高2倍,与安慰剂相比,可使血清叶酸浓度提高6-7倍。高叶酸水平的饮食也使血清叶酸浓度提高到85%。一项研究表明,在叶酸摄入量第三四分位以上的个体增加血浆叶酸是不可行的。在一项双盲安慰剂对照研究中,82名酒类受试者每天服用1mg/d,持续18.5天,结果发现,全血叶酸在全血叶酸的四分位数最高(最初为3.73-7.70nmol/g血红蛋白)不能提出。然而,在最低的3四分位数中,叶酸的添加量确实有所增加。最低四分位数的浓度(最初为0.71-2.06nmol/g血红蛋白)0.8nmol/g血红蛋白显著升高,0.75nmol/g血红蛋白升高幅度次之(最初为2.08~2.83 nmol/g血红蛋白)。因为酒精会干扰叶酸的吸收,所以也可以测试非酒精性的人(见上面关于叶酸膜转运的讨论)和测量四氢叶酸的浓度。古斯堪的那维亚语(Old Norse)

VITAMIN K 维生素K
The adequate intake of vitamin K is 90 g for women and120 g for men (8). The vitamin K–dependent proteins dis-cussed below are summarized in Table 10.

维生素K的适当摄入量女性为90克,男性为120克。表10概述了维生素K依赖蛋白.

γ-Glutamyl carboxylase: hemophilia γ-谷氨酰羧化酶:血友病
γ-Glutamyl carboxylase, with bound vitamin K in the presence of oxygen and carbon dioxide, converts glutamic acid residues to γ-carboxyglutamic acid residues on the amino-terminal regions of precursor forms of prothrombin (factor II) and factors VII, IX, and X (see OMIM 137167). These γ-carboxyglutamic acid residues are necessary for calcium-dependent phospholipid bind-ing by the vitamin K–dependent clotting factors and are prereq-uisites for normal blood coagulation (331).

谷氨酸羧化酶(γ-Glutamyl羧化酶)在氧气和二氧化碳存在下,结合维生素K,将谷氨酸残基转化为谷氨酸残基。γ-羧基谷氨酸残基位于凝血酶原(因子II)和因子VII、IX和X的氨基酸末端区域(见OMIM 137167)。这些,γ-羧基谷氨酸残基是钙依赖性磷脂与维生素K依赖的凝血因子结合所必需的,也是正常凝血的先决条件。

The binding sites for the γ-carboxylation recognition site con-taining propeptide and carboxylatable glutamate residues of a vitamin K–dependent substrate protein have been localized to the amino-terminal 250 residues of the enzyme. The carboxyl-terminal regions of the enzyme are important for conversion of vitamin K hydroquinone to vitamin K epoxide, a reaction that occurs concomitantly with carboxylation and is catalyzed by the vitamin K–dependent carboxylase. In addition, catalysis of vita-min K oxygenation by the enzyme is regulated by the availabil-ity of carboxylatable substrate (332).

含γ羧基化前肽的结合位点一种依赖于维生素K的底物蛋白的羧基谷氨酸残基已被定位于氨基末端250个酶的残基。该酶的羧基端区对维生素K对苯二酚转化为环氧维生素K具有重要意义,一种与羧化同时发生的反应,由维生素K依赖的羧化酶催化。此外,该酶对Vita-min K氧化的催化作用还受羧化底物的有效性调节。

The kinetic properties of a naturally occurring mutation in human -glutamyl carboxylase, Leu394→Arg, have been stud-ied (333). The mutant has a 5-fold higher Km (32.8 ± 5.4 mol/L) for vitamin K hydroquinone, the reduced form of vitamin K, than does the control (7.0 ± 1.2 mol/L). The coagulation activities of patients with combined deficiencies of vitamin K–dependent coagulation factors were partially corrected by the administration of vitamin K and vitamin K restored carboxylase activity from a low level to 33% of wild type (333). Thus, this seems to be a vitamin K–responsive Km mutant.

本文研究了人谷氨酰羧化酶(Leu 394→arg)自然突变的动力学性质。突变体对维生素K氢醌的Km(32.8±5.4mol/L)比对照高5倍(32.8±5.4mol/L)。联合缺乏维生素K依赖性凝血因子患者的凝血活性通过服用维生素K进行部分校正和维生素K使羧化酶活性从野生型的低水平恢复到33%。因此,这似乎是一个对维生素K敏感的KM突变体。

An infant girl with abnormal bleeding and some skeletal abnormalities who showed deficiency of vitamin K–dependent clotting factors II (8% of normal), VII (22%), IX (28%), and X (15%) was put on treatment consisting of intramuscular injec-tions of vitamin K and physiotherapy (331). After 7 d of treat-ment, the concentrations of factors II, VII, IX, and X rose to 60%, 65%, 112%, and 56% of controls, respectively. The patient was discharged with vitamin K injections (0.5 mg/kg body wt) every other day (later changed to 10 mg/d). Another patient with a Trp501→Ser mutation and deficiency of the same vitamin K– dependent factors was also responsive to vitamin K therapy (5 mg/d) and a binding defect was suspected: “the mutation may affect either the vitamin K-binding site or the propeptide-binding site” (334).

一名异常出血及部分骨骼异常的婴儿,显示缺乏维生素K-依赖凝血因子II(正常8%)、VII(22%)、IX(28%)和X(15%)被用于肌肉内损伤维生素K和理疗。治疗7d后,II、VII、IX、X因子浓度分别为对照组的60%、65%、112%和56%。患者每隔一天接受维生素K注射(0.5mg/kg体重)(后改为10 mg/d)。另一位患有Trp 501→Ser突变和缺乏相同的维生素K依赖因子的患者也对维生素K治疗(5mg/d)有反应,并怀疑存在结合缺陷:可能影响维生素K结合位点或前肽结合位点“

A patient congenitally deficient in factors II, VII, IX, and X was studied after a follow-up of 15 y (335). At birth, these fac-tors, when determined by clotting assays, were undetectable. After therapy with vitamin K1, the clotting activity of these fac-tors rose but never exceeded 18% of normal. Some molecules of the patient’s prothrombin lacked the normal complement of -carboxyglutamic acid residues. It was suspected that this rep-resents either a defective -carboxylation mechanism within the hepatocyte or faulty vitamin K transport; a Km mutation in -glutamyl carboxylase affecting vitamin K binding would be a plausible explanation. Vitamin K therapy could be tried in cases of inborn errors of blood clotting.

对一例先天缺乏因子II、VII、IX和X的患者进行了15岁随访研究。在出生时,当凝血试验确定这些因素时,是无法检测到的.维生素K1治疗后,这些因子的凝血活性提高,但从未超过正常值的18%。病人凝血酶原的一些分子缺乏正常的-羧基过剩氨基酸残留。有人怀疑这种代表对肝细胞内有缺陷的羧化机制或维生素K转运的缺陷感到不满;一个Km突变在,-谷氨酰羧化酶影响维生素K结合将是一个合理的解释。维生素K疗法可用于治疗先天凝血错误。

Propeptide of factor IX: hemophilia 因子Ⅸ前肽 :血友病

Blood clotting requires the posttranslational modification 凝血需要翻译后的修饰

(γ-carboxylation) and proteolysis of several blood clotting factors. The γ-carboxylation reaction is performed by γ-glutamyl carboxylase in the presence of vitamin K, carbon dioxide, and oxygen and precedes cleavage. A proteolysis cascade is required for clotting factor activation, in which the cleavage of each factor activates a proteolytic activity in the subse-quent protein so that the cascade can continue. The propeptide sequence of vitamin K–dependent proteins, such as factor IX propeptide, is a critical factor in the regulation of γ-carboxylation. One highly conserved residue of factor IX propeptide in par-ticular, the alanine at position 10 (A-10), seems to influence the carboxylation reaction. A patient was investigated that had a 6346G→A transition in genomic DNA, resulting in a muta-tion, A-10T, in the factor IX propeptide (336). The mutation resulted in the carboxylating enzyme, -glutamyl carboxy-lase, having a 33-fold increased Km for propeptide, as well as a less marked rise in Km of the enzyme-propeptide complex for vitamin K. The Km of the complex containing the wild-type propeptide was 4.2 mol/L, whereas the Km of the com-plex with the mutant A-10T propeptide for vitamin K was 9.3 mol/L and the Km of the complex with another mutant propeptide, A-10G, for vitamin K was 8.6 mol/L. These authors concluded, “Thus, both enzyme-peptide complexes containing variant peptides have lower affinities for vitamin K than the complex containing the wild-type peptide, but the dif-ference is not marked” (336). (See OMIM 306900.) It would be of interest to know whether patients would benefit from vitamin K therapy.

(γ-羧化)和几种凝血因子的蛋白水解:γ羧化反应是在维生素K、二氧化碳和氧气存在下,γ-谷氨酰基羧化酶发生裂解反应.凝血因子激活需要一个蛋白水解级联,在这个过程中,每一个因子的断裂都会激活亚硒蛋白中的一个蛋白水解活性,从而使级联能够继续下去。维生素K依赖蛋白的前肽序列,如第九因子,是调节γ羧化的关键因素。第九因子的一个高度保守的残基,即位于第10位(A-10)的丙氨酸,似乎影响了羧化反应。一名病人在基因组dna中进行了6346 G→A转换,导致第九因子前肽A-10T的突变。突变导致羧化酶,-谷氨酰羧酰化酶,前肽的Km增加33倍,此外,维生素K的酶原肽复合物的Km也没有明显增加。含有野生型前肽的复合物的Km为4.2mol/L,与突变型A-10T前肽的Km为9.3mol/L,Km为9.3mol/L。突变型前肽A-10G对维生素K的含量为8.6mol/L。这些作者得出结论:“因此,两种含有变异肽的酶肽复合物对维生素K的亲和力都比含有野生型肽的复合物低,但差异很大。无标记“(见OMIM 306900。)了解患者是否能从维生素K治疗中获益是很有兴趣的。

Tissue concentrations and toxicity 组织浓度和毒性

In vivo concentrations of vitamin K can be clinically manipu-lated (333). Plasma menaquinone-4 concentrations reached a maximum (a 10-fold increase) at 3 h after administration of 4 mg menaquinone-4 to 6 infants aged 5 d (337).

体内维生素K的浓度可以被临床应用。在注射4毫克甲喹酮-4至6名5天婴儿后3h,血浆脑膜喹酮-4浓度达到最大值(增加10倍)。

TABLE 9:Enzymes that use a folate cofactor or substrate1 使用叶酸辅助因子或底物的酶

Defective enzyme and EC no.
Localization
Reaction catalyzed
Disease or condition
OMIM no.
Inheritance
Methylenetetrahydrofolate reductase (NADPH) (1.5.1.20)
亚甲基四氢叶酸还原酶
Cytoplasmic
细胞质
5,10-Methylene-THF + NADPH → 5-methyl-THF + NADP
Homocystinuria, 高胱氨酸尿,vascular complications, 血管并发症,retardation发育迟缓,seizures癫痫,
psychiatric problems, 精神问题and neurologic abnormalities 神经异常(including schizophrenia, rages, and depression)包括精神分裂症,愤怒和抑郁
236250
Autosomal recessive
常染色体隐性
Methionine synthase (2.1.1.13)
]蛋氨酸合酶
Cytoplasmic 细胞质
Homocysteine + 5-methyl-THF →methionine + THF
Homocystinuria 高胱氨酸尿
156570
Autosomal recessive
Dihydrofolate reductase (1.5.1.3)
二氢叶酸还原酶
Cytoplasmic? 细胞质
Dihydrofolate + NADPH →tetrahydrofolate + NADP
Megaloblastic anemia 巨幼红胞性贫血and neurologic abnormalities神经异常
126060
Autosomal recessive
Glutamate formiminotransferase 谷氨酸亚胺甲基转移酶(2.1.2.5)
Cytoplasmic细胞质
THF + N-formimino-glutamate →5-formimino-THF + glutamate
Mental retardation智力迟钝
229100
Autosomal recessive
Folylpoly-γ-glutamate carboxypeptidase
(3.4.17.21)
Extracellular and lysosomal
[size=9.0000pt]
细胞外和溶酶体
Cleaves terminal glutamate off folylpoly--glutamates 末端谷氨酸从叶酸-谷氨酸中分离出来
Homocysteinemia
高半胱氨酸血症
600934
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1 OMIM, Online Mendelian Inheritance in Man (4); THF, tetrahydrofolate.

TABLE 10 Enzymes that use a vitamin K cofactor1 使用维生素K辅助因子的酶

Defective enzyme
Localization
Reaction catalyzed
Disease or condition
OMIM no.
Inheritance
γ-Glutamyl carboxylase[size=9.0000pt]
γ-谷氨酰羧化酶
Integral membrane protein
膜本体蛋白质
Glutamic acid of propeptide → -carboxyglutamic acid
[size=9.0000pt]
血友病 and
decreased γ-carboxyglutamate and clotting factorsγ-羧基谷氨酸与凝血因子
137167
Autosomal recessive
Propeptide of factor IX
因子Ⅸ前肽
Extracellular )细胞外
Glutamic acid of propeptide → γ-carboxyglutamic acid
Hemophilia
血友病
306900
X-linked
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CALCIFEROL (VITAMIN D) 骨化醇

The adequate intake of vitamin D (calciferol, or vitamin D3) is 5 g for middle-aged persons and 10 g for older persons (338). Two successive hydroxylations of vitamin D in the liver and kidney produce the hormonally active form, calcitriol (1,25-dihydroxyvitamin D3).

维生素D(钙素或维生素D 3)的适当摄入量中老年人为5克,老年人为10克。肝脏和肾脏中的维生素D连续两次羟化产生激素活性形式-钙基三醇(1,25-二羟基维生素D 3)。

Vitamin D receptor: vitamin D–dependent rickets II Calcitriol binds to the vitamin D receptor (see OMIM 601769),a nuclear transcription factor that regulates gene expression and is essential for the normal development of bone and the promo-tion of calcium transport across the small intestine. Defects in the vitamin D receptor lead to hypocalcemic vitamin D–dependent rickets, congenital total lipodystrophy, and persistent mullerian duct syndrome. The first known patient with a missense mutation in the vitamin D receptor hormone binding domain harbored a Arg271→Leu substitution and was not responsive to calcitriol (≤50 g/d), most likely because of a 1000-fold decreased affinity of vitamin D receptor for calcitriol in vitro (339).

维生素D受体:维生素D依赖性佝偻病Ⅱ钙三醇与维生素D受体结合(见OMIM 601769),调节基因表达的核转录因子和对于骨骼的正常发育是必不可少的和促进钙在小肠的转运。维生素D受体的缺陷导致维生素D依赖的佝偻病,先天性全脂营养不良,以及持续的毛拉管综合征。第一位在维生素D受体激素结合域发生错义突变的患者携带Arg 271→Leu替代物,对钙基三醇(≤50g/d)没有反应,很可能是因为维生素D受体在体外的亲和力降低了1000倍。

Other patients with missense mutations affecting calcitriol binding have, however, responded to high-dose vitamin D ther-apy (340–342). Sequence analysis of a hyporesponsive vitamin D receptor gene from one patient revealed a C-to-G transversion (His305→Gln) that caused an 8-fold decreased protein affinity for calcitriol (340). The patient was effectively treated with high doses (12.5 g/d) of calcitriol. Two other point mutations, Ile314→Ser and Arg391→Cys, have been found that confer reduced calcitriol-dependent activation of vitamin D receptor (341). Vitamin D receptor with the Arg391→Cys mutation was par-tially activated by high concentrations of hormone in vitro, which was reflected in the only partial responsiveness of the patient to calcitriol. On the other hand, vitamin D receptor activity of the Ile314→Ser mutant was more easily rescued by calcitriol, and the patient with this mutation was almost completely cured by calcitriol therapy. A similar patient (aged 18 mo) with a decreased affinity of vitamin D receptor for calcitriol responded well to administered hormone (20 g/d) with a resolution of serum calcium and phosphorous concentrations; marked clinical improvement, including the ability to stand and walk; and pro-gressive healing of the rickets (342).

其他有影响降钙素结合的错义突变的病人有,然而,对高剂量的维生素D治疗有反应。对一例患者维生素D受体基因的序列分析显示,C到G转换(His 305→Gln)使蛋白质对降钙素的亲和力降低了8倍。这位病人有效地接受了大剂量的治疗(12.5 g/d)的降钙素。另外两个点突变(ile 314→ser和arg 391→cys)被发现可以降低维生素D受体的钙基三醇依赖性激活。Arg 391→Cys突变的维生素D受体在体外被高浓度的激素激活,这反映在病人对降钙素唯一的部分反应。另一方面,Ile 314→Ser突变体的维生素D受体活性更容易被骨化三醇所挽救,并且该突变的患者经钙柠檬酸治疗几乎完全治愈。一名类似的患者(18岁),维生素D受体对钙基三醇的亲和力降低激素(20g/d)对血清钙磷浓度有较好的反应;显著的临床改善,包括站立和行走的能力,以及有利于佝偻病的治疗。

Three vitamin D receptor polymorphic alleles [polyA (long), BsmI (bb), and TaqI (TT)] were found in higher frequencies in colon cancer patients than in control subjects and were thus associated with an increased rate of cancer (343). Such reports rein-force the need to decipher genotype-phenotype relations, with the ultimate goal of catering medical interventions to the needs of individuals. If increased concentrations of calcitriol could overcome a protein defect associated with cancer, vitamin D therapy could be important for reducing cancer risk associated with such defects in the vitamin D receptor.

三种维生素D受体多态性等位基因 [polyA (long), BsmI (bb), and TaqI (TT)] 在结肠癌患者中发现的频率高于对照组,因此与癌症的发生率有关。这样的报道迫使我们必须破译基因型-表型关系,以满足个人需要的医疗干预为最终目标。如果增加钙基三醇的浓度可以克服与癌症相关的蛋白质缺陷,维生素D治疗对于减少与维生素D受体缺陷相关的癌症风险可能很重要。

In a study of the involvement of vitamin D deficiency (serum 25-hydroxyvitamin D3 < 50 nmol/L) in prostate cancer development, young men (40–51 y old) with low serum vitamin D con-centrations were at the greatest risk of developing prostate cancer (344). Cellular studies in prostate cancer cells suggested that vitamin D up-regulates androgen receptor expression, whereas androgens seem to up-regulate vitamin D receptor (344). If defects in vitamin D receptor (or androgen receptor) also predispose individuals to prostate cancer, such an activation of receptors by vitamin D administration seems like a possible protective measure for preventing against the onset of cancer in individuals (especially young men) with vitamin D receptor defects.

维生素D缺乏的相关性研究(血清25-羟维生素D 3<50 nmol/L)在前列腺癌的发展过程中,血清维生素D含量较低的年轻男性(40-51岁)患前列腺癌的风险最大。对前列腺癌细胞的细胞研究表明维生素D能上调雄激素受体的表达,而雄激素似乎能上调维生素D受体,如果维生素D受体(或雄激素受体) 的缺陷也会使人患前列腺癌,维生素D受体的激活似乎是预防维生素D患者(尤其是年轻男性)癌症的一种可能的保护措施。你知道吗?

By 1994, 50 cases of vitamin D receptor defects had been reported. Treatment is usually 20 g/d of the bioactive form, calcitriol, or 5 mg/d of the dietary form, vitamin D2, plus oral calcium and phosphate (345).Calciferol 1-hydroxylase: vitamin D–dependent rickets I The mitochondrial cytochrome P450c1gene codes for a cal-ciferol 1-hydroxylase (calcidiol 1-monoxygenase) that converts 25-hydroxyvitamin D3 to the hormone calcitriol. A genetic deficiency in the renal proximal tubules causes a pseudo–vitamin D–deficiency called rickets (see OMIM 264700). The P450c1 gene was analyzed in 19 individuals from 17 families representing various ethnic groups (346). All patients had P450c1 mutations on both alleles. In the French Canadian population, among whom vitamin D–dependent rickets I is common, 9 of 10 alleles bore the haplotype 4-7-1 and carried the mutation 958G. Patients are treated with a physiologic dose of calcitriol; thus, the hormone is replaced, but the remediation does not appear related to a change in Km.

到1994年,报告了50例维生素D受体缺陷。治疗通常是20克/天的生物活性形式,钙三醇,或饮食形式的5毫克/天,维生素D 2,加上口服钙和磷酸盐。沉钙固醇1-羟化酶:维生素D:依赖性佝偻病Ⅰ线粒体细胞色素P450c1沉钙固醇1-羟化酶:维生素D基因编码它将25-羟基维生素D 3转化为降钙素。肾近端小管遗传缺陷导致假性-维生素D缺乏称为佝偻病(见OMIM 264700)。对来自不同民族的17个家系的19名个体进行了p450c1基因分析。两种等位基因均有P450c1突变。在加拿大的法裔人口中,其中维生素D依赖型佝偻病我很常见,10个等位基因中有9个携带单倍型4-7-1,并携带958G突变。患者接受生理剂量的降钙素治疗,因此,激素被替代,但补救措施似乎与Km的变化无关。

Morphea:硬斑病

Morphea is a skin-associated scleroderma, a disease of the connective tissue involving increased collagen synthesis and deposition in various organs and skin. A significant clinical improvement was observed in 3 patients with generalized morphea who were given 0.50–0.75 g calcitriol/d (347). If the mechanism of action—possibly immunoregulatory or growth inhibitory—involved altered binding for the vitamin hormone, then it seems plausible that remediation of scleroderma or morphea with vitamin D results from raising the rate of some reaction in that pathway.

摩洛哥是一种皮肤相关的硬皮病,结缔组织的一种疾病,包括在各种器官和皮肤中增加胶原合成和沉积。3例全身性睡眠期患者给予0.50-0.75克降钙素/d,临床疗效明显改善。如果作用机制-可能是免疫调节或生长抑制-改变了与维生素的结合,因此,用维生素D治疗硬皮病或摩洛哥似乎是因为提高了该途径中某些反应的速率。

Tissue concentrations and toxicity 组织浓度和毒性

Data accumulated in the DRI manual suggest a direct relation between vitamin D intake and 25-hydroxyvitamin D concentrations. The UL of dietary vitamin D is 50 g/d and adverse effects have been seen at concentrations ranging from 250 to 1250 g/d (338).
DRI手册中积累的数据表明维生素D摄入量与25-羟基维生素D浓度之间存在直接关系。膳食维生素D的UL为50 g/d,在250~1250 g/d的浓度范围内出现了不良反应。

TOCOPHEROL  (VITAMIN E) 生育酚 维生素E
α-Tocopherol is the main form of the lipid-soluble vitamin E α-生育酚是脂溶性维生素E的主要形式。

in animal tissues and plasma. The DRI for vitamin E is 15 mg/d (  1.5 IU/mg = 22.5 IU/d) as -tocopherol (348).
在动物组织和血浆中。维生素E的DRI为15 mg/d(1.5 IU/mg=22.5 IU/d)As-生育酚

α-Tocopherol transfer protein: ataxia with isolated vitamin E deficiency α-生育酚转运蛋白:单纯性维生素E缺乏症共济失调

With structural similarity to other lipophilic vitamin bind-ing proteins, α-tocopherol transfer protein (TTP), present in the liver and cerebellum, is responsible for the incorporation of α-tocopherol into lipoproteins and for the transport of α-tocopherol between membranes. An autosomal recessive dis-ease characterized by ataxia with isolated vitamin E deficiency (AVED, see OMIM 277460) is caused by mutations in TTP. Patients with AVED retain normal intestinal absorption of vitamin E, but have defective incorporation of vitamin E into VLDLs by hepatic cells. The disease involves abnormally low serum concentrations of α-tocopherol, absent tendon reflexes, cardiomyopathy, and intel-lectual decline. The prevention of neuronal damage associated with AVED is typically mediated by lifelong supplementation with high doses of vitamin E (800 mg/d), and other symptoms can be averted if therapy is started early enough.

与其他亲脂维生素结合蛋白结构相似,α-生育酚转运蛋白(TTP),存在于肝脏和小脑,负责α-生育酚与脂蛋白的结合以及α-生育酚在膜间的转运。一种具有分离维生素E缺陷性共济失调的常染色体隐性不容易性(艾维德,见OMIM 277460)是由TTP突变引起的。患者肠内维生素E吸收正常,但有缺陷的维生素E掺入到VLDLs肝细胞。这种疾病包括血清α-生育酚浓度异常低,肌腱反射缺失,心肌病和智力下降。预防AVED相关的神经元损伤通常是通过终生补充高剂量维生素E(800 mg/d)来实现的,如果开始治疗,其他症状可以避免。够早的了。

In 3 individuals, vitamin E responsiveness was attributed to mutations in the gene encoding TTP (349). Two siblings were com-pound heterozygotes for a 421G→A transition (Glu141→Lys) and a 513-514 TT insertion. A third case from another family was homozygous for a 552G→A splice site mutation. Serum α-tocopherol concentrations dropped below normal with treatment withdrawal, confirming the impaired ability of AVED patients to conserve α-tocopherol in the body. Serum α-tocopherol concentrations were raised when treatment was reinstated.

在3个个体中,维生素E反应性是由编码TTP的基因突变引起的。两个兄弟姐妹分别为421 G→A转换(Glu141TT Lys)和513-514TT插入的COM-磅杂合子。另一个家系的第三个病例是552 G→A剪接位点突变的纯合子。停药后血清α-生育酚浓度降至正常水平,证实α患者体内保存α-生育酚的能力受损。恢复治疗后血清α-生育酚浓度升高。

The effectiveness of high-dose vitamin E treatment (800 mg/d) for 1 y was quantitatively measured in 24 AVED patients with use of the ataxia rating scale (350). All participants had the 744delA mutation in TTP, which is common to AVED patients in Tunisia. Mean scores on the ataxia rating scale decreased from 45 to 35 over the year, with statistically significant incremental drops at 3, 6, 9, and 12 mo. Serum vitamin E concentrations normalized as well.

应用共济失调评定量表,定量测定了24例老年痴呆患者服用高剂量维生素E(800 mg/d)治疗1y的疗效。所有参与者都在TTP中发生了744DELA突变,这对于突尼斯的Ave患者是常见的。共济失调评分量表的平均评分从45岁下降到35岁,在3,6,9和12 mo时,有统计学意义的递增下降。血清维生素E浓度也已正常化。

The success of vitamin E may be attributed to either the nonenzymatic saturation of serum or the saturation of the hepatic TTP enzymes so as to accelerate vitamin E incorporation into VLDL. The latter scenario would likely entail the overcoming of an altered binding of TTP with vitamin E.

维生素E的成功可归因于血清非酶饱和或肝TTP酶的饱和,从而加速维生素E掺入VLDL。后一种情况可能需要克服TTP与维生素E的结合改变。

Tissue concentrations and toxicity 组织浓度和毒性

The UL of vitamin E on the basis of supplementation with α-tocopherol is 1000 mg/d (1500 IU) as a result of adverse effects including increased risk of hemorrhage (348). In 2 patients mentioned above, the reinstatement of α-tocopherol treatment showed a linear relation to serum α-tocopherol concentrations. The maximal dosage (40 mg · kg body wt1 · d1) resulted in a plasma concentration > 50 mol/L (349).

在补充α-生育酚的基础上,维生素E的UL为1000 mg/d(1500 IU),这是由于不良反应(包括增加出血风险)造成的。在上述2例患者中,α-生育酚治疗的恢复与血清α-生育酚浓度呈线性关系.最大剂量(40 mg·kg体重WT1·D1)导致血浆浓度>50 mol/L。

TETRAHYDROBIOPTERIN 四氢生物蝶呤

No DRI has been set for tetrahydrobiopterin. 未对四氢生物蝶呤进行DRI。

Phenylalanine hydroxylase: phenylketonuria II (mild hyperphenylalaninemia)

苯丙氨酸羟化酶:苯丙酮尿症II(轻度高苯丙氨酸血症)

Phenylalanine hydroxylase (PAH; phenylalanine 4-monoxyge-nase), the enzyme responsible for classic phenylketonuria (OMIM 261600), utilizes tetrahydrobiopterin to convert pheny-lalanine into tyrosine, a critical step in dopamine biosynthesis. Defects in PAH often lead to mental retardation as a result of the accumulation of phenylalanine and its neurotoxic metabolites.

苯丙氨酸羟化酶 (PAH; phenylalanine 4-monoxyge-nase),引起经典苯丙酮尿症的酶(OMIM 261600),利用四氢生物蝶呤将苯丙氨酸转化为酪氨酸,这是多巴胺生物合成的关键步骤。PAH的缺陷往往导致精神发育迟缓,这是由于苯丙氨酸及其神经毒性代谢产物的积累所致。

Four patients with mild hyperphenylalaninemia (sometimes termed nonphenylketonuria hyperphenylalaninemia) responded to tetrahydrobiopterin therapy (5 or 10 mg/kg body wt) with a decrease in elevated serum phenylalanine concentrations (253). Because there were no abnormalities in urinary pteridine or DHPR activity, and mutations were detected in the PAH gene, it was presumed that these cases reflected a novel subtype of PAH deficiency responsive to cofactor supplementation. The authors suggested that the mutants “probably form mutant PAH with a high Michaelis-Menten constant Km for tetrahydrobiopterin. It is likely that [tetrahydrobiopterin] supplementation increased the intracellular [tetrahydrobiopterin] concentration to restore residual PAH activity and/or to stabilize the mutant PAH molecules” (253). The patients’ protein defects were characterized in a screen of mutations typical of classic phenylketonuria. The patients, who were all compound heterozygotes, harbored mutations in PAH that are present in classic phenylketonuria. Other similar reports of successful tetrahydrobiopterin treatment support the view that tetrahydrobiopterin therapy is effective in some PAH-deficient patients because of Km variants of the enzyme (351, 352). A 60-mg dose of tetrahydrobiopterin (20 mg/kg) was used to significantly decrease blood phenylala-nine in one of the patients, who was continued on 45 mg/d (352).

轻度高苯丙氨酸血症4例(有时称为非苯丙酮尿症、高苯丙氨酸血症)四氢生物蝶呤治疗(5或10 mg/kg体重)可降低血清苯丙氨酸浓度。因为没有异常的尿蝶啶或DHPR活性,在PAH基因中检测到突变,推测这些病例反映了一种新的PAH缺乏症亚型。作者提出该突变体“很可能形成突变的PAH,具有高度的米氏-梅内顿常数Km,用于四氢生物蛋白。[四氢生物蝶呤]的补充很可能增加细胞内[四氢生物蝶呤]浓度,以恢复残留的PAH活性和/或稳定突变的PAH分子。患者的蛋白质缺陷的特征是一个典型的典型苯丙酮尿症突变筛查。这些病人都是复合杂合子,在经典苯丙酮尿症中存在的PAH中的钻孔突变。其他成功的四氢生物蝶呤治疗成功的报告也支持这样的观点,即四氢生物蝶呤治疗部分PAH缺乏的患者是有效的,因为该酶的km变体。其中一名患者服用60毫克四氢生物蝶呤(20毫克/公斤),可显著降低血苯拉拉-9,持续45毫克/天。

In Portugal, the third most common mutation in the PAH gene (8.9% of mutant alleles), Val388→Met, has a reduced enzymatic activity and a 3.7-fold increased Km for tetrahydrobiopterin (82 mol/L) as compared with the wild type (22 mol/L) (353). Although the mutation does not seem to reside in the putative pterin binding motif, it does affect cofactor binding and thus may prove to be another tetrahydrobiopterin-remediable form.

在葡萄牙,PAH基因第三常见突变(8.9%的突变等位基因),Val388→Met,与野生型(22 mol/L)相比,四氢生物蝶呤(82 mol/L)的酶活性降低,Km增加3.7倍。虽然这种突变似乎并不存在于推测的翼龙结合基序中,它确实影响辅助因子结合,因此可能被证明是另一种四氢生物蝶呤-可补救的形式。

A recent review (354) evaluated the 3 reports of tetrahydro-biopterin-responsiveness to date (253, 352, 355) and stated that tetrahydrobiopterin therapy is effective in some PAH-deficient patients because the primary defects affect cofactor binding. In fact, several of the PAH mutations in tetrahydrobiopterin-responsive individuals have been assigned to regions of cofactor interaction (354). It remains to be seen, however, what percent-age of hyperphenylalaninemias are due to tetrahydrobiopterin-responsive variants of PAH. We suggest that tetrahydrobiopterin therapy be considered with any case of phenylketonuria that might not be a classic case. The PAH Mutation Analysis Con-sortium Database contains information on the hundreds of mutations found in PAH (356).

最近的一次审查评估了迄今为止有关四氢生物蝶呤的3份报告(253, 352, 355)并指出四氢生物蝶呤治疗部分PAH缺乏的患者是有效的,因为原发性缺陷影响辅助因子结合。事实上,对四氢生物蝶呤有反应的个体中的几个PAH突变已经被分配到辅助因子相互作用的区域。然而,由于四氢生物蝶呤反应变异的PAH,高苯丙氨酸血症的年龄是多少还有待观察.我们建议用四氢生物蝶呤治疗任何可能不是典型病例的苯丙酮尿症。PAH突变分析Con-sortium数据库包含了在PAH中发现的数百个突变的信息。

S-ADENOSYLMETHIONINE S-腺苷甲硫氨酸

No DRI has been set for S-adenosylmethionine.未对S-腺苷甲硫氨酸进行DRI测定.

Guanidinoacetate N-methyltransferase 胍基乙酸-N-甲基转移酶

[size=9.0000pt]S-Adenosylmethionine, a common methyl donor, is used by guanidinoacetate N-methyltransferase (see OMIM 601240), which catalyzes the last step in creatine synthesis, the methylation of guanidoacetate to creatine. Guanidinoacetate N-methyltransferase deficiency is a rare inborn error of metabolism that leads to creatine deficiency. Creatine administration, which bypasses the metabolic defect, alleviates symptoms of guanidinoacetate N-methyltransferase deficiency (357). Because the concentration of guanidoacetate, which has neurotoxic effects, remains high after creatine supplementation, S-adenosylmethionine administration could be of additional benefit. It would also be useful to elucidate the primary defect of the guanidinoacetate N-methyltransferase protein.

T-腺苷甲硫氨酸,一种普遍的甲基供体,是由胍基乙酸N-甲基转移酶催化的,催化肌酸合成的最后一步,即胍乙酸甲酯甲基化生成肌酸。胍基乙酸N-甲基转移酶缺陷,是一种罕见的先天代谢错误,导致肌酸缺乏。肌酸钠绕过代谢缺陷,减轻胍基乙酸N-甲基转移酶缺乏症。由于具有神经毒性作用的胍乙酸酯浓度在补充肌酸后仍然很高,SAMe给药可以具有额外的益处.这也有助于阐明胍基乙酸N-甲基转移酶蛋白的主要缺陷。

PANTOTHENIC ACID 泛酸
The DRI for pantothenic acid, the nutritional precursor of coenzyme A, is 5 mg/d for adults (7). 辅酶A的营养前体泛酸的DRI为成人每日5 mg/d

3-Methylglutaconic aciduria and cardiomyopathy 3-甲基谷氨酸尿与心肌病

4-Methylglutaconate is an intermediate in the catabolism of leucine, but whereas the primary metabolic defect in type I 3-methylglutaconic aciduria has been described (namely, methylglutaconyl-CoA hydratase deficiency), no specific defect in the type II presentation has as yet been identified (see OMIM 302060).
3-甲基谷氨酸是亮氨酸分解代谢的中间产物,然而,对于Ⅰ型3-甲基谷氨酸尿的原发性代谢缺陷却有描述(即甲基谷氨酸-辅酶A水合酶缺乏症),到目前为止,还没有发现II型表现的具体缺陷(见OMIM 302060)。

In one case report, a young boy presented with dilated cardiomyopathy, growth failure, neutropenia, low serum cholesterol, and increased urinary excretion of 3-methylglutaconic and 3-methylglutaric acids (358). At a point when the patient was moribund, large doses of pantothenic acid, a precursor of coenzyme A, produced a dramatic and sustained improvement in myocardial function, growth, neutrophil cell count, hypocholes-terolemia, and hyperuricemia, which suggested that a limitation in the availability of coenzyme A was the fundamental patho-logic process in this condition. The dose of pantothenate was increased from 15 mg/d at the beginning to 3   50 mg/d. It is unclear why the patient responded to pantothenate, but it is possible that he had a defect in a CoA-metabolizing enzyme such as pantothenic acid kinase.

在一个案例中,一个小男孩患有扩张型心肌病,生长衰竭,中性粒细胞减少,3-甲基谷胱甘肽和3-甲基戊二酸的低血清胆固醇和尿排泄增加。在患者濒死的时刻,大剂量的泛酸,辅酶A的前体,使心肌功能有了显著的持续改善,生长、中性粒细胞计数、低胆固醇血症和高尿酸血症,说明在这种条件下,辅酶A的有效性受到限制是最基本的病理过程。泛酸剂量从开始时的15 mg/d增加到3 50 mg/d。目前还不清楚为什么病人对泛雌生殖有反应,但这可能是他有缺陷,在辅酶代谢酶,如泛酸激酶。

In a study of 25 mothers of children with birth defects (psychomotor retardation of unknown cause and microcephaly), 6 were found to excrete large amounts of 3-methylglutaconic acid (16 times that of control subjects) and 3-methylglutaric acid (6 times that of control subjects) (359). It is thus possible that feeding pantothenic acid to women with high concentrations of 3-methylglutaconic and 3-methylglutaric acid might lower the excretion rate of the 2 acids, normalize metabolism, and prevent future birth defects.

25名新生儿出生缺陷母亲的研究(不明原因的精神运动性迟滞和小头畸形),发现6种物质可分泌大量3-甲基谷氨酸(是对照组的16倍)和3-甲基戊二酸(对照受试者的6倍)。因此,向高浓度3-甲基谷氨酰胺的妇女喂食泛酸是可能的和3-甲基戊二酸可降低2种酸的排泄率,使代谢正常,防止将来的出生缺陷。

Pantothenate kinase: Hallervorden-Spatz syndrome and pantothenate kinase–associated neurodegeneration

泛酸激酶:哈弗拉尔沃登-斯帕兹综合征和泛酸激酶相关神经变性

Pantothenate kinase is a cytosolic enzyme responsible for the first step in the biosynthesis of CoA from pantothenic acid (vitamin B5). Four genes encoding pantothenate kinase have been identified: PANK1 (expressed in heart, liver, kidney), PANK2 (ubiquitous), PANK3 (predominantly liver), and PANK4 (ubiqui-tous, predominantly muscle). Mutations in PANK2, which is the most abundantly expressed form in the brain, were recently impli-cated in pantothenate kinase–associated neurodegeneration (see OMIM 234200), an autosomal recessive neurodegenerative disorder characterized clinically by dystonia and often optic atrophy or pigmentary retinopathy and biochemically by iron deposits in the basal ganglia and globus pallidus (360). The mutations identified in PANK2 fall into exons 1C, 2, 3, 4, 5, and 6. Missense mutations resulting in nonconservative amino acid changes were found in 32 of 38 classical pantothenate kinase–associated neurodegener-ation cases. All 17 mutations found in atypical cases were mis-sense mutations. It seems plausible that some of these mutations will lower pantothenate kinase activity by affecting the affinity of the enzyme for pantothenate substrate. Such cases may prove to be responsive to high-pantothenate therapy.

泛酸激酶是由泛酸(VitB 5)合成辅酶A的第一步,是一种胞浆酶。已鉴定出四个编码泛酸激酶的基因:PANK 1(表达于心脏、肝脏、肾脏)、PANK 2(普遍存在)、PANK 3(以肝脏为主)和PANK 4(以肌肉为主)。PANK 2基因突变,它是大脑中最丰富的表达形式,最近在泛酸激酶相关神经变性中被植入(见OMIM 234200),以肌张力障碍为特征的常染色体隐性神经退行性疾病化热视神经萎缩或色素性视网膜病变化热以及基底节区和苍白球区的铁沉积。PANK 2的突变属于外显子1C、2、3、4、5和6。38例经典泛酸激酶相关神经退行性变病例中,32例出现错义突变,导致非保守性氨基酸改变。在非典型病例中发现的所有17种突变均为错义突变。似乎有可能的是,这些突变中的一些将降低泛酸激酶的活性,通过影响酶与泛酸底物的亲和力。这种情况可能被证明是对高泛酸盐疗法的反应。

Tissue concentrations and toxicity 组织浓度和毒性

No UL for pantothenic acid has been established because there have been no reports of adverse affects (7).没有建立泛酸的UL,因为没有任何不良影响的报告。

LIPOIC ACID 硫辛酸
No DRI has been set for lipoic acid. 没有DRI已设置硫辛酸。
二氢硫辛酰胺脱氢酶: lactic acidosis, cerebral cortical atrophy, and hearing loss 乳酸酸中毒、大脑皮层萎缩和听力损失

Deficiency of dihydrolipoamide dehydrogenase, the E3 component of all 3 mitochondrial α-ketodehydrogenase complexes (pyruvate, α-ketoglutarate, and branched-chain α-ketoacid), results in decreased activity of the dehydrogenases and lactic acidosis (OMIM 246900). Lipoic acid is covalently linked to a lysine residue in PDHC, KGDH, and BCKAD (see the section on thiamine).

二氢硫辛酰胺脱氢酶缺乏症,3种线粒体α-酮脱氢酶复合物的E3组分(丙酮酸,α-酮戊二酸,和支链α-酮酸),脱氢酶活性降低与乳酸酸中毒 (OMIM 246900).硫辛酸与PDHC、KGDH和BCKAD中的赖氨酸残基共价连接(见关于硫胺素的一节)。

An 8-mo-old boy with severe lactic acidosis was found to have dihydrolipoamide dehydrogenase deficiency (361). Dihy-drolipoamide dehydrogenase activity in the patient’s fibroblasts was reduced to 20% of the control and kinetic studies found an increased Km for NAD and NADH (382 and 83 mol/L, respec-tively) in the patient compared with control subjects (201 and 56 mol/L, respectively). No significant differences in the Km for lipoamide were found between control subjects and the patient, although this measurement was not definitive. Acidosis could not be relieved by thiamine, biotin, bicarbonate, protein restriction, or a ketogenic diet. Oral administration of lipoic acid (25–50 mg/kg) produced marked improvements in lactic and pyruvic acidemia, and the child continued to do well 2 y later, with clinical improvements.

一名患有严重乳酸酸中毒的8岁男童被发现患有二氢硫磷酰胺脱氢酶缺乏症。二氧磷酰胺脱氢酶活性在患者成纤维细胞中降低到对照组的20%,动力学研究发现NAD的Km增加和NADH分别为382和83 mol/L,对照组分别为201和56 mol/L。 在正常人和病人之间,对硫辛胺的知识管理没有明显的差异,尽管这个测量不是确定的。硫胺素、生物素、碳酸氢钠、蛋白质限制或生酮饮食不能缓解酸中毒。口服硫辛酸(25-50毫克/千克)可显著改善乳酸和丙酮酸血症,两年后,随着临床的改善,孩子继续做得很好。

Two other patients with Friedreich ataxia and dihydrolipoamide dehydrogenase deficiency had an 4-fold increased Km for both lipoamide substrate and NAD cofactor (362). It is unclear how the patients were treated. Future patients with a high Km for NAD may benefit from high-dose niacin treatment; physicians should consider riboflavin treatment as well because the lesion in at least one case of dihydrolipoamide dehydrogenase deficiency was a 3–base pair deletion in the FAD cofactor binding region of E3 (363).

另外两例弗里德里希共济失调和二氢硫辛酰胺脱氢酶缺乏症患者的脂酰胺底物和NAD辅助因子的Km都增加了4倍。目前尚不清楚这些病人是如何治疗的。未来高Km NAD患者可能受益于大剂量烟酸治疗;医生也应该考虑核黄素的治疗,因为至少一例二氢硫辛酰胺脱氢酶缺乏症的病灶是E3中fad辅助因子结合区3碱基对的缺失。

In a case of lipoate-responsive pyruvate dehydrogenase deficiency, PDHC and E1 activities were severely depressed in the patient. Lactate homeostasis responded to pharmaco-logic supplements of lipoic acid, but the child died at the age of 20 mo (364).

在一例硫辛酸反应的丙酮酸脱氢酶缺乏症中,PDHC和E1活性在患者中受到严重抑制。乳酸稳态对硫辛酸的药效学补充剂起作用,但该儿童在20岁时死亡。

CARNITINE 肉(毒)碱
No DRI has been set for carnitine. 卡尼汀没有被设定为DRI。

Carnitine O-acyltransferase: fatty acid toxicity 肉毒碱O-酰基转移酶:脂肪酸毒性

Carnitine O-acyltransferase is responsible for transporting fatty acids into the mitochondria. An infant girl with defective carnitine O-acyltransferase died at 31 h of age with profound macrovesicu-lar fatty infiltration of liver, kidney, and muscle found on postmortem examination, suggestive of a defect in fatty acid -oxidation (365). Carnitine was not fed because the defect was found only on autopsy; thus, it is unclear whether the enzyme had a Km defect remediable by carnitine feeding, but it seems likely that other altered enzymes will. With age, carnitine O-acyltransferase activity decreases and the Km of carnitine O-acyltransferase for both carnitine and CoA increase in rat brain. Additionally, carni-tine supplementation restores activity (17).

肉碱O-酰基转移酶负责将脂肪酸转运到线粒体.一名患有肉碱O-酰基转移酶缺陷的女婴于31小时死亡,在尸检中发现的肾脏和肌肉,肝脏脂肪浸润严重,提示脂肪酸氧化存在缺陷。肉毒碱不喂食,因为只有在尸检时才能发现肉毒碱的缺陷;因此,目前还不清楚该酶是否有Km缺陷,可通过肉碱喂养,但似乎其他改变的酶会。随着年龄的增长,大鼠脑内肉碱O-酰基转移酶活性降低,肉碱O-酰基转移酶的Km增加。此外,补充剂还能恢复活动。

Carnitine transporter 肉碱转运体
Primary systemic carnitine deficiency is due to a defect in the specific high-affinity carnitine transporter, which is expressed in most tissues and is responsible for bringing carnitine into the cytosol. This carnitine uptake defect, which is characterized by progressive infantile-onset carnitine-responsive cardiomyopathy, weakness, recurrent hypoglycemic hypoketotic encephalopathy, and failure to thrive, was identified in 2 unrelated patients (366). Each patient was a compound heterozygote with both alleles mutated by deletions and insertions and responded dramatically to high-dose carnitine supplementation. A low-affinity, high-concentration, nonspecific-diffusion uptake of carnitine into the cells was sus-pected, which bypassed the specific carrier-mediated transporter. Although these particular carnitine-responsive mutations were not likely to have affected the Km, other mutations could.

原发性系统性肉碱缺乏是由于特殊的高亲和力肉碱转运体的缺陷,它在大多数组织中都有表达,并负责将肉碱带入胞浆。这种肉碱摄取缺陷,其特征是进行性婴儿发作的肉碱反应型心肌病,虚弱,复发性低血糖性脑病,在两个不相关的病人中,我们发现了失败的原因。每个病人都是一个复合杂合子,两种等位基因都通过缺失和插入而发生突变,并对大剂量肉碱的补充产生了显著的反应。将肉碱低亲和力、高浓度、非特异性扩散吸收到细胞内,绕过载体介导的转运体.虽然这些特殊的肉碱反应突变不太可能影响KM,但其他突变可能会影响KM。


HORMONES, AMINO ACIDS, AND METALS 激素、氨基酸和金属
There is evidence that some diseases and conditions may be associated with an altered metabolism or altered binding of amino acids, metals, and hormones. The following examples are not necessarily conclusive Km remediable defects, but rather evi-dence of the wide array of genetic profiles and conditions that may fit the nutrient-remediable mold.

有证据表明,某些疾病和疾病可能与代谢改变或氨基酸、金属和激素结合改变有关。以下例子不一定是结论性的KM可补救的缺陷,而是广泛的基因图谱以及符合营养治疗可能补剂的条件。

Thyroid hormone: neurologic defects 甲状腺激素:神经系统缺陷

Similar to the case with the vitamin D receptor (see the sec-tion on calciferol), mutations have been found in the thyroid hor-mone receptor β (see OMIM 190160) that affect the affinity for hormone ligand. Such mutations lead to increased circulating concentrations of thyroid hormone with normal or elevated con-centrations of thyroid-stimulating hormone in serum and defects in growth and neurologic development. One child with a Pro453→Thr missense mutation had significantly reduced tri-iodothyronine binding affinity and was treated successfully with triiodothyroacetic acid (367). This therapy has been successful in ≥ 8 other patients (368) and a 1994 review found 26 mutations localized to the hormone binding domain of the thyroid hormone receptor β  (369). The ability of in vitro synthesized mutant pro-teins to bind triiodothyronine was moderately or markedly reduced and the ability to activate or repress target gene expres-sion was impaired. A missense mutation found in affected het-erozygotes of one family caused a 12-fold decreased affinity of receptor for ligand (370). The evidence suggests that a Km muta-tion in the thyroid hormone receptor β  gene may be overcome by administration of triiodothyroacetic acid. The thyroid hormone receptor β  system may serve as a model for receptor mutations for other hormones.

类似于维生素D受体,甲状腺激素受体β已发现突变,影响对激素配体的亲和力。这种突变会导致血清中甲状腺刺激素浓度正常或升高的情况下循环中甲状腺激素浓度的增加而生长和神经发育的缺陷。一名患有Pro453→Thr错义突变的儿童用三碘甲状腺乙酸成功治疗三碘甲腺原氨酸结合亲和性并成功治疗。在其他8例患者中,这种疗法已成功。1994年的一次审查发现26个位于甲状腺激素受体β的激素结合区的突变。体外合成的突变体脯氨酸结合三碘甲状腺原氨酸的能力中度或明显降低即激活或抑制靶基因表达的能力受到损害。在一个家族的受精卵中发现一个错义突变,导致受体与配体亲和力降低12倍。提示甲状腺激素受体β基因的Km突变可被三碘甲状腺乙酸所克服。甲状腺激素受体β系统可作为其他激素受体突变的模型。

Alanine and isoleucine: Huntington disease 丙氨酸和异亮氨酸:亨廷顿病

Alanine and isoleucine were found to be significantly lower in the plasma and cerebrospinal fluid of 16 Huntington disease patients than in that of 21 age-matched control subjects (371). It was hypothesized that defects in cellular uptake or metabolism of neutral amino acids could be a consistent feature of Hunting-ton disease. This suggests treatment with alanine and isoleucine if the defect is in transport and pyridoxine if the defect is in transamination.
16例亨廷顿病患者血浆和脑脊液中丙氨酸和异亮氨酸明显低于21例年龄匹配的对照组。假设中性氨基酸的细胞摄取或代谢中的缺陷可能是狩猎-吨疾病的一致特征。这建议用丙氨酸和异亮氨酸治疗,如果缺陷是在运输中,而吡多辛,如果缺陷是在转运。

Serine and glycine: 3-phosphoglycerate dehydrogenase deficiency, seizures, and microcephaly
丝氨酸和甘氨酸:3-磷酸甘油酸脱氢酶缺乏症 ,癫痫和小头畸形

3-Phosphoglycerate dehydrogenase deficiency (OMIM 601815) is an inborn error of serine biosynthesis. Patients are affected with con-genital microcephaly, psychomotor retardation, and intractable seizures. In 2 siblings studied, L-serine of ≤500 mg·kg1 ·d1 was not sufficient for seizure control (49). Addition of 200 mg glycine·kg1 ·d1 resulted in the complete disappearance of seizures, however, and electroencephalographic abnormalities grad-ually resolved after 6 mo. Biochemical abnormalities in this disor-der are found in the fasted state and consist of low concentrations of the amino acids serine and glycine in plasma and cerebrospinal fluid (49). This appears to be a replacement therapy for a deficiency of serine biosynthesis; thus, a Km defect in 3-phosphoglycerate dehydrogenase seems unlikely, but further mechanistic work needs to be done. Clinicians should use caution, however, because higher doses of serine (1400 mg·kg1 ·d1 ) have caused adverse effects (50).

3-磷酸甘油酸脱氢酶 (OMIM 601815)是丝氨酸生物合成的先天错误。患者患有先天性小头畸形、精神运动性迟滞和顽固性癫痫.在研究的两个兄弟姐妹中,≤500 mg·kg1·d1的L-丝氨酸不足以控制癫痫发作。添加200 mg甘氨酸·Kg1·D1可使癫痫完全消失,脑电图异常在6mo后逐渐消失。这种病的生化异常存在于禁食状态,包括血浆和脑脊液中低浓度的氨基酸丝氨酸和甘氨酸。这似乎是一种替代治疗丝氨酸生物合成不足;因此,3-磷酸甘油酸脱氢酶的Km缺陷似乎不太可能,但还需要进一步的机械工作。然而,临床医生应该谨慎,因为更高剂量的丝氨酸(1400 mg·Kg1·D1)已引起不良反应

Zinc: familial amyotrophic lateral sclerosis and Alzheimer disease 锌: 家族性肌萎缩侧索硬化症与阿尔茨海默病

Mutations in Cu/Zn superoxide dismutase (see OMIM 147450) cause 25% of familial amyotrophic lateral sclerosis. Several of the Cu/Zn superoxide dismutase mutants involved with familial amyotrophic lateral sclerosis have been found to have a decreased affinity for zinc (372, 373), up to 30-fold in some mutants (374). The loss of zinc from wild-type super-oxide dismutase approximately doubles the efficiency of the enzyme for catalyzing peroxynitrite-mediated tyrosine nitra-tion, suggesting that this gained function by superoxide dis-mutase in amyotrophic lateral sclerosis may be an indirect consequence of zinc loss. Nitration of protein-bound tyrosines is a permanent modification that can adversely affect protein function. Thus, the toxicity of superoxide dismutase mutants associated with amyotrophic lateral sclerosis may be related to enhanced catalysis of protein nitration subsequent to zinc loss (374). In a recent study, both wild-type and amyotrophic lateral sclerosis mutant superoxide dismutase protected motor neurons when replete with both copper and zinc. When the same proteins were made zinc deficient, all initiated apoptosis in the neurons (375).

Cu/Zn超氧化物歧化酶的突变是导致25%的家族性肌萎缩侧索硬化症的病因。一些与家族性肌萎缩侧索硬化症有关的Cu/Zn超氧化物歧化酶突变体对锌的亲和力降低。在一些变种人中多达30倍。野生型超氧化物歧化酶对锌的损失大约是该酶催化过氧亚硝酸盐介导的酪氨酸生成的效率的两倍,说明超氧化物歧化酶在肌萎缩侧索硬化症中的作用可能是锌丢失的间接结果。蛋白质结合酪氨酸的硝化作用是一种永久性的修饰,会对蛋白质功能产生不利影响.因此,与肌萎缩侧索硬化症相关的超氧化物歧化酶突变体的毒性可能与锌丢失后蛋白质硝化的催化作用增强有关。在最近的一项研究中,野生型和肌萎缩型侧索硬化症突变型超氧化物歧化酶都能保护富含铜和锌的运动神经元。当同样的蛋白质被制成锌d因此,所有这些都引起了神经元的凋亡。

Lammich et al (376) report endogenous -secretase activity was inhibited by a dominant negative form of a disintegrin and metalloprotease, namely ADAM 10 (see OMIM 602192), with a point mutation in the zinc binding site. ADAM 10 is associated closely with an -secretase activity; the authors found it to cleave a site within the amyloid  peptide sequence. It appears that increasing ADAM 10 expression or activity could possibly promote proteolytic cleavage of amyloid precursor protein within the amyloid  sequence, thus preventing the protein from being converted into insoluble amyloid , the proteinaceous component of amyloid plaques in brains of patients with Alzheimer disease. Because a mutation in the zinc binding site was found, it might be possible to stimulate the enzyme and rate of reaction via zinc administration.

Lambert等人,据报道,分解素和金属蛋白酶的一种主要阴性形式抑制了内源性分泌酶的活性,即Adam 10(见OMIM 602192),在锌结合位点发生点突变。ADAM10与-分泌酶活性紧密相关;作者发现它能切割淀粉样肽序列中的一个位点。在淀粉样蛋白序列中,增加ADAM 10的表达或活性可能促进淀粉样前体蛋白的蛋白水解,从而防止蛋白质转化为不溶性淀粉样蛋白。阿尔茨海默病患者大脑中淀粉样斑,块的蛋白质组分。因为锌结合位点的突变被发现了,可能通过锌给药刺激酶和反应速率。

Although zinc is a component of hundreds of important enzymes, the range between adequacy and toxicity is narrow (10). It is unclear whether zinc interventions will be successful.

尽管锌是数百种重要酶的组分,充分性和毒性之间的范围很窄。目前尚不清楚锌干预措施是否会成功。

Potassium 钾

Inosine 5 -monophosphate dehydrogenase (OMIM 146690)

肌苷5磷酸脱氢酶  (OMIM 146690)

catalyzes the oxidation of inosine 5 -monophosphate to xantho-sine 5 -monophosphate with the concomitant reduction of NAD to NADH. E. coli inosine 5 -monophosphate dehydrogenase is activated by several cations including potassium. K+ increases the rate constant for the pre–steady state burst of NADH pro-duction, possibly by increasing the affinity of NAD. Three mutant enzymes have been identified that increase the value of Km for K+: Asp13→Ala, Asp50→Ala, and Glu469→Ala. Both Asp13 and Glu469 appear to interact with the K+ binding site identified in Chinese hamster inosine 5 -monophosphate dehy-drogenase (377). (See also the discussion of BCKAD in the sec-tion on thiamine.)

催化5-磷酸肌苷氧化为黄嘌呤-正弦-5-单磷酸,同时将NAD还原为NADH.大肠杆菌肌苷5-磷酸脱氢酶由钾等几种阳离子激活.K可能通过增加NAD的亲和力来增加NADH生产的预稳态爆发的速率常数。已鉴定出三种能提高K的Km值的突变酶:Asp13→Ala、Asp50→Ala和Glu469→Ala。Asp13和Glu469似乎都与C中识别的K结合位点相互作用中国仓鼠肌醇5-单磷酸酯脱氢酶

MAXI B VITAMINS  复合B族维生素

Health food and drug stores sell a variety of high-dose B vita-min pills called B50, B100, and similar formulations. The time-release B100 pill contains 100 mg each of thiamine, riboflavin, niacin, pyridoxine, and pantothenic acid; 100 g each of vitamin B-12 and biotin; and 400 g folate. Except for folate and biotin, which are at or near the DRIs, these amounts approximate the high intakes discussed in this review. Until now, there has been little general support for high-dose B vitamin intake, so the presence of these pills on the market is puzzling. This review sug-gests that for some persons there might be a benefit from high-dose B vitamin treatment, although when there is, it would be desirable to find out which vitamin is responsible and to opti-mize the dose.

健康食品和药店出售各种高剂量的B型维生素A-min丸,称为B50,B 100和类似的配方。该缓释B100丸剂含有100mg的硫胺素、核黄素、烟酸、维生素B6和泛酸;维生素B-12和生物素各100克;叶酸400克。除了处于或接近DRI的叶酸和生物素外,这些量接近本综述中讨论的高摄入量。到目前为止,几乎没有人普遍支持高剂量维生素B的摄入,因此,这些药片在市场上的重要性是令人费解的。本综述认为,对于某些人来说,高剂量的B维生素治疗可能会有好处,虽然当存在时,需要发现哪些维生素是负责的,并对该剂量进行调理。

CONCLUSION 结论

High-dose vitamin therapies have been efficacious in amelio-rating 50 genetic diseases. The diseases are usually due to variant enzymes with decreased affinity (increased Km) for vita-min-derived cofactors. Feeding high doses of the vitamin raises the tissue cofactor concentrations and thereby increases the activ-ity of the defective enzyme. Several polymorphisms in which the variant amino acid is at a coenzyme binding site result in reduced enzymatic activity, which is likely to be remediable by raising cellular cofactor concentrations through the administration of high doses of vitamins. Remediation would be useful if the primary reason for the selection of the polymorphism is no longer important and the polymorphism has deleterious side effects.

高剂量维生素治疗对50种遗传病进行了有效评价.这些疾病通常是由于对于Vita-min衍生的辅因子具有降低的亲和力(增加的Km)的变体酶所致。摄入高剂量的维生素会增加组织辅助因子的浓度,从而提高缺陷酶的活性。在几个多态中,变异氨基酸位于辅酶结合位点,导致酶活性降低,通过服用高剂量的维生素来提高细胞内辅因子的浓度,这可能是可以补救的。如果选择多态性的主要原因不再重要,补救将是有用的并且该多态性具有有害的副作用。

The examples discussed here are likely to represent only a small fraction of the total number of defective enzymes that would be responsive to therapeutic vitamins. It seems likely that many additional enzymes requiring PLP, TPP, NAD(P), FAD, or other cofactors will be found to have genetic variants that affect cofactor binding. For example, the ENZYME database includes > 100 entries each for FAD- and PLP-requiring enzymes (6), but we have found documentation of binding defects in <12 enzymes for either cofactor. Thus, both with polymorphisms and with the range of mutations causing severe to mild effects on phenotype, high vitamin administration is a potential remedy, and individu-als with additional information pertaining to the topics discussed in this review are encouraged to contribute to the growing body of knowledge at www.KmMutants.org. With the advent of genomics and individual polymorphism assessment, it will become possible to customize vitamin therapies to suit the geno-typic, and thus more specific, needs of individuals, instead of treating the phenotype. For now, for many of the conditions dis-cussed, high-dose B vitamin pills or high doses of individual vitamins are available to physicians as reasonably safe and potentially helpful therapies; however, the possibility of some accompanying side effects should not be discounted.

这里讨论的例子很可能只代表对治疗性维生素有反应的有缺陷的酶总数的一小部分。可能会发现需要PLP、TPP、NAD(P)、FAD或其它辅助因子的许多附加酶具有影响辅因子结合的遗传变体。例如,酶数据库包括fad和plp所需酶的>100个条目。但是我们已经发现了任何一种辅助性因子在<12酶中结合缺陷的文献。因此,无论是多态性还是突变范围都会对表型造成严重或轻微的影响,服用高剂量的维生素是一种潜在的治疗方法,并鼓励提供与本综述中讨论的主题有关的更多信息的不可分割的ALS为k的不断增长作出贡献。网址:www.kmMutants.org。随着基因组学和个体多态性评估的出现,它将成为可能的定制维生素疗法,以适应基因类型,从而更具体的个人需要,而不是治疗表型。就目前而言,对于许多情况,医生认为高剂量的B类维生素丸或高剂量的个别维生素是相当安全的和潜在的有帮助的治疗,然而,一些伴随的副作用的可能性不应被低估。

We acknowledge the helpful comments of Giovanna Ferro-Luzzi Ames, Hani Atamna, Samuel Barondes, Victor Hugo Espin, Balz Frei, Alexander Glazer, Christine Hansen, Arnold Huang, Jack Kirsch, Bill Klitz, Mark Levine, Jiankang Liu, Rowena Matthews, Victor McKusick, John Nides, Terry Schultz, Mark Shigenaga, Christine Skibola, Martyn Smith, and Lynn Wallock.

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