PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.
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DOI：
10.1126/science.44.1129.244
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发表时间：
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影响因子：
56.9
通讯作者：
V. Gates;.. M. L. Ludwig-M.-L.-Ludwig-2273875465;J. A. Hartsuck;T. A. Steitz;H. Muirhead;J. C. Coppola;G. N. Reeke
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作者：
V. Gates;.. M. L. Ludwig-M.-L.-Ludwig-2273875465;J. A. Hartsuck;T. A. Steitz;H. Muirhead;J. C. Coppola;G. N. Reeke
维生素B12（氰钴胺）组的维生素显然参与了几个代谢过程。1例如，Helleiner和Woods 2报道，大肠杆菌突变体的无细胞提取物需要甲硫氨酸或维生素B12才能生长，当补充维生素B12时，在含有同型半胱氨酸、丝氨酸和三磷酸腺苷的反应混合物中更快地形成甲硫氨酸。这表明维生素在某些时候参与甲基的形成或转移。最近，Wagle等人3发现维生素B12刺激氨基酸掺入维生素B12缺乏大鼠微粒体可溶性蛋白系统的蛋白质中。用未指明的抗B12化合物进行的抑制实验表明，维生素参与氨基酸的活化。维生素B12参与莱氏乳杆菌脱氧核糖合成和二硫基还原的证据也已提出。虽然这些和其他研究1已经确定了几个代谢过程中，钴直接或间接参与，这些化合物的确切作用尚未确定。没有具体的酶功能已被证明，并没有辅酶形式的维生素已被描述。我们希望报告的辅酶形式的假维生素B12的分离所需的谷氨酸盐的无颗粒提取物破伤风梭菌的分解。辅酶参与谷氨酸碳骨架的重排，形成支链氨基酸，3-甲基天冬氨酸。本实验室先前的研究表明，C.破伤风吗啉通过一系列完全不同于三羧酸循环的反应发生。这个序列中的关键化合物是中康酸盐，一种支链C5二羧酸。谷氨酸到中康酸和氨的可逆转化涉及以下两个反应：
Vitamins of the B12 (cyanocobalamin) group apparently participate in several metabolic processes.1 For example, Helleiner and Woods2 reported that a cellfree extract of an Escherichia coli mutant, which requires either methionine or vitamin B12 for growth, forms methionine more rapidly in a reaction mixture containing homocysteine, serine, and adenosine triphosphate when supplemented with vitamin B12. This indicates that the vitamin participates at some point in methyl group formation or transfer. More recently, Wagle et al.3 found that vitamin B12 stimulates incorporation of amino acids into the proteins of a microsome-soluble protein system of vitamin B12-deficient rats. Inhibition experiments with an unspecified anti-B12 compound indicated that the vitamin is involved in the activation of amino acids. Evidence for the involvement of vitamin B12 in the synthesis of deoxyribose by Lactobacillus leichmanii"' 5 and in the reduction of dithio groups8' I has also been presented. Although these and other studies1 have identified several metabolic processes in which the cobalamins participate directly or indirectly, the precise roles of these compounds have not been established. No specific enzymatic function has been demonstrated, and no coenzyme form of the vitamin has been described. We wish to report the isolation of a coenzyme form of pseudovitamin B12 which is required for the decomposition of glutamate by particle-free extracts of Clostridium tetanomorphum. The coenzyme is involved in the rearrangement of the carbon skeleton of glutamate to form a branched chain amino acid, ,3-methylaspartate. Previous studies in this laboratory8 have shown that the fermentation of glutamate by C. tetanomorphum occurs by a sequence of reactions that is entirely different from the tricarboxylic acid cycle. A key compound in this sequence is mesaconate, a branched-chain C5 dicarboxylic acid. The reversible conversion of glutamate to mesaconate and ammonia involves the following two reactions: