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首页> 外文期刊>Chemistry: A European journal >Homocoenzyme B-12 and bishomocoenzyme B-12: Covalent structural mimics for homolyzed, enzyme-bound coenzyme B-12
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Homocoenzyme B-12 and bishomocoenzyme B-12: Covalent structural mimics for homolyzed, enzyme-bound coenzyme B-12

机译：同型辅酶B-12和Bishomocoenzyme B-12：均质的酶结合型辅酶B-12的共价结构模拟物

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摘要

Efficient electrochemical syntheses of "homocoenzyme B-12" (2, Co-beta-(5'-doexy-5'-adenosyl-methyl)-cob(m)alamin and "bishomocoenzyme B-12" (3, Co-beta-[2-(5'-deoxy-5'-adenosyl)ethyl]-cob(III) alamin) are reported here. These syntheses have provided crystalline samples of 2 and 3 in 94 and 77% yield, respectively. In addition, indepth investigations of the structures of 2 and 3 in solution were carried out and a high-resolution crystal structure of 2 was obtained. The two homologues of coenzymeB(12) (2 and 3) are suggested to function as covalent structural mimics of the hypothetical enzyme-bound "activated" (that is, "stretched" or even homolytically cleaved) states of the B-12 cofactor. From crude molecular models, the crucial distances from the corrin-bound cobalt center to the C5' atom of the (homo)adenosine moieties in 2 and 3 were estimated to be about 3.0 and 4.4 Angstrom, respectively. These values are roughly the same as those found in the two "activated" forms of coenzyme B-12 in the crystal structure of glutamate mutase. Indeed, in the crystal structure of 2, the cobalt center was observed to be at a distance of 2.99 Angstrom from the C5' atom of the homoadenosine moiety and the latter was found to be present in the unusual syn conformation. In solution, the organometallic moieties of 2 and 3 were shown to be rather flexible and to be considerably more dynamic than the equivalent group in coenzyme B-12. The homoadenosine moiety of 2 was indicated to occur in both the syn and the anti conformations.
机译：“同型辅酶B-12”（2，Co-beta-（5'-doexy-5'-腺苷甲基）-cob（m）丙氨酸和“ bishomocoenzyme B-12”（3，Co-beta-此处报道了[2-（5'-脱氧-5'-腺苷基）乙基]-钴（III）阿拉明），这些合成物分别提供了2％和3％的结晶样品，产率分别为94％和77％。对溶液中2和3的结构进行了研究，获得了2的高分辨率晶体结构，辅酶B（12）（2和3）的两个同源物被认为是假想酶的共价结构模拟物B-12辅因子的“结合”状态（即“拉伸”或什至被同质裂解）从粗分子模型看，从结合柯林蛋白的钴中心到（均质）C5'原子的临界距离估计2和3中的腺苷部分分别约为3.0和4.4埃，这些值与两种“活化”形式的辅酶B-谷氨酸突变酶的晶体结构中的12。实际上，在2的晶体结构中，观察到钴中心与高腺苷部分的C5'原子的距离为2.99埃，并且发现后者以不寻常的顺式构象存在。在溶液中，2和3的有机金属部分显示出相当强的柔韧性，并且比辅酶B-12中的等效基团具有更大的动态性。表明2的高腺苷部分同时存在于顺式和反式构象中。

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