Babior B M
Department of Basic and Clinical Research, Research Institute of Scripps Clinic, La Jolla, CA 92037.
Biofactors. 1988 Jan;1(1):21-6.
Adenosylcobalamin (AdoCbl)-dependent rearrangements are a group of reactions with no obvious precedents in organic chemistry. In every case, they are characterized by a mechanism in which a hydrogen atom on one carbon atom exchanges places with a group X on an adjacent carbon: (formula; see text) Much experimental work indicates that an AdoCbl rearrangement is initiated by homolysis of the C-Co bond of the cofactor. The migrating hydrogen is then abstracted from the substrate by the resulting 5'-deoxyadenosyl radical, or by a second radical that is generated elsewhere at the active site, and, after the migration of group X, is returned to the product in a similar reaction. In at least some of the rearrangements, group X migration may occur via a cation radical intermediate that formed by the departure of X with its electrons, a process assisted by the unpaired electron left behind on the adjacent carbon after the abstraction of the migrating hydrogen. Once C-Co bond cleavage has initiated the reaction by producing a free radical at the active site, the corrin ring plays no further role in the rearrangements.
腺苷钴胺素（AdoCbl）依赖性重排反应是有机化学中一组无明显先例的反应。在每种情况下，它们的特征机制是一个碳原子上的氢原子与相邻碳原子上的基团X交换位置：（分子式；见正文）大量实验工作表明，AdoCbl重排反应由辅因子的C-Co键均裂引发。然后，迁移的氢被生成的5'-脱氧腺苷自由基或在活性位点其他位置产生的第二个自由基从底物中提取出来，并且在基团X迁移后，通过类似反应回到产物中。在至少一些重排反应中，基团X的迁移可能通过阳离子自由基中间体发生，该中间体由X带着其电子离去形成，此过程由迁移氢被提取后相邻碳原子上留下的未成对电子协助。一旦C-Co键断裂通过在活性位点产生自由基引发反应，咕啉环在重排反应中就不再起进一步作用。
