On the mechanism of catalysis by vitamin B12.

The requirements for alkylation and binding of nitrogenous ligands to cobalamins and cobinamides suggest that the central cobalt atom can exist either approximately in the plane of the corrin or axially displaced above this plane. Distortion of the normal octahedral complex by axial displacement results when the dimethylbenzimidazole moiety of the coenzyme is prevented from coordinating with the cobalt. A general hypothesis of B(12) coenzyme catalysis that involves the potential of Co(III)-R([unk]) and Co(I)-R([unk]) transitions is proposed on the basis of these considerations.