title: Mechanisms of coenzyme B12-dependent rearrangements.
abstract: Coenzyme B12 serves as a cofactor in various enzymatic reactions in which a hydrogen atom is interchanged with a substituent on an adjacent carbon atom. Measurement of the dissociation energy of the coenzyme's cobalt-carbon bond and studies of the rearrangement of model free radicals related to those derived from methylmalonyl-coenzyme A suggest that these enzymatic reactions occur through homolytic dissociation of the coenzyme's cobalt-carbon bond, abstraction of a hydrogen atom from the substrate by the coenzyme-derived 5'-deoxyadenosyl radical, and rearrangement of the resulting substrate radical. The only role thus far identified for coenzyme B12 in these reactions--namely, that of a free radical precursor--reflects the weakness, and facile dissociation, of the cobalt-carbon bond.
authors.forename: J
authors.initials: J
authors.lastname: Halpern
mesh_terms: D002244:Carbon / Q000378:metabolism; D055598:Chemical Phenomena; D002621:Chemistry; D002627:Chemistry, Physical; D003035:Cobalt / Q000378:metabolism; D003038:Cobamides / Q000378:metabolism*; D004734:Energy Metabolism; D005609:Free Radicals; D008765:Methylmalonyl-CoA Mutase / Q000378:metabolism
chemical_list: D003038:Cobamides; D005609:Free Radicals; D003035:Cobalt; D002244:Carbon; D008765:Methylmalonyl-CoA Mutase; C000913:cobamamide