 ("R")-Methylmalonyl-CoA is converted to succinyl-CoA, an intermediate in the tricarboxylic acid cycle, by methylmalonyl-CoA mutase, an enzyme requiring 

cobalamin to catalyze the carbon-carbon bond migration.The methylmalonyl-CoA mutase mechanism begins with the cleavage of the bond between the 5' - of 5'-deoxyadenosyl and the cobalt, which is in its 3+ oxidation state (III), which produces a 5'-deoxyadenosyl radical and cobalamin in the reduced Co(II) oxidation state.Next, this radical abstracts a hydrogen atom from the methyl group of methylmalonyl-CoA, which generates a methylmalonyl-CoA radical.