Description | Cob(I)alamin is the substrate of the enzyme ATP:cob(I)alamin adenosyltransferase (EC 2.5.1.17), that converts reduced cob(I)alamin to the adenosylcobalamin co-factor required for the functional activity of methylmalonyl-CoA mutase (EC 5.4.99.2). Mutations in the human MMAB gene result in a block in adenosylcobalamin synthesis and are responsible for the cblB complementation group of inherited vitamin B12 disorders. Vitamin B12 (cobalamin) is a complex cobalt-containing molecule that is essential to human health. It is synthesized in bacteria where it catalyzes numerous methyl transfer and intramolecular rearrangement reactions. In mammals, it is the co-factor of only two enzymes: methionine synthase, which catalyzes the transfer of a methyl group from methyltetrahydrofolate to homocysteine to form methionine, and methylmalonyl-CoA mutase, which catalyzes the rearrangement of methylmalonyl-CoA to form succinyl-CoA. For both enzymes, the vitamin must be modified through intracellular metabolism to co-factor forms: methylcobalamin (MeCbl)1 for methionine synthase and adenosylcobalamin (AdoCbl) for methylmalonyl-CoA mutase. (PMID: 16439175) |