What are the Functions of Vitamin B12 (Cobalamins)?
Functions Three main enzymatic reactions regarding vitamin B12 have been noted to occur in humans. The first reaction requires methylcobalamin as a coenzyme in the conversion of homocysteine into methionine. This reaction occurs in the cytosol of the cell. The reaction is intrinsic to the production of tetrahydrofolate (THF). The production of THF is irreversible and requires vitamin B12, therefore, a B12 deficiency can trap folate in its methyl form (also known as the folate-methyl trap), which in turn affects purine and thymidylate synthesis. A second set of reactions requiring B12 are those catalyzed by mutases. These reactions occur within the mitochondria. These include the production of succinyl CoA, a Krebs cycle intermediate. Mutase enzymes are also intrinsic in the oxidation of fatty acids. A defect in mutase activity results in impai.red muscle activity and an accumulation of methylmalonyl CoA and methylmalonic acid. The branched-chain amino acid leucine is also catalyzed by
