Methionine synthase catalyzes the conversion of homocysteine to the essential amino acid methionine. Vitamin B12 functions as a cofactor for two enzymes, methionine synthase and L-methylmalonyl-CoA mutase. Vitamin B12 is required for the development, myelination, and function of the central nervous system healthy red blood cell formation and DNA synthesis. However, two others forms, hydroxycobalamin and cyanocobalamin, become biologically active after they are converted to methylcobalamin or 5-deoxyadenosylcobalamin. Methylcobalamin and 5-deoxyadenosylcobalamin are the metabolically active forms of vitamin B12. Because vitamin B12 contains the mineral cobalt, compounds with vitamin B12 activity are collectively called “cobalamins”. Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. For a general overview of Vitamin B12, see our consumer fact sheet on Vitamin B12. This is a fact sheet intended for health professionals. Health Risks from Excessive Vitamin B12.
Groups at Risk of Vitamin B12 Inadequacy.
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