![]() ![]() The process starts in the mouth when food is mixed with saliva. Vitamin B12 is bound to protein in food and must be released before it is absorbed. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the metabolism of propionate, a short-chain fatty acid. Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 different substrates, including DNA, RNA, proteins, and lipids. ![]() 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.
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