Submitted to: Advances in Nutrition
Publication Type: Review Article
Publication Acceptance Date: 6/20/2012
Publication Date: 6/20/2012
Publication URL: http://advances.nutrition.org/content/3/1/54.full.pdf+html
Citation: Allen, L.H. 2012. Vitamin B-12. Advances in Nutrition. 3:54-55.
Technical Abstract: Vitamin B-12 is a cofactor for 2 enzymes. In the cytoplasm, methionine synthase requires vitamin B-12 in the form of methylcobalamin and catalyzes the conversion of homocysteine to methionine by transfer of a methyl group from methyltetrahydrofolate.This enzyme links the methylation pathway through synthesis of the methyl donor S-adenosyl methionine and the pathway in which purine and pyrimidine are synthesized via generation of tetrahydrofolate. In the form of 59-deoxyadenosylcobalamin, vitamin B-12 is also required for the mitochondrial enzyme methylmalonyl CoA mutase, which converts methylmalonyl CoA to succinyl CoA, a step in the oxidation of odd-chain fatty acids and catabolism of ketogenic amino acids. Thus, vitamin B-12 is important for DNA synthesis, regenerating methionine for protein synthesis and methylation, and preventing homocysteine accumulation (1).