Cobalamin (vitamin B12) exists in a number of different chemical forms. The molecule consists of two halves: a 'planar group' and 'nucleotide' set at right angles to it (Figure 5.5). The planar group is a corrin ring and the nucleotide consists of the base, 5,6-dimethylbenziminazole, and a phosphorylated sugar, ribose-s-phosphate. In nature, the vitamin is mainly in the
5'-deoxyadenosyl (ado) form. This is the main form in human tissues and is located in the mitochondria. It serves as the cofac-tor for the enzyme methylmalonyl CoA mutase. The other major natural cobalamin is methylcobalamin, the main form in human plasma, as well as the cytosolic form in cells. It serves as the cofactor for the enzyme methionine synthase. There are also minor amounts of hydroxocobalamin, which is the form to which methyl- and ado-cobalamin are rapidly converted by exposure to light, hydroxocobalamin having its cobalt atom in the fully oxidized Cbl3+ state, whereas the cobalt exists as reduced Cbl1+ in the methyl- and ado-cobalamin forms (Figure 5.2). A glutathionyl cobalamin form has also been identified.
Was this article helpful?
All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.