Vitamin B12 or cyanocobalamin (cobalt contained in corrinoid ring structures) is a coenzymes for two enzymes i.e. methionine synthase and methyl malonyl CoA mutase. In the quest for finding the reasons for pernicious anemia, it was discovered to be the "extrinsic factor", necessary to react with the "intrinsic factor" produced by stomach, to be absorbed and thereby prevent the disease.