| description | Protein which contains at least one cobalamin as cofactor, e.g methylmalonyl-CoA mutase, or which binds and/or transports cobalamin, such as intrinsic factor or transcobalamins. Cobalamin, which is synthesized by microorganisms, has equatorial sites occupied by a tetrapyrrol ring structure (corrin ring) with a cobalt(III) ion in the center, one axial site occupied by an intramolecularly-bound dimethylbenzimidazole and the other axial site occupied by a number of different ligands such as water (aquacobalamin), cyanide (cyanocobalamin=vitamin B12), glutathione (glutathionylcobalamin), 5'deoxyadenosine (adenosylcobalamin=coenzyme B12) or a methyl group (methylcobalamin). It is a prosthetic group of certain mammalian enzymes, where it is essential for the normal maturation and development of erythrocytes. A deficiency in the diet or more frequently the failure to absorb the vitamin give rise to pernicious anemia |
