The vitamin is a cobalt-containing coordination compound generated by intestinal microbes, and a natural water-soluble vitamin of the B-complex family that must combine with Intrinsic Factor for absorption by the intestine.
Cobalamins cannot be synthesized by higher organisms and must be supplied with the diet. In humans, the lack of dietary cobalamin, or malfunctioning of absorption or of the enzymatic catalysis may provoke neurological disorders, in addition to pernicious anaemia.
However, a highly modulated absorption ability and transport through body fluids prevents any possible shortage even after many years of no intake.
Cobalamin is an organometallic factor composed of a tetrapyrrolic corrinic ring with a cobalt atom coordinated to four equatorial nitrogen atoms.
Vitamin B12 in food is bound to protein and is released in the stomach by the acid environment and by proteolysis of binders by pepsin. The released vitamin B12 initially binds to R-binders, which are dietary proteins that have affinity for vitamin B12.
Cobalamin is necessary for hematopoiesis, neural metabolism, DNA and RNA production, and carbohydrate, fat, and protein metabolism. B12 improves iron functions in the metabolic cycle and assists folic acid in choline synthesis.
B12 metabolism is interconnected with that of folic acid. Vitamin B12 deficiency causes pernicious anemia, megaloblastic anemia, and neurologic lesions.
Vitamin B12: Structure and functions
