Vitamin B12
Also known as: Cobalamin, Cyanocobalamin, Methylcobalamin
An essential cobalt-containing cofactor for methionine synthase and methylmalonyl-CoA mutase, supplied as a ready-to-use solution.
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Molecular Data
- Class
- Cobalt-containing corrinoid vitamin / Enzyme cofactor (not a peptide)
- Molecular Weight
- 1,355.37 Da
- Molecular Formula
- C₆₃H₈₈CoN₁₄O₁₄P (cyanocobalamin)
- Half-Life
- Long — hepatic stores are measured in years, and plasma clearance depends on transcobalamin binding
Mechanism of Action
B12 is a vitamin, not a peptide — it is included in this library because it is a compound we supply and because it appears as a constituent of the lipotropic blend. Cobalamin is the largest and most structurally complex of the vitamins, built around a corrin ring with a central cobalt atom.
- Methionine synthase cofactor: Methylcobalamin is the cofactor for methionine synthase, which transfers a methyl group from 5-methyltetrahydrofolate to homocysteine to regenerate methionine. A B12 deficit therefore traps folate in its methyl form and raises homocysteine.
- Methylmalonyl-CoA mutase cofactor: Adenosylcobalamin is the cofactor for the mitochondrial enzyme converting methylmalonyl-CoA to succinyl-CoA, the entry point for odd-chain fatty acids and several amino acids into the citric acid cycle. Blocking this step raises methylmalonic acid, the more specific of the two deficiency markers.
- A multistep transport pathway: Nielsen and colleagues describe cobalamin trafficking from food to the body's cells as involving more than fifteen gene products — haptocorrin, intrinsic factor, cubilin, amnionless, transcobalamin and its receptor among them. Most non-dietary deficiency is a failure somewhere along that chain rather than low intake.
- Cyanocobalamin versus methylcobalamin: Cyanocobalamin is the stable synthetic form used in most solutions; it is converted intracellularly to the two active coenzyme forms. Methylcobalamin is one of those active forms supplied directly.
See the LIPO-C entry for the lipotropic blend in which B12 appears alongside methionine, inositol and choline.
Research History
B12 has one of the best-documented histories in nutritional biochemistry. Minot and Murphy's demonstration in 1926 that a liver diet reversed pernicious anaemia earned a Nobel Prize in 1934, though the active factor itself was not isolated until 1948. Dorothy Hodgkin determined the structure by X-ray crystallography in 1956, work recognised with the 1964 Nobel Prize in Chemistry.
The molecular detail filled in over the following decades: the two coenzyme forms, the enzymes they serve, and the elaborate binding-protein relay that carries cobalamin across the gut wall and into cells. That relay is why deficiency has so many distinct causes — gastric atrophy, loss of intrinsic factor, ileal disease, and a set of inherited transport disorders each interrupt it at a different point.
Unlike most compounds in this library, B12 is not investigational. Its physiology is settled, and injectable cobalamin is a long-established clinical treatment for deficiency. Its presence here is as a supplied reagent and blend constituent, and the material we sell is for laboratory research use rather than for treating a deficiency.
Notable Studies
Nielsen MJ, Rasmussen MR, Andersen CBF, Nexø E, Moestrup SK. · Nature Reviews Gastroenterology & Hepatology
Maps the full absorption and distribution pathway across more than fifteen gene products, and explains why interruptions at different points produce the heterogeneous clinical picture of B12 deficiency.