Scientific Reference
Vitamin B12
Evidence profile: Controlled human evidence
Vitamin B12 is the collective name for the cobalamins, organometallic compounds built around a corrin ring that holds a single metal ion. Cyanocobalamin (CAS 68-19-9) carries a cyanide group as its upper ligand and is the most chemically stable of the common forms. Other natural forms differ in that ligand: methylcobalamin carries a methyl group, adenosylcobalamin a 5′-deoxyadenosyl group and hydroxocobalamin a hydroxyl group. Cobalamins are made in nature only by certain bacteria and archaea. The chemistry and enzymology of the group have been worked out over decades, and current laboratory work concerns their uptake and transport proteins, their processing inside cells and the enzymes that use them.
Mechanism of Action
Two mammalian enzymes use cobalamin cofactors. Cytosolic methionine synthase uses methylcobalamin to transfer a methyl group from 5-methyltetrahydrofolate to homocysteine, forming methionine and freeing tetrahydrofolate; this ties cobalamin to folate metabolism and to the supply of S-adenosylmethionine for methylation reactions. Mitochondrial methylmalonyl-CoA mutase uses adenosylcobalamin to convert methylmalonyl-CoA into succinyl-CoA, a step in the breakdown of odd-chain fatty acids and several amino acids. Cyanocobalamin is not itself a cofactor: cells are reported to remove the cyanide ligand and convert the core into the two working forms.
Molecular Information
- Type: Vitamin (cyanocobalamin)
- Molecular weight: 1355.4 g/mol
- Molecular formula: C63H88CoN14O14P
Published Research
The Efficacy of Oral Vitamin B12 Replacement for Nutritional Vitamin B12 Deficiency
Sezer RG et al. · Journal of pediatric hematology/oncology · 2018 · Clinical
PMID 29189512 — View on PubMedOral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial
Eussen SJ et al. · Archives of internal medicine · 2005 · Clinical
PMID 15911731 — View on PubMedVitamin B12 deficiency in patients undergoing bariatric surgery: preventive strategies and key recommendations
Majumder S et al. · Surgery for obesity and related diseases : official journal of the American Society for Bariatric Surgery · 2013 · Review
PMID 24091055 — View on PubMed