Scientific Reference
Vitamin B12
Evidence profile: Controlled human evidence
Vitamin B12 is the collective name for the cobalamins, organometallic molecules built round a corrin ring that holds a single cobalt ion. Cyanocobalamin (CAS 68-19-9) has a cyanide group as its upper ligand and is the most chemically stable of the common forms. The other natural forms differ in that ligand: methylcobalamin has a methyl group, adenosylcobalamin a 5'-deoxyadenosyl group, and hydroxocobalamin a hydroxyl. Only certain bacteria and archaea make cobalamins in nature. The chemistry and enzymology of the group were worked out over decades; current laboratory interest is in uptake and transport proteins, processing inside cells, and the enzymes that use them.
Mechanism of Action
Two mammalian enzymes depend on cobalamin cofactors. Cytosolic methionine synthase uses methylcobalamin to move a methyl group from 5-methyltetrahydrofolate to homocysteine, forming methionine and releasing tetrahydrofolate, which links cobalamin to folate metabolism and to the supply of S-adenosylmethionine for methylation reactions. Mitochondrial methylmalonyl-CoA mutase uses adenosylcobalamin to convert methylmalonyl-CoA to succinyl-CoA, a step in breaking down odd-chain fatty acids and several amino acids. Cyanocobalamin is not itself a cofactor: cells are reported to strip the cyanide and convert the core into the two working forms.
Molecular Information
- Type: Vitamin (cobalamins)
- 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