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see coenzymecoenzyme
, any one of a group of relatively small organic molecules required for the catalytic function of certain enzymes. A coenzyme may either be attached by covalent bonds to a particular enzyme or exist freely in solution, but in either case it participates intimately in
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; vitaminvitamin,
group of organic substances that are required in the diet of humans and animals for normal growth, maintenance of life, and normal reproduction. Vitamins act as catalysts; very often either the vitamins themselves are coenzymes, or they form integral parts of coenzymes.
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(or Vitamin B12), C63H88CoN14O14P, a cobalt-corrin complex in which the cobalt atom is bonded to a cyano group, a nucleotide residue, and four reduced pyrrole rings; molecular weight, 1355.40. Cyanocobalamin is a dark-red crystalline compound, which is soluble in water and polar organic solvents. It was first isolated in crystalline form from cattle liver. Its structure was established by A. Todd and D. Crowfoot Hodgkin and their co-workers.

The primary sources of cyanocobalamin in nature are microorganisms; cyanocobalamin is synthesized by several bacteria, by actinomycetes, and by blue-green algae. It occurs in almost all animal tissues. It is not encountered, as a rule, in the tissues of higher plants (legume tubers are an exception). In ruminants, it is synthesized in sufficient amounts by the microflora of the intestine and the rumen. In man and several higher animals, such as birds and hogs, its synthesis by intestinal microflora is insufficient, and thus the vitamin must be obtained from food. The daily requirement for humans is about 5 μg. The major sources of the vitamin are liver, kidneys, fish meal, and milk.

In the form of its coenzymes methylcobalamin and deoxyadenosylcobalamin, cyanocobalamin participates in the enzymic reactions involved in hematopoiesis and facilitates normal liver function and nerve fiber regeneration. It is produced by microbiological synthesis using propionic-acid bacteria for the fermentation process.

Vitamin B12 is used for the treatment of pernicious anemia and other anemias, as well as of diseases of the central and peripheral nervous systems and the liver. It is prescribed in solutions for intramuscular injections. (See alsoVITAMINS; ANEMIA; and COBALAMINS.)


Smith, L. Vitamin B12. Moscow, 1962. (Translated from English.)
Friedrich, W. Vitamin B12 und Verwandte Corrinoide, 3rd ed. Stuttgart, 1975.



vitamin B12
References in periodicals archive ?
Again it has been seen that aquocobalamin (H,O-Cbl (but not cyanocobalamin [CN-Cbl], methylcobalamin [Me-Cbl], or adenosyl-cobalamin [Ado-Cbl]) reacts with NO (48).
Metanx([R]) contains the active forms of folate and Vitamins B12 and B6 (L-methylfolate, methylcobalamin, and pyridoxal 5'-phosphate, respectively).
However, only traces of cyanocobalamin occur naturally in the human body, which contains primarily hydroxocobalamin, adenosylcobalamin, and methylcobalamin.
Quick Melt Fully Active B12 features a pleasant-tasting ORTHO vitamin featuring methylcobalamin B12.
Addition of the methylcobalamin displayed a significant methylation of iAs (18%), with MM[A.
The major forms are hydroxocobalamin or aquocobalamin (OHCbl) and the 2 coenzyme forms of Cbl, 5'-deoxyadenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) (1, 13).
2) An optimized blend of essential minerals and vitamins, including vitamin forms designed for greater bioavailability: vitamin D3, L-5-methyltetrahydrofolate (folate) and methylcobalamin (B12)
Ninety-eight patients (mean age, 67 years) with subacute postherpetic neuralgia on the torso (pain had been present for 30 to 120 days after the onset of the rash) and a mean pain score of 7 on a scale of 0 to 10 (higher scores indicate worse pain) were randomly assigned to receive local subcutaneous injections of methylcobalamin (500 pg/m1) or 1% lidocaine, or oral methylcobalamin (500 pg 3 times per day) for 4 weeks.
Athletic Pro- For the athlete Athletic Pro is a compound containing ATP, L-Carnitine, Inositol, Methionine and Methylcobalamin B12.
Every Body's Multiple also provides vitamins B6, B12 and folic acid in their active forms: P-5-P, methylcobalamin and L-methylfolate Additionally, Every Body's Multiple provides a full range of other necessary ingredients, including vitamin D3 and vitamin E from a d-alpha and mixed tocopherol complex, the way nature intended
Zakharyan and Aposhian (1999) reported that in vitro incubation of methylcobalamin ([CH.
3] Methylcobalamin is the cofactor for methionine synthase, the enzyme that mediates HCY remethylation to methionine.