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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 ?
Efficacy and safety of methylcobalamin, alpha lipoic acid and pregabalin combination versus pregabalin monotherapy in improving pain and nerve conduction velocity in type 2 diabetes associated impaired peripheral neuropathic condition.
2013) Effectiveness of methylcobalamin and folinic Acid treatment on adaptive behavior in children with autistic disorder is related to glutathione redox status.
In contrast to methionine, methylcobalamin may be an effective methyl group donor, resulting in the efficient methylation (19%) of [iAs.
Cobalamin exists in two metabolically active forms, identified by alkali group attached to sixth coordinated position of cobalt atom: methylcobalamin and adenosylcobalamin.
First, methylcobalamin is a cofactor in the transformation of homocysteine to methionine.
In the cytosol, hydroxocobalamin can be methylated to methylcobalamin to convert homocysteine to methionine.
Effects of methylcobalamin on diabetic neuropathy," Clin Neurol Neurosurg, 94, 105-111, 1992.
Because superoxide, peroxynitrite, as well as advanced glycation end-products are formed in both microvasculature and neural tissues of the peripheral nervous system, methylcobalamin and pyridoxal 5'-phosphate are likely to act on multiple cell types.
53) Vitamin B12, in the form of methylcobalamin has been shown to lower homocysteine levels.
Fifty-seven children with autism spectrum disorder were randomly assigned to receive subcutaneous injections of methylcobalamin (75 pg per kg of body weight) or placebo (saline) every three days for eight weeks.
Cobalamin C (cblC) disease is the most common type of MMA and is characteristically concurrent with homocystinemia (HCY) due to impaired synthesis of two active forms of cbl, namely adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl).
These include B2 (riboflavin), feverfew, ginger, methylcobalamin, methylfolate, and magnesium.