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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 ?
For more about vitamin B12, refer to Jack Norris, RD's excellent webpage: Vitamin B12--Are You Getting It?
Cyanocobalamin is the most widely used form of vitamin B12, because of its stability and low cost, and because it can be converted in vivo to the biologically active forms of vitamin B12.
1 2014 Global Vitamin B12 (Cobalamin) Sales Market Share by Product Type
Although previous, smaller studies have evaluated the correlation between acid inhibitor use and B12 deficiency, this large-scale, longer-term analysis extends the results.
Vitamin B12 levels in the serum and cerebrospinal fluid in multiple sclerosis.
We cannot completely exclude residual confounding [factors besides the drugs] as an explanation for these findings, but, at minimum, the use of these medications identifies a population at higher risk of B12 deficiency, independent of additional risk factors," the authors (http://medicalxpress.
Among the 25,956 patients who had vitamin B12 deficiency, 12 percent used PPIs for at least two years, compared with 7.
It is important to quantify the magnitude of vitamin B12 deficiency," he said.
Although to my knowledge, vitamin B12 toxicity has not been reported, its extra benefit related to huge doses is also not known.
We get B12 from animal products--meats, fish, poultry, eggs, cheese, and yogurt, for instance--or from B12-fortified foods, notably breakfast cereals.
This longitudinal study adds to the literature by demonstrating a cause and effect relationship between OC use and serum B12 levels.
He has also received the Glory of India award for his work into vitamin B12 deficiency and has met Prime Minister David Cameron at 10 Downing Street.