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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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The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(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.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


vitamin B12
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In another study, researchers randomly assigned 95 people with debilitating fatigue and irritable bowel syndrome or inflammatory bowel disease to take vitamin B-12 (1,000 meg a day) or a placebo.
New evidence now indicates that if you're on this list, you may be at risk for a B-12 deficiency: 50 years or older (we can lose the ability to absorb vitamin B-12 as we age), vegetarian or vegan (B-12 is not found in plant foods), take metformin (a diabetes medication that can reduce the body's ability to absorb B-12), have any type of intestinal disorder or stomach surgery such as gastric bypass (vitamin B-12 needs a well-functioning gut to be absorbed), take anti-acid medicines or aspirin, ibuprofen or similar types of pain relievers (some meds can reduce the effectiveness of stomach acids to digest and absorb B-12).
Accordingly, the authors of the present study aimed to assess associations of niacin, folate, vitamin B-6, and vitamin B-12 intake in younger adulthood with cognitive function in midlife.
The greater intake of natural foods in the diet of participants with variant PKU was associated with greater intakes of vitamin D, vitamin B-12, iodine, selenium, and zinc compared to subjects with classical PKU [28].
She said the results don't tell them whether the high folate levels or high vitamin B-12 caused the autism risk, or whether certain genes led to the high folate levels and increased autism risk through some other mechanism.
Q: Should I be worried about a vitamin B-12 deficiency?
Hodgkin's X-ray crystallography unit at Oxford did the painstaking work, announced in 1955, to detect the structure of vitamin B-12. Her unit also worked on the chemical structure of the drug cephalosporin C, closely related to the penicillin family.
Taking folic acid and vitamin B-12 is sadly not going to prevent Alzheimer's disease.
Research has shown that supplements of vitamin B-12 and vitamin D can improve energy in people who are deficient in those nutrients.
Low vitamin B-12 concentrations in patients without anaemia: The effect of folic acid fortification of grain.
Poorer populations, however, usually suffer also from inadequate intakes of zinc, riboflavin, vitamin B-12, vitamin B-6, and calcium as they consume few animal products (meat, fish, poultry, eggs, or dairy products).
Rich in biotin, essential for cell growth, and vitamin B-12 they work wonders for hair inside and out.