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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 ?
Patients receiving B-12 injections at MinuteClinic must be over 18 years old and present a prescription for the injections or have a prescription on file with the pharmacy.
Vitamin B-12 deficiency is the dominant nutritional cause of hyperhomocysteinemia in a folic acid-fortified population.
The new test involves drinking a small amount of vitamin B-12 labeled with radioactive carbon 14 (14C) and collecting a single drop of blood.
They observed that the statistical relevance of both vitamin B-12 intake and weight loss after three months was diminished after a six-month period.
Vitamin B-12 is found in all foods of animal origin including eggs and dairy products, and an adequate intake of vitamin B-12 is generally not a concern for vegetarians who eat some dairy products or eggs.
British scientists randomly assigned roughly 200 people aged 75 or older who had moderate vitamin B-12 deficiency to take either B-12 (1,000 micrograms a day) or a placebo.
In that elevated homocysteine is associated with cognitive impairment, Robert Clarke of from the University of Oxford (Oxford, UK) and colleagues investigated whether vitamin B-12 could effectively reduce the occurrence of dementia.
The gum comes in spearmint and cinnamon flavors, and includes a dose of vitamin B-12 for that extra kick start in the morning.
The increase in production was due to Eugene Island 339 B-12 well coming online in July of 2006 and the completion of the gas injection project on the Eugene Island 339 B-5 well.
Sealed Electronic Bid: B-12 control structure repairs
The women were given high doses of the B vitamin folic acid (2,500 micrograms a day), vitamin B-6 (50 milligrams a day), and vitamin B-12 (1,000 mcg a day), or a placebo.
The study discovered that B vitamins, including B-6, B-12 and folic acid, slow down mild cognitive impairment (MCI), a condition which is a major risk factor for Alzheimer disease and other forms of dementia.