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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 ?
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.
The recommended daily allowance for vitamin B-12 in healthy adults is 2.
The company said that by making it easy to obtain these services in its retail locations with no appointment necessary, it hopes to help seniors and other patients who have B-12 deficiency and also young women and men who want to lower their risk for serious disease caused by HPV.
We're using the vitamin B-12 drug to treat dogs that have cancer.
High levels of homocysteine are associated with dysfunction of the blood vessel linings, whereas treatment with vitamin B-6, vitamin B-12 and folic acid appears to reduce homocysteine levels and may reverse this blood vessel dysfunction.
It is recommended to add B-12 when taking high doses of B-9; they can hide B-12 insufficiency.
If high folic acid aggravates vitamin B-12 deficiency what should be done about it?
An inability to absorb vitamin B-12 properly causes pernicious anemia, leading to fatigue and neurological complications.
Now in a newly updated and expanded fourth edition, Simply Vegan: Quick Vegetarian Meals includes information about Protein, Fat, Calcium, Iron, Vitamin B-12, Sources of Omega-3 Fats, Weight Loss, and more.
Some people report relief from vision problems after taking vitamin B-12 shots.
In a recent study published in the Journal of Nutrition, researchers monitored the dietary practice of pregnant women and its effect on serum vitamin B-12 concentrations.
Levels are kept at a healthy minimum by ensuring that your diet contains sufficient amounts of vitamins B-9 (folic acid), B-12 and B-6, maintaining a healthy body weight, remaining physically active, eating plenty of fiber, managing hypertension and limiting alcohol consumption.