choline(redirected from transmethylation factor)
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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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A compound, trimethyl-β-hydroxyethylammonium hydroxide, used by the animal organism as a precursor of acetylcholine and as a source of methyl groups. It is a strongly basic hygroscopic substance with the formula
Choline deficiency in animals is associated with fatty livers, poor growth, and renal lesions. It is a lipotropic agent. There is no direct evidence of disease in humans due to choline deficiency, although there have been suggestions that some of the liver, kidney, or pancreas pathology seen in various nutritional deficiency states may be related to choline insufficiency. Choline is found in acetylcholine, which is necessary for nerve impulse propagation, and in phospholipids.
Humans eat 50–600 mg of choline per day, but only excrete 2–4 mg. Thus, conventional tests are of no value in studying choline requirements, and no knowledge of human choline requirements exists. See Acetylcholine
(also 2-hydroxyethyltrimethylammonium hydroxide), [(CH3)3N+CH2CH2OH]OH–; occurs as colorless crystals. Choline is readily soluble in water and ethyl alcohol but is insoluble in ether and benzene. It easily forms salts with strong acids, and in aqueous solution it possesses the properties of a strong base.
Choline was first obtained from bile. Widespread in living organisms, it is particularly abundant in egg yolk and in the brain, liver, kidneys, and heart muscles of animals. It is usually regarded as a vitamin of the B complex, although animals and microorganisms are able to synthesize it. Choline is a constituent of phospholipids, such as lecithin and sphingomyelin, and it functions as a donor of methyl groups in the synthesis of methionine. From choline, animals can synthesize acetylcholine, which is one of the most important transmitters of nerve impulses. Choline is a lipotropic agent—that is, it prevents serious liver disorders that may arise as a result of excess accumulations of fat in the liver.
Choline chloride is used in medicine for the treatment of liver diseases and is included in some animal feeds. It is used for analytical purposes because of its ability to form poorly soluble salts with phosphotungstic acid, chloroplatinic acid, and certain other heteropoly acids.
V. A. IAKOVLEV