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nicotinic acid: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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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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(also niacin, vitamin PP [pellagra-preventive factor], or 3-pyridinecarboxylic acid), a water-soluble vitamin of the B complex. It forms colorless crystals with a melting point of 234°-237°C. Its structural formula is
Nicotinic acid is widespread in living organisms. Yeast, wheat bran, meat, and especially liver and kidneys contain the richest concentration of the vitamin. The nicotinic acid amide—nicotinamide—a constituent of the important coenzymes NAD and NADP, also possesses vitamin activity.
Symbiotic bacteria, chiefly from the intestinal flora, and many animals synthesize nicotinic acid from tryptophan. In rats, mice, and man, tryptophan is converted to nicotinic acid partially by the activity of the intestinal microflora but mainly in the liver. The role of nicotinic acid in the body is to maintain the normal condition of the epidermis, of the epithelium of the alimentary canal, and nervous system function. The vitamin does so by participating as a constituent of coenzymes in many enzymatic processes.
The daily nicotinic acid requirement of man is about 20 mg. A deficiency of nicotinic acid results in pellagra. As a vitamin preparation, nicotinic acid is used as a specific agent in the treatment of several pathological conditions, including pellagra, gastrointestinal diseases, liver disorders, vascular spasm, and atherosclerosis.