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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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, 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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A vitamin, widespread in nature. It is only sparingly soluble in water; it is stable in boiling water solutions, but can be destroyed by oxidizing agents, acids, and alkalies. Under some conditions, it can be destroyed by oxidation in the presence of rancid fats. Biotin's occurrence in nature is so widespread that it is difficult to prepare a natural deficient diet. Biotin deficiency in animals is associated with dermatitis, loss of hair, muscle incoordination and paralysis, and reproductive disturbances. Biotin deficiency produced in humans by feeding large amounts of egg white resulted in dermatitis, nausea, depression, muscle pains, anemia, and a large increase in serum cholesterol. See Coenzyme
(vitamin H), a water-soluble vitamin contained in yeasts and other microorganisms, and also in liver, egg yolk, kidneys, milk, cauliflower, and other vegetable products. The daily requirement of humans for biotin (0.25 mg) is usually provided by the microflora of the intestinal tract; it is therefore unnecessary to introduce it in the diet. Biotin has been obtained synthetically.
Avitaminosis H may be produced in laboratory animals by feeding large quantities of raw egg white, which contains a biotin antagonist, avidin, which decomposes when heated to 100° C. Affection of the skin of the seborrheic type is observed in avitaminosis H. Biotin is a coenzyme and participates in the transfer of carbon dioxide gas and its fixation in biosynthesis; its other functions have not been clarified.