Biotin

A water-soluble B-complex vitamin involved in carbon dioxide transfer and therefore essential to the metabolism of carbohydrate and fat. A balanced diet usually contains enough biotin. Foods with high biotin levels include nuts, cereals, green leafy vegetables and milk. Biotin deficiency, which is characterized by hair loss and a scaly red rash, can occur with prolonged intravenous feeding or the frequent consumption of raw egg whites which contain a biotin antagonist called avidin. Biotin supplementation is recommended during pregnancy because the biotin requirement rises during pregnancy and a substantial number of pregnant women become biotin depleted. Extra biotin is also needed during long-term anticonvulsant treatment which depletes biotin.

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The d-isomer component of the vitamin B₂ complex occurring in or required by most organisms and inactivated by avidin; participates in biologic carboxylations. It is a small molecule with a high affinity for avidin that can be readily coupled to a previously labeled antibody in order to allow visualization by enzymatic or histochemical means. SEE ALSO: avidin. SYN: coenzyme R, vitamin H, W factor.

- b. carboxylase a subunit of a number of enzymes ( E.G., acetyl-CoA carboxylase). It catalyzes the formation of carboxybiotin (on a b. carrier protein), ADP, and P_i from ATP, CO₂ and b..

- b. oxidase an enzyme (probably nonspecific) catalyzing the beta-oxidation of the b. side chain.

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bi·o·tin 'bī-ət-ən n a colorless crystalline growth vitamin C₁₀H₁₆N₂O₃S of the vitamin B complex found esp. in yeast, liver, and egg yolk called also vitamin H

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n.

a vitamin of the B complex that is essential for the metabolism of fat, being involved in fatty acid synthesis and gluconeogenesis. A biotin deficiency is extremely rare in humans; it can be induced by eating large quantities of raw egg white, which contains a protein - avidin - that combines with biotin, making it unavailable to the body. Rich sources of the vitamin are egg yolk and liver.

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bio·tin (biґo-tin) 1.a water-soluble dicyclic monocarboxylic acid considered to be part of the vitamin B complex; it is an essential cofactor for several carboxylases, plays a role in the metabolism of fatty acids and the deamination of certain amino acids, and is also used in vitro in biochemical assays based on biotinylation (q.v.) of various molecules. Deficiencies in humans have occurred only after prolonged total parenteral nutrition not supplemented with biotin or on ingestion of large quantities of raw egg whites (see avidin); manifestations have included dermatologic, neurologic, and ocular disorders. In some animals, deficiency has resulted in graying and loss of hair. [USP] 2.a preparation of biotin, used as a nutritional supplement.