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tryptophan

tryptophan (trĬp´təfăn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. It is one of several essential amino acids needed in the diet; human beings cannot synthesize it from simpler metabolites. Young adults require about 7 mg of this amino acid per day per kg (3 mg per lb) of body weight. Nicotinic acid (niacin), a vitamin of the B complex, can be made from tryptophan in the body, but evidently the rate of transformation is insufficient for the demands of normal growth and maintenance, and hence nicotinic acid must be supplied in the diet. Deficiency of tryptophan in the diet enhances the progress of the vitamin-deficiency disease pellagra, which is treated by restoring nicotinic acid to the diet, usually supplemented with tryptophan. Bacteria in the intestine break tryptophan down to compounds such as skatole and indole, which to a great extent are responsible for the unpleasant odor of feces. Tryptophan contributes to the structure of proteins into which it has been incorporated by the tendency of its side chain to participate in hydrophobic interactions (see isoleucine). The amino acid was isolated from casein (milk protein) in 1901, and its structure was established in 1907.

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tryptophan

tryptophan An essential amino acid. In addition to its role in protein synthesis, it is the precursor of the neurotransmitter 5‐hydroxytryptamine (serotonin) and of niacin. Average intakes of tryptophan are more than adequate to meet niacin requirements without the need for any preformed niacin in the diet.

It is destroyed by acid, and therefore not measured when proteins are hydrolysed by acid before analysis; determination of tryptophan requires alkaline or enzymic hydrolysis of the protein.

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tryptophan

tryptophan (trip-tŏ-fan) n. an essential amino acid. See also amino acid.

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tryptophan

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tryptophan

tryptophan A heterocyclic, non-polar, alpha amino acid.

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tryptophan

tryptophan See amino acid.

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