Tryptophan

[Agnes]

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].

[Dianne]

An amino acid which is a constituent of most proteins. It is an essential nutrient in the diet of vertebrates.