..... Click the link for more information. 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 vitamin, 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
..... Click the link for more information. 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 pellagra , deficiency disease due to a lack of niacin (nicotinic acid), one of the components of the B complex vitamins in the diet. Niacin is plentiful in yeast, organ meats, peanuts, and wheat germ.
..... Click the link for more information. , 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 isoleucine , organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
..... Click the link for more information. ). The amino acid was isolated from casein (milk protein) in 1901, and its structure was established in 1907.
tryptophan
One of the essential amino acids. It is a heterocyclic compound that is found in small amounts in most proteins. It plays an important role in the growth and development of infants and in the biosynthesis of serotonin and niacin (thus, deficiency of niacin or tryptophan can cause pellagra). Its occurrence in milk has been suggested as the reason that drinking milk before bedtime helps people sleep. It is used in medicine and nutrition research, in enriched foods, and as a dietary supplement.
tryptophan [′trip·tə‚fan]
Tryptophan
β-(β-indolyl)-α-aminopropionic acid, one of the most important natural amino acids. It exists in the form of optically active L- and D- forms and a racemic DL-form. L-tryptophan is a minor constituent of gamma globulins, fibrinogen, casein, and other proteins.
L-tryptophan is an essential amino acid. The daily requirements for adults and children up to seven years of age are 0.25 g and about 1 g, respectively. Tryptophan is synthesized in microorganisms and plants by condensation of the amino acid serine with indole, which is catalyzed by the enzyme tryptophan synthetase. (The biosynthesis of tryptophan in E. coli was used to demonstrate the collinearity of a gene and the polypeptide chain coded by that gene, in which the position of each amino acid in the polypeptide chain is determined by a special portion of the gene.) L-tryptophan undergoes complex transformations in animals, forming a number of essential compounds: its decomposition products are the basis for the formation of nicotinic acid and serotonin in humans and other mammals, eye pigments (ommo-chromes) in insects, and heteroauxins, indigo, and several alkaloids in plants. Skatole and indole are formed from tryptophan during putrefactive processes in the intestine. During the normal breakdown in the body, six of the 11 carbon atoms of tryptophan are included in the Krebs cycle through acetyl and acetoacetyl coenzyme A, and the other five are converted to CO2.
In humans, the congenital absence of tryptophan pyrrolase, the enzyme that oxidizes tryptophan, results in feeblemindedness. Disruption of tryptophan metabolism in humans may be indicative of several serious diseases, including tuberculosis, cancer, and diabetes. Functional and organic disorders may also be caused by an insufficiency of tryptophan in the human diet and animal feed, resulting from the low content of tryptophan in many natural proteins. The food value of many proteins can be increased through the addition of synthetic tryptophan, obtained by chemical synthesis from acrylonitrile, ammonia, hydrogen cyanide, or phenylhydrazine. Techniques for enzymic synthesis of tryptophan from indole, pyruvic acid, and ammonia are under development.
REFERENCES
Braunshtein, A. E. Biokhimiia aminokislotnogo obmena. Moscow, 1949.Lehninger, A. Biokhimiia. Moscow, 1974. (Translated from English.)
Meister, A. Biokhimiia aminokislot. Moscow, 1961. (Translated from English.)
Safonova, E. N., and V. M. Belikov. “Uspekhi v oblasti sinteza i proizvodstva a-aminokislot.” Uspekhi khimii, 1974, vol. 43, no. 9.
E. N. SAFONOVA
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