TYROSINE

From Big Medical Encyclopedia

TYROSINE — alpha amino - beta (n-oxyphenyl) - propionic acid, C 9 H 11 NO 3  ; is replaceable aromatic monoamino-monocarboxylic acid. T. it is necessary for life activity of a human body and animals since is molecular composition of proteins (see), including enzymes (see), serves as the biosynthetic predecessor of catecholamines (see) — dioxyphenylalanine (see), dopamine, adrenaline (see), noradrenaline (see), melanin (see), thyroxine (see), a shooting gallery of amine (see), and also many proteinaceous and peptide hormones (see), in particular hormones of a thyroid gland of thyroxine and triiodothyronine (see), being the iodated component (see Yodtirozina, Yodtironina) specific protein of a thyroid gland of thyreoglobulin (see). In plants of T. participates in synthesis of alkaloids (see) — morphine (see), codeine (see), a papaverine (see), colchicine. Insufficiency of T. in an organism leads to disturbance of protein synthesis, catecholamines, etc. Disturbance of exchange of T. find at diseases of a liver and kidneys, alcoholism, rheumatism, a melanoma, and also at such hereditary diseases as a tyrosinosis (see), an alkaptonuria (see), albinism (see).

T. 10 were for the first time allocated. Libikh in 1846. Maintenance of T. (as a percentage) makes in insulin (see) and ribonucleases (see) cattle 12,6 and 7,6 respectively, in cytochrome with (see Tsitokhroma) horses — 4,9, hemoglobin (see) the person — 2,9, a myoglobin of the person (see the Myoglobin) — 2,4, fibroin of silk and albumine (see) — 11 — 13. In blood serum of the person concentration free T. it is equal to 1,5 — 2,2 mg / 100 to ml (15 — 22 mg/l)] with urine from 15 to 50 mg of T. V are allocated per day to a molecule of hemoglobin the remains of T. in situation 140 and 145 binding of oxygen, replacement of T provide., napr, on histidine (see), deprives hemoglobin of this property. Lactoperoxidase of milk in the presence of iodine (see) and hydrogen peroxide catalyzes reaction of iodination of the rest of T. in proteins: covalent modification of T. in structure of proteins, enzymes, hormones leads to change of physiological activity of these substances.

Pier. weight (weight) of T. makes 181,2. Not loaded polar IT is group of phenol in a molecule T., edges at pH 7,0 it is poorly ionized, capable to form hydrogen bindings with water molecules and to contact effectively other molecules having a flat configuration. An isoelectric point (see) T. is at pH 5,65. Absorption spectrum of solutions T. has maksimukhm at the wavelength of 278 nanometers. In live organisms there is only an alpha tyrosine. Allocated from biol. objects L-tyrosine represents silky acicular crystals; relative density at 25 ° is equal to 1,456; specific rotation [a]20 = — 8,64; t°pl 290 — 295 ° (with decomposition at simmer) and 314 — 318 ° (with decomposition at bystry heating). Solubility (in / 100 ml) in water at 25 ° — 0,048., at 75 ° — 0,238, in ethanol at 17 ° — 0,01, in ether T. it is insoluble. D-tyrosine represents colourless crystals; [a] 20 = +8,64; t°pl 310 — 314 °. DL tyrosine (racemic substance) — brilliant acicular crystals with t°pl 290 — 295 (with decomposition at simmer) and 340 ° (with decomposition at bystry heating); water solubility at 20 ° — 0,041, DL tyrosine in ethanol and ether is insoluble.

In a human body and animals L-tyrosine is formed as a result of an irreversible hydroxylation of the phenylalanine (see) catalyzed by system of a phenylalanine-4-hydroxylase (KF 1.14.16.1) and also arrives with vegetable and animal protein of food. T. it is used for biosynthesis of proteins, in information RNA (see. RNA ) it is coded by two codons: UAU and UATs (see. Genetic code ).

In a liver at disintegration of T. its alpha amino group turns into ammonium nitrogen and is brought out of an organism in the form of azo compounds (see), and in reactions of transamination (see) is transferred to alpha ketoglutarate with the subsequent formation of products of a nitrogen metabolism (see). During the rotting and under the influence of a bacterial flora of intestines in the course of deamination (see) and disintegration of side chains from T. n-oksifenilpropionat, n-oksifenilatsetat, cresols, phenol are consistently formed.

Receive T. from hydrolyzates state (see), proteins of soy and other, rich T. sources, and also by chemical synthesis.

For qualitative and semi-quantitative test of T. in biol. material apply methods of a chromatography (see) on paper, and to exact quantitative definition — flyuorimetrichesky (see Flyuorimetriya), electrophoretic (see. Electrophoresis ) methods and ion-exchange chromatography in the aminoacid analyzer.

Bibliography: Berezov T. T. and Korovkin B. F. Biological chemistry, M., 1982; Rapoport S. M. Medical biochemistry, the lane with it., page 54, M., 1966; Whyte A., etc. Fundamentals of biochemistry, the lane with English, t. 1 — 3, M., 1981.


A. M. Shaposhnikov.

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