TYROSINASE

From Big Medical Encyclopedia

TYROSINASE (monophenol, digidroksifenilalaniya: oxygen oxidoreductase, KF 1.14.18.1; synonym: monophenol-monooxygenase, orthophenolase, katekholoksidaza, polifenoloksidaza, laccase; o-and n-difenoloksidaza, orthophenolase, an urushiol-oxidase) — the enzyme belonging to the class of oxidoreductases and catalyzing reaction between two hydrogen donators with inclusion of oxygen atom from O 2 in a molecule of one of them. T. treats metalloproteins (see) and is the only enzyme in a human body, animals and at plants, catalyzing multistep reaction of transformation tyrosine (see) in melanina (see) in the presence of oxygen according to the scheme: tyrosine -> 3,4 dioxyphenylalanine (see. Dioksifenilalanin ) —> phenylalanine-3,4-quinone -> a 2-carboxy-2,3-dihydro-5,6-dioxyindole —> indole-5,6-quinone -> melanin. The mechanism of the catalyzed T. reactions differs in one unique feature: the intermediate product of reaction serves as a reducer for ions of Cu2 + (see. Copper ), what is followed by formation of quinone (see Quinones), polymerization to-rogo leads to an end product of reaction — to melanin. From activity of T. in many respects skin color depends. Falloff of activity of T. or the block of its synthesis in melanocytes caused a hereditary disease albinism (see).

At animals and the person T. it is localized in cytoplasmatic organellas of melanocytes (the special cells synthesizing melanin) — melanosoma.

T. it was for the first time allocated from mushrooms, then it is received from juice of the Japanese varnish tree. It contains also in other plants and causes darkening of the broken fruit.

T. from mushrooms of Polyporus has a pier. the weight (weight) 120 000, consists of 4 subunits, each of to-rykh contains 1 atom of copper. This T. it is not sensitive to action of a karboksid (SO carbon oxide). T. contains three types of copper ions: one type of blue color, connects 02, other type of ions which is not painted in blue color serves as the center of binding of anions, the third — forms diamagnetic couple, edges serves as the two-electronic acceptor receiving electrons from substrate of enzymatic reaction and then transferring them on 02. The tyrosinase allocated from a melanoma of a hamster has an optimum of action at pH 6,8. Multiple forms T. (see. Isoenzymes ) are found in extracts from fabric of melanomas of various mammals, including and the person, and also in skin and hair bulbs of the pigmented mice. Melanotsitostimuliruyushchy hormone (see) activates T. also induces education premelanosy. Inhibitors T. cyanide and diethyldithiocarbamate, to-rye in a molecule T are. connect copper ions and reduce activity of enzyme by 50 — 65%, and also other connections forming complexes with copper.

Methods of determination of T. are based on spektrofotometrichesky quantitative measurement (see. Spektrofotometriya ) the painted reaction products (DOFA-chrome, DOFA-quinone) or on manometrical measurement of speed of consumption 02 with use as DOFA substrate. Activity unit of T., determined by this method, it is equal 1 mkl consumed 02 in 1 min. at 37 ° at pH 6,8. T. receive by fractionation on DEAE-cellulose.



Bibliography: Berezov T. T. and Korovkin B. F. Biological chemistry, M., 1982; M e c of l e r D. Biokhimiya, the lane with English, t. 1 — 3, M., 1980; The Nomenclature of enzymes, the lane with English, under the editorship of A. E. Braunstein, M., 1979; Whyte A., etc. Fundamentals of biochemistry, the lane with English, t of i — 3f m, 1981.


A. M. Shaposhnikov.

Яндекс.Метрика