ESTERASES

From Big Medical Encyclopedia

ESTERASES — the enzymes of a subclass of hydrolases (KF 3.1) catalyzing hydrolytic decomposition of ester groups and lactones. Picture of cytochemical distribution nek-ry E. in blast cells it is used as an accessory diagnostic character at differential diagnosis of various forms of leukoses (see). Increase in activity E. in urine observe at chronic nephrite (see), hron. renal failure and nephrotic syndrome. Activity of a ho-linesteraza (see) serves as additional diagnostic test at diagnosis of diseases of a liver, poisonings with organophosphorous connections in blood serum (see), at assessment of sensitivity of patients to Dithylinum (see).

Carry hydrolases of ethers to esterases carboxylic to - t (KF 3. 1. 1), the catalyzing reactions of RC(0)0R1 + H20=RC00H + RxOH where R and R1 is hydrocarbon radicals. Besides, also esterases of thiol ethers belong to a subclass of KF 3.1 (KF 3.1.2; glutathione-thiol-esterase, acetoacetyl Co A-gidrola-za, etc.), hydrolases of phosphoric monoesters, or phosphatases (KF 3. 1.3), hydrolases of phosphodiesters (KF 3.1.4; phospholipases of C and D, sfingomi-elin-phosphodiesterase, etc.), hydrolases of monoesters trifosforny to - t [KF 3. 1. 5; dezoksigtf (guanozintrifosfat) - an aza], hydrolases of ethers a chamois to - you are (KF 3.1.6) — sulphatases (see) and esterases of monoesters diphosphoric to - t (KF 3.1.7;


prenolpirofosfataz). Many from E. (cholinesterases, holesterinestera-for, lipases, nek-ry nonspecific E.) have transferazny activity (see Transferases), i.e. catalyze transfer of the acylic rest on other, than water, an acceptor.

AA. significantly differ among themselves on degree of water repellency of hydrolyzable substrates: so, substrates of cholinesterases are water-soluble connections, and lipases (see) are effective only on an interface of phases water — insoluble radio substrate. AA. on degree of inhibition organophosphorous connections divide on sensitive and insensitive. To insensitive E. sometimes mistakenly rank the enzymes capable to hydrolyze separate organophosphorous connections (a pas-raoksonazu, a zarinaza, a tabunaza and others).

AA., possessing wide substrate specificity (so-called nonspecific esterases), in a human body are especially active in a liver, kidneys and a small bowel where they are localized in a cytoplasmic reticulum, in lysosomes and, perhaps, in mitochondrions and cytoplasm. Maximum activity these E. show in the range of pH values from 5,0 to 8,0.

Karboksilesteraza (KF 3.1.1.1; the former name «ali-esterase») catalyzes preferential hydrolysis of aliphatic and aromatic ethers (see) the lowest monocarboxylic fatty acids (see), and also ethers milk, acetoacetic, amber, fumaric, the benzoic to - t and many amino acids. Optimum substrates for a karboksilesteraza are ethers with unpolar groups on both ends of a molecule. Enzyme hydrolyzes nek-ry cyclic connections (hydroxy butanole acid lactone, oksazolina, etc.) and practically does not hydrolyze ethers of sincaline. Karboksilesteraza has low sensitivity to Eserinum. Specific organophosphorous inhibitors of this enzyme are known (triortokrezilfosfat, etc.), however it is not sensitive to ions of tetraalkyl ammonium. The active center of a karboksilesteraza contains, apparently, the hydroxylic group of the rest of serine (see) activated by an imidazole of the rest of a histidine (see). Specificity of action of a karboksilesteraza and its difference from others E. are caused probably by existence in a molecule of enzyme at least of two hydrophobic sites responsible for binding of acylic and spirit parts of a molecule of substrate. The activating effect of substrate on enzyme is noted.

Arylesterase (KF 3.1.1.2) catalyzes hydrolysis various


348 AESTHETICS PRODUCTION

aromatic ethers. This enzyme was found for the first time in blood serum of the person, and then and in blood of other mammals on his ability to hydrolyze ethers of p-nitrophenol and (3 naphthols. Arileste-razu identify by means of specific substrates — phenyl-acetate and p-naftilpropionata. Aryl-esterase it is not sensitive to an inhibiting effect of organophosphorous connections and it is even capable to hydrolysis nek-ry of them. At an electrophoresis (see) blood sera activity of arylesterase is found in albuminous fraction. In blood serum of the person 12 fractions of arylesterase are revealed. Aryl-esterase, allocated from blood serum of the person, has transfe-different activity and catalyzes preferential transfer of the phenylic radical with korotkotsepochechny fat to - t on long chained, and the enzyme emitted from a liver of the person — on the contrary. Presumably function of arylesterase in a human body is connected with delivery in a liver long-chain fat to - t at hydrolysis of lipoproteids (see) in blood serum, a myocardium and lungs.

Acetyl from a teraz (KF 3.1.1.6; the atsetilgidrolaza of ethers acetic to - you) preferential catalyzes hydrolysis of aliphatic ethers acetic to - you. For the first time enzyme was emitted from a peel of orange. Catalytic properties acetyl of the esterase received from different sources are various: the enzyme emitted willows of kidneys of a dog has high affinity to ethers chloracetic to - you, and the enzyme received from a peel of orange catalyzes also hydrolysis of acetylcholine. Acetylesterase is not inhibited by organophosphorous connections and does not hydrolyze them, at presence p-hlormerkuribenzoata (reagent on sulphhydryl groups) activation of enzyme is observed.

Histochemical methods of detection of esterases in fabrics. By methods specific gistokhy. identifications E. in fabrics the method of simultaneous azocoupling, indigogen-ny reactions and, to a lesser extent, reactions with salts of heavy metals are (see. Histochemical methods of a research). As substrate at identification E. by method of simultaneous azocoupling apply (3-naftilatsetat, giving at coupling reaction with diazonium salts bright coloring. In Gomo-ri's modification as substrate use and-naftilatsetat. For identification E. by this method use frozen sections of the fabrics fixed during 10 — 16 hours in cold formalin (see). The structures having esterazny activity are painted in black color, and kernels — in dark blue. Lipases, acetylesterase and cholinesterase can give such coloring.

The methods based on indigo-gene reactions consist in enzymic hydrolysis of soluble esters of indoxyl (with release of free indoxyl) under the influence of fabric esterases. As substrates acetate, indoxyl-butyrate, the 5th bromine-4-chlorine-indoxyl-acetate and another replaced indoxyls use indoxyl. Cryostately cuts fix cold formalin and incubate in the environment containing ferricyanide and potassium ferrocyanide, buffered solution tris-HC1 (pH 6,8) and calcium chloride. Kernels dokrashivat hematoxylin or strong nuclear dye. The structures having esterazny activity are painted in turquoise color.

Indoksilatsetata karboksilesterazam of all types are hydrolyzed. Along with receiving blue indigotin as reaction product formation of the connection painted in red color was noted. Especially it is clear it is distinguishable at gistokhy. definition of esterazny activity in a brain; intensity of coloring increases at storage of drugs in a glycerin-@-Latina. Apparently, emergence of red coloring leaves formation of isatin during indigo-gene reactions.

Gistokhim. reactions with salts of heavy metals are based on use as substrate for esterases of oxyquinolinacetate, and as additional reagent — bismuth. In places of localization of esterazny activity the deposit of bismuth sulfide drops out. However this method has no particular advantages.

Bibliogrdikson M. and Webb E. Enzymes, the lane with English, M., 1982; Lloyd 3., Gossrau R. and Shiblert. A histochemistry of enzymes, Laboratory methods, the lane with English, M., 1982; Pearce E. A histochemistry, the lane with English, M., 1962; The nomenclature of enzymes, the lane with English, under the editorship of A. E. Braunstein, M., 1979;

Methods of enzymatic analysis, ed. by H. U. Bergmeyer, v. 2, p. 806, N. Y., 1974.

E. V. Rozengart; A. G. Ufimtsev and (gist.).

Яндекс.Метрика