CHOLINESTERASES

From Big Medical Encyclopedia

CHOLINESTERASES — the enzymes belonging to the class of hydrolases: atse-tilkholineeteraza (AHE; acetylcholine — an atsetilgidrolaza; synonym true cholinesterase; KF 3.1.1. 7) and cholinesterase (HE, BuHE; an atsilkho-lean — acylhydrolase; synonym: pseudo-cholinesterase, butirilkholinestera-for, etc.; KF 3. 1. 1. 8). Cholinesterases preferential catalyze hydrolysis of carboxylic ethers of sincaline (see): (CH3)3N+CH2CH20C(0)R + + H20 — (CH3)3N+CH2CH2OH +

+ RGOOH, where R — the hydrocarbon radical. Biol. the role of acetylcholinesterase consists in bystry hydrolytic decomposition of a neurotransmitter of acetylcholine (see) and participation thus in the course of neuromuscular transmission of nervous impulse (see. Nervous cell); function of other cholinesterases in a human body is definitely not established. Activity of cholinesterases in blood serum is an accessory diagnostic character of a number of diseases. The connections oppressing activity of cholinesterases (see Antikholinesterazny means), such as Galantaminum (see), about-zerin (see), physostigmine (see) etc., are used in medicine as pharmaceuticals at treatment of glaucoma, for the prevention and treatment of a postoperative atony of intestines, a bladder, for stimulation of patrimonial activity, at a myasthenia, etc.

Acetylcholinesterase contains in nervous tissue and in erythrocytes. Other cholinesterases are found in blood serum and a liver, in a mucous membrane of intestines, a pancreas.

For the first time activity of cholinesterase was found in 1926 in heart of a frog, and in 1932 enzyme was emitted from blood serum of a horse. In 40 — the 50th 20 century were established that high toxicity phosphorus of the organic compounds (see) having properties of neuroparalytic toxic agents (see) is caused by their inhibiting effect on cholinesterase, in a molecule a cut they phosphorylate the rest of serine (see), depriving thereby enzyme of an opportunity to contact substrate (see Phosphorylation). Carbamic connections (see) and Cholinomimetic substances belong to inhibitors of cholinesterases (see).

Acetylcholinesterase with the largest speed hydrolyzes acetylcholine, and also hydrolysis of acetyl-r-methylsincaline and an atset-oksietiliiperidiniya catalyzes. Cationic organophosphorous connections and an encore (Z-trimetilammony-5-gi a woadwaxen of Ife-noksi) - 1,3 pro-pan-diiodide (3116 ST)

are its inhibitors. Specific substrate butyrylsincaline-esterase is butyrylsincaline, inhibitors — diizopropilftor-phosphate, 10-(1 - dietilaminopropio-

Nile) a phenothiazinhydrochloride (ASTRA-1397).

Cholinesterases have fabric and specific specificity. They are simple proteins. The active surface of their molecule has the esterazny center of a catalysis and the anion center of binding which are framed with the hydrophobic areas defining specificity of enzyme concerning substrates and inhibitors. During the binding of substrate on an active center of enzyme its carbonyl group through system of hydrogen bindings forms a cycle with an imidazole of the rest of a histidine (see) and hydroxylic group of the rest of serine of the esterazny center of cholinesterase. Redistribution of electrons on this cycle leads to acylation of hydroxylic group of the rest of serine. Eliminating of acyl group proceeds with participation of water on the similar cyclic mechanism. Irreversible inhibition of cholinesterases organophosphorous connections reminds the mechanism of hydrolysis of substrate enzyme.

Definition of activity of cholinesterases is made by quantity of not hydrolyzed acetylcholine, a cut measured at action gidro-a ksilamin and FeCl3 ferric chloride with the subsequent fotometrirovaniye of Fe-atsetgidrokeamovy of a complex (Hestrin's method), and also on the shift of the size pH of incubatory mix resulting * from acidulation of the environment to - that, formed at hydrolysis of substrate (Mi person method and Molander's method — Friedman — the Castle); on measurement of amount of the thiosincaline which is formed at hydrolysis of acetylthiosincaline by means of chromogenic reagent 5,5 the '-dithiobis-2-nitrobenzoic to - you (Ellman's method).

Decrease of the activity of cholinesterase serves as an indicator of disturbance of beloksintezi-ruyushchy function of a liver in blood serum, it is observed also at bronchial asthma, rheumatic polyarthritis, a myocardial infarction, burns, traumatic shock, etc. At a thyrotoxicosis and nek-ry diseases of kidneys activity of cholinesterase in blood serum increases. Definition of activity of serumal cholinesterase is very important during the use of muscle relaxants (see) like a suktsinilkholin for providing an adequate anesthesia (see) since at nek-ry people it is revealed existence of the atipichesky cholinesterases incapable to hydrolyze this derivative sincaline that conducts to a so-called rekurarization, i.e. repeated oppression of a neuromuscular synapse after recovery of its function by the end of operation which is clinically shown a repeated relaxation and respiratory depression. One of actions for the prevention of this terrible complication is the timely dekurarization by administration of antikholinesterazny drugs.

Reaktivatora of cholinesterases. The antagonists of organophosphorous connections capable to recover activity of cholinesterases by dephosphorylation of a molecule of the inactivated enzyme received the name of reaktivator of cholinesterases. At chemical structure of all reaktivator of cholinesterases there is ok-simnaya a group (-NOH), edges is responsible for reactivation of enzyme therefore these connections often for brevity are called just oximes. The oximes containing quarternary onium groups belong to reaktivator of cholinesterases (pralidoksimyodid — 2-PAM, pra-lidoksimkhlorid, to protons — P2S, dipiroksy. Trimedoximum — TMB-4, toksogonin, etc.), and oximes, free of quarternary onium groups (monoizonitrozoatseton — the MINE, Isonitrosinum, dietiksy, etc.).

On character of the pharmakol. actions reaktivator of cholinesterases are antidotes (see Antidotes of OV) the organophosphorous connections having anti-sincaline-esteraznym effect. Recovering activity of cholinesterases in bodies, function to-rykh was broken as a result of the termination of hydrolysis of synoptic acetylcholine, reak-tivator of cholinesterases promote recovery of synoptic transfer to the level compatible to life. It was established that during creation in an organism of sufficient concentration of reaktivator of cholinesterases the neuromuscular block called by oppression of cholinesterase was removed bradycardia decreased, breath was recovered, others disappeared pathogenetic the significant disturbances arising at poisoning with organophosphorous connections.

Reaktivatora of cholinesterases are capable to recover activity both butyrylcholinesterases, and acetylcholinesterases, however therapeutic value has only recovery of activity of acetylcholinesterase as the enzyme responsible for hydrolysis of synoptic acetylcholine.

Depending on expressiveness of the central and peripheral effects reaktivator of cholinesterases divide into two groups: preferential peripheral action and the mixed action (central and peripheral). Mono concern to the first - and bischetvertichny oximes, to-rye because of low lipophilicity badly get through a blood-brain barrier (see) and therefore do not reactivate or in insignificant degree reactivate acetylcholinesterase of a brain. Tertiary oximes easily get through gistogematichesky barriers and equally reactivate cholinesterase of a brain and peripheral nerve terminations, being, thus, reaktivator of the mixed action. Sometimes they are called reaktivator of cholinesterases of the central action, emphasizing with it their difference from reaktivator only of peripheral action.

The biochemical mechanism of action of reaktivator of cholinesterases is based on interaction of a molecule of an oxime with fosforilirovanny enzyme. This process presumably can proceed in two stages. At the first stage the reaktivator contacts fosforilirovanny group of inhibited enzyme, at the second stage consolidation of this communication results from nucleophilic attack by an oxime of atom of phosphorus that leads to a rupture of a covalent bond between fosforilny group and enzyme and to recovery of its activity. Process of reactivation of cholinesterase happens according to the following equation: And“ + <НЕР±А • HEP-*HE+ + ARE,

where And" — anion of an oxime, NER — fosforilirovanny enzyme,

A-HEP — a complex of an oxime with fosforilirovanny enzyme, NOT — active enzyme, ARE — a complex of fosforilny group with an oxime. At interaction with fosforilirovanny cholinesterase of tertiary oximes, napr, Isonitrosinum, formation of a complex happens without preliminary linkng of an oxime with fosforilirovanny enzyme at the expense of hydrogen bindings or van-der-vaalsovykh of forces (see the Molecule). At use of quarternary oximes as reaktivator of cholinesterases stronger communication of an oxime with enzyme since at first it is occluded on a molecule of enzyme due to positive charge of quarternary nitrogen of an oxime and a negative charge of the anion center of enzyme is reached. Not accidentally the most active reaktivator of cholinesterases are quaternary compounds though recently quite active reaktivator and among connections, free of onium group are found (derivatives oksoimino-acetum, ketohydroxymova to - t, etc.).

Among the factors influencing activity of reaktivator of cholinesterases, degree of anchoring strength of organophosphorous connection with cholinesterase and speed of loss by enzyme of ability to reactivation (so-called aging of enzyme) has the greatest value. Both of these factors caused by structure of inhibitor define an opportunity and extent of reactivation of enzyme. E.g., the GD used by nek-ry foreign researchers as inhibitor of cholinesterases forms difficult reactivated complex with enzyme. There is a possibility of competitive delay of quickly proceeding process of aging of enzyme in the presence of nek-ry reaktivator of cholinesterases in sufficient concentration. Believe that in this respect bischetvertichny piridi-niyevy connections (e.g., drug toksogonin) are more active, than monoquarternary. Efficiency of reaktivator of cholinesterases concerning physostigmine, sevin and other carbamates is doubtful because of insufficiently expressed ability of oximes to a dekarbamoilirovaniye of cholinesterases. There are data that to reactivate cholinesterases, inhibited connections like an ambenonium chloride (see), to-rye are not carbamates, it is practically not possible. The antidotal effect of oximes can consist not only of reactivation of cholinesterases, but also of their direct chemical interaction with organophosphorous connections. However this antidotal action of oximes can be shown only on condition of preliminary interaction of reaktivator of cholinesterases with organophosphorous connections. Believe that composed antidotal effect of nek-ry bischet-vertichny piridiiiyevy connections are their cholinolytic (ganglioblokiruyushchy, kurarepodob-ny) properties. Nevertheless there are no authentic proofs that pharmakol. activity of the listed types of reaktivator of cholinesterases plays a role in formation of their antidotal effect in such measure that it was possible to call into question the developed ideas of the mechanism of action of these connections.

The only indication to a wedge, to use of reaktivator of cholinesterases is acute poisoning organophosphorous anti-sincaline-esteraznymi substances. Preferably whenever possible early intravenous administration of massive doses of the substances reactivating cholinesterases since at the same time the best conditions for interaction of an antidote with the cholinesterase inactivated by phosphorylation are created (that does not exclude use of these connections in later terms). In the latter case notable recovery of activity of enzyme can be reached though not so considerable, but nevertheless that can be decisive in struggle for life of the victim. Antidotal efficiency of reaktivator of cholinesterases can be increased by a combination of oximes of multidirectional action (e.g., a combination of a dipiroksim to Isonitrosinum).

Specific therapy by reaktivator of cholinesterases is carried out under constant control of activity of cholinesterase in blood serum (see Dipiroksim). Recovery of activity of enzyme for 20 — 40% is considered a favorable predictive sign. At overdose of reaktivator side effects (moderate decrease in the ABP, tachycardia) can be shown, to-rye usually pass with drug withdrawal.

As reactivation of enzyme in the conditions of acute poisoning happens much more slowly, than accrue life-threatening symptoms, therapy by reaktivator of cholinesterase it is necessary to carry out against the background of intensive atropinization (2 — 3 ml of 0,1% of solution of atropine for each introduction of a reaktivator of the cholinesterase) providing quickly coming protection of holino-receptors against excessive cholinergic excitement. It allows to win time necessary for increase in activity of enzyme to therapeutic significant sizes.

See also Poisonings, the table.

Cholinesterases in the medicolegal relation. The research of activity of cholinesterases is used in forensic medicine for diagnosis of poisonings with antikholineste-different substances: at hit in an organism in quantity even of 2 — 3 lethal doses these poisons in not changed look, as a rule, do not remain since they are completely spent for reaction with cholinesterase.

At court. - chemical definition of activity of cholinesterases in fabrics estimate the speed of enzymic hydrolysis of substrate (acetylcholine) which is previously added to incubatory test. Under certain conditions (temperature, pH of the environment, etc.) the speed of hydrolysis of acetylcholine is constant. After addition of the inactivator (e.g., trichloroacetic to - you) the quantity remained not destroyed substrate is defined biol. or biochemical ways.

In court. - medical practice use also gistokhy. methods of detection of activity of cholinesterases. As postmortem changes (see) within the first three days after death exert insignificant impact on activity of cholinesterases in fabrics, its subnormality is of great importance in court. - medical diagnosis of poisonings to an antikholinesta different substances. At the same time not only the fact of decrease in the general activity of cholinesterases is considered, but also change of this activity in various fabrics is compared that allows to define type of the antikholinesterazny substance which caused poisoning (see). Nek-rye from such substances (Phosphacolum, isomercaptophos, etc.) equally is oppressed activity of cholinesterases in various bodies and fabrics, other antikholinesterazny substances (Arminum, etc.) preferential oppress activity of cholinesterase in a brain, the third (octamethyl, etc.) — preferential inhibit cholinesterases in peripheral fabrics.

Researches of cholinesterases are conducted sometimes at establishment of motherhood, paternity and replacement of children (see Motherhood a disputable, doubtful paternity). At the same time detection of extremely rare atypical form of cholinesterase is of great importance.


Bibliography: About l and to about in S. N. and 3 and at -

about l N and to about in S. D. Reaktivatora of cholinesterases, L., 1970, bibliogr.; About l and-kovs.n. and Rozengartv. I. Cholinesterases and antikholinesterazny substances, L., 1964, bibliogr.; Luzhniki E. A. Clinical toxicology, page 306, M., 1982; Rozengartv. I. Holin

of esterase, the Functional role and clinical value, in book: Probl. medical chemical, under the editorship of V. S. Shapot and E. G. Larsky, page 66, M., 1973; With m at with and Ya. S N. Forensic medical examination of poisonings anti-holinesteraznymi substances, M., 1968, bibliogr.; T about m and l and V. V. N and of l and recreation center and x A. S. A medicolegal blood analysis in cases of a doubtful paternity, motherhood and replacement of children, M., 1981; Cholinesterases, the Active center and the mechanism of action, under the editorship of X. Hamidova, Tashkent, 1976, bibliogr.; Bosk about vie B., MaksimovicM.a.MiniD. Ageing and reaktivation of acetyl cholinesterase inhibited with soman and its thiocholine-like analog, Biochem. Pharmacol., v. 17, p. 1738, 1968; Handbuch der experi-mentellen Pharmakologie, hrsg. v. A. Heffter, Bd 15, B., 1963; Neurobiology of cholinergic and adrenergic transmitters, ed. by B. Heldman a. o., v. 7, p. 85, Basel a. o., 1980.

E. V. Rozengart; C.H. Golikov (reaktivator of cholinesterases), R. V. Berezhnaya (court.).

Яндекс.Метрика