Cholinesterase


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Related to Cholinesterase: acetylcholine, cholinesterase test, Cholinesterase enzyme, Cholinesterase inhibitors

cholinesterase

[′kō·lə′nes·tə‚rās]
(biochemistry)
An enzyme found in blood and in various other tissues that catalyzes hydrolysis of choline esters, including acetylcholine. Abbreviated chE.

Cholinesterase

 

any of a group of enzymes of the hydrolase class that act as a catalyst in the hydrolysis of choline esters, according to the equation

(CH3)3N + CH2CH2OCOR + H2O → (CH3)3N+ CH2CH2OH + RCOOH

The cholinesterase of the greatest biological importance is that of the nervous system, acetylcholinesterase (ACE), which acts as a catalyst mainly for the hydrolysis of acetylcholine (R = CH3). Cholinesterases that hydrolyze predominately the esters of choline and other carboxylic acids, such as propionic and butyric acid, have retained the trivial name cholinesterase.

ACE catalyzes the hydrolysis of acetylcholine to acetic acid and choline. Acetylcholine, a highly active substance, is secreted in the synapses of the nervous system and takes part in the transmission of nerve impulses from one nerve cell to the next and from nerve cells to the appropriate organs, such as muscles and endocrine glands. It must be rapidly broken down, however, because accumulations of it block the transmission of nerve impulses and cause paralysis—that is, the loss of nerve functions. For this reason, substances that suppress ACE activity are highly toxic; such substances include organophosphate insecticides, physostigmine, and proserine.

An enzyme with properties similar to those of ACE is found in erythrocytes, but its biological function is not yet known. Less specific cholinesterases are found in blood serum and certain organs and tissues of animals. The most active ACE has been discovered in the electric organs of fish of the suborder Batoidea. Individual cholinesterases of high purity have been obtained from various organs and tissues.

All cholinesterases are proteins with molecular weights ranging from 70,000 to 1,000,000; they contain no coenzymes of low molecular weight. A very important role in the catalytic activity of cholinesterases is played by the amino acids serine, histidine, aspartic acid, and glutamic acid.

V. A. IAKOVLEV

References in periodicals archive ?
Second, because of a lack of a baseline value, a reduction in cholinesterase from any value had to be considered a depression, without regard for time sequence.
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It should be noted, however, that RBC cholinesterase is more difficult to measure and is depressed more slowly than is plasma cholinesterase.
A rapid screening test for the determination of the approximate cholinesterase activity of human blood.
The degree of severity of AD is currently measured using the Mini-Mental State Evaluation (MMSE), a screening tool which clinicians state is not the best means for identifying who may benefit from cholinesterase inhibitors," explains Dr Ian Howe.
63-65) By inhibiting the degradation of acetylcholine released by presynaptic cholinergic neurons, cholinesterase inhibitors increase the amount of acetylcholine available for neurotransmission.
Cholinesterase inhibitors--These drugs block an enzyme that recycles acetylcholine, which appears to improve memory function in early-stage Alzheimer's patients when allowed to accumulate in the brain, or at least slow the disease's progression.
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Medications known as cholinesterase inhibitors provide a modest boost in memory for many Alzheimer's patients.
The colourless, odourless chemicals Tabun and Sarin kill by inhibiting the action of the body's enzyme cholinesterase, producing muscular paralysis on contact with the eyes or skin by as little as one milligram of the substance.