Anticholinesterases / W.D.M. Paton.

  • William Paton
Date:
[1954?]
Catalogue details

Licence: In copyright

Credit: Anticholinesterases / W.D.M. Paton. Source: Wellcome Collection.

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    that they named it ‘true’ cholinesterase, while the second was only apparently concerned with this and hence was named ‘pseudo’-cholinesterase. They further showed that one could measure the true cholinesterase in a tissue or extract by the rate of hydrolysis of acetyl-p-methyl-choline (a substance chemically very like acetylcholine), and the pseudo-cholinesterase by the rate of hydrolysis of benzoylcholine (a rather different com¬ pound). This christening was soon challenged, partly because words like ‘true’ and ‘pseudo’ had an air of moral judgement, and partly because it was found that some cholinesterases existed whose properties diverged from those laid down. But these names reflect a useful physiological approach, and though they may be criticized, their use is convenient, nearly self- explanatory and not fundamentally misleading, since the con¬ ception implied has been generally accepted, even if the names have not. Other workers found that the ‘true’ cholinesterases could hydrolyse a number of substances possessing acetyl groups but not choline groups, so that they thought that a better name for the true enzyme would be ‘acetylase’. A third group of workers analysed the kinetics and specificity of the enzymes, stressing (1) the high rate of reaction of the true enzyme with acetyl¬ choline, (2) the fact that it seemed designed to work most efficiently in low dilution, and (3) the fact that it seemed to be fairly particular about the resemblance of its substrates to acetylcholine. They painted a picture whereby true cholinester¬ ase seemed to bear a highly specific relationship to acetylcholine while the pseudo-enzyme was not specifically concerned with it; hence the names ‘specific’ and ‘non-specific’ cholinesterase. A fourth approach arose from experiments varying the aliphatic chain in acetylcholine. This revealed that ‘true’ split acetyl esters more rapidly than any other ester, while the ‘pseudo’ split butyric esters much better. Hence the names ‘aceto-cholin- esterases’ and ‘butyro-cholinesterases’. A fifth approach is to abandon attempts to give an explanatory name and simply refer to them as ‘Group I’ and ‘Group II’ enzymes, or ‘a’ and ‘ p’ enzymes, names which could obviously be retained whatever properties were revealed about the enzymes. Another approach
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