The absolute activity of choline-esterase

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Abstract
The rate at which choline esterase hydrolysed choline esters decreased in the series n-butyryl > propionyl > iso-butyl > acetyl > benzoyl, the rate increasing in n-acids with the size of the acyl group, unless a sidechain was introduced. The rate of non-enzymatic hydrolysis was proportional to the cH, and decreased with increase in size of the aliphatic acyl group, so that the above series was practically reversed. In both series, the rate was influenced by pH. Inhibition of the esterase by physostigmine and allied drugs was reversible. The inhibitory action of miotine was the same with different substrates. Miotine was unstable in aqueous solution, prostigmine was stable, but both were slowly decomposed by the enzyme. Assuming that the inhibition is produced by the combination of one molecule of the inhibitor with one active center of the enzyme, and follows the law of mass action, and that combination of the enzyme with its substrate occurs in the same manner, the rate of hydrolysis of the substrate could be calculated from the inhibition produced by a known concentration of inhibitor. At room temp., at a pH of 7.4, one active center of choline-esterase was calculated to hydrolyse 3850 molecules of butyryl choline, or 1490 molecules of acetyl choline, per second. Details of the preparation of the esters are given in an appendix.