Molecular Pharmacology, Vol 4, 181-186, Copyright © 1968 by the American Society for Pharmacology and Experimental Therapeutics

The Acceleration of Acetylcholinesterase Activity at Low Ionic Strength by Organic and Inorganic Cations

¹ Department of Pharmacy, University of Sydney, Sydney, N.S.W., Australia

The effect of three tetraalkylammonium compounds on the hydrolysis of phenylacetate by acetylcholinesterase at low ionic strength has been examined. Tetraethylammonium iodide is shown to increase noncompetitively the maximum velocity of hydrolysis, probably by accelerating the rate-limiting deacetylation step of the hydrolysis. Tetramethylammonium iodide acts as a purely competitive inhibitor, while tetra-n-propylammonium iodide decreases the maximum velocity, probably by blocking deacetylation. The effects of MgCl₂ and NaCl on phenylacetate hydrolysis have been studied, and a competition between organic and inorganic cations for the anionic site of acetylated acetylcholinesterase proposed.

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ACKNOWLEDGMENTS This investigation was supported in part by grants from the National Health and Medical Research Council of Australia and a research scholarship (B.D.R.) from the Pharmaceutical Society of New South Wales S. E. Wright Research Trust. The authors wish to thank Mr. J. Robinson for discussions on the statistical analysis of results and Miss Pamela Poole for executing a computer program for their analysis.