Molecular Pharmacology, Vol 11, 722-734, Copyright © 1975 by the American Society for Pharmacology and Experimental Therapeutics

Effects of Edrophonium, Eserine, Decamethonium, d-Tubocurarine, and Gallamine on the Kinetics of Membrane-Bound and Solubilized Eel Acetylcholinesterase

¹ Departments of Pharmacology and Therapeutics and of Research in Anaesthesis, McGill Unversity, Montreal 109, Quebec, Canada

The effects of edrophonium, eserine, decamethonium, d-tubocurarine, and gallamine on the kinetic parameters of membrane-bound and solubilized eel acetylcholinesterase were investigated. All assays were done using acetylcholine as substrate with a pH-stat in Ringer's solution. Edrophonium, an inhibitor of the anionic portion of the active site of acetylcholinesterase, was found to be a competitive inhibitor at a concentration of 0.1 µM and a mixed competitive-noncompetitive inhibitor at higher concentrations (1 and 10 µM) for both membrane-bound and solubilized acetylcholinesterase. Eserine (0.2-20 µM), a molecule which interacts with both the anionic and the esteratic portion of the active site of acetylcholinesterase, was a competitive inhibitor of the solubilized enzyme; inhibition by eserine of the membrane-bound enzyme was noncompetitive at 0.2 µM and mixed competitive-noncompetitive at higher concentrations of eserine (2 and 20 µM). The inhibition by decamethonium of both membrane-bound and solubilized acetylcholinesterase was noncompetitive at 3 and 100 µM decamethonium. d-Tubocurarine was found to affect the kinetics of both states of the enzyme in a mixed competitive-noncompetitive fashion. Gallamine, at concentrations as high as 100 µM, had no significant effect on either the K_m or V_max of membrane-bound or solubilized acetylcholinesterase. The effects of the membrane matrix on the interaction of these drugs with eel acetylcholinesterase are discussed.

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ACKNOWLEDGMENTS We would like to thank Dr. J. Richardson and Ms. T. Bouchard for taking the electron micrographs, and Mr. H. P. Decker of Hoffmann-La Roche for a generous gift of edrophonium chloride.