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Molecular Pharmacology, Vol 8, 41-49, Copyright © 1972 by the American Society for Pharmacology and Experimental Therapeutics

Relative Binding Sites of Pharmacologically Active Ligands on Bovine Erythrocyte Acetylcholinesterase

B. D. ROUFOGALIS 1 and E. E. QUIST 1

1 Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver 8, British Columbia, Canada

The kinetics of the interaction of partially purified bovine erythrocyte acetylcholinesterase (EC 3.1.1.7) with calcium, tetramethylammonium, tetraethylammonium, decamethonium, gallamine, and d-tubocurarine has been investigated, using acetylcholine as substrate. Antagonism between various combinations of ligands has been studied. Decamethonium binds to the catalytic anionic site (agr) and to an allosteric site (beta). Calcium (0.2 mM) competes with decamethonium but not with acetylcholine, and is considered to act at the beta-anionic site. This is an accelerator site, which may bind tetraethylammonium and possibly other polar cations. Tetraethylammonium may also bind to the catalytic site, agr. Tetramethylammonium, which is not an accelerator, is considered to bind to the catalytic site exclusively. Neither tetramethylammonium, tetraethylammonium, nor calcium antagonizes the binding of gallamine. This observation, together with that of the partially competitive nature of the inhibition by gallamine, indicates that gallamine cannot bind to the agr- or beta-anionic sites and hence must bind to a second allosteric site, ggr. The ability of gallamine to antagonize inhibition by decamethonium is attributed to allosteric perturbations of the agr- and beta-sites induced by the action of gallamine at the ggr-site.

Note:
ACKNOWLEDGMENT Excellent technical assistance in the latter stages of this work was provided by Mrs. Virginia Wickson.

Submitted on August 9, 1971




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