Abstract
Interaction of cholinergic effectors with eel acetylcholinesterase was investigated in physiological eel Ringer's solution, pH 7. The acceleration of methanesulfonation of the soluble enzyme by the cholinergic agonists decamethonium and trimethylbutylammonium ions was indistinguishable from that observed with the membrane-bound enzyme. Maximum acceleration of the methanesulfonation reaction by decamethonium and succinylcholine with the particulate acetylcholinesterase was essentially the same. A limited acceleration caused by trimethylbutylammonium ion is attributed to its partial overlap with the esteratic site, in contrast to the postulated "exo" mode of binding for the bisquaternary accelerator, decamethonium. Kinetic studies with trimethylbutylammonium and decamethonium ions using acetylcholine and phenyl acetate as substrates, as well as equilibrium binding studies to the enzyme, support the "exo" mode of binding for decamethonium, the "endo" mode of binding for 3-hydroxyphenyltrimethylammonium ion, and an intermediate mode of binding for trimethylbutylammonium ion. The effects produced by the quaternary nitrogen agonists on acetylcholinesterase in physiological eel Ringer's solution can be explained on the basis of binding of the effectors to the anionic subsite of the active center.
ACKNOWLEDGMENTS The author thanks Dr. G. P. Hess for the use of facilities, and Dr. Juain Fu for providing the least-squares program.
- Copyright ©, 1973, by Academic Press, Inc.
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