Proton magnetic resonance studies of cholinergic ligand binding to the acetylcholine receptor in its membrane environment
Abstract
Proton magnetic resonance has been used to monitor binding of choline, a known partial agonist, to acetylcholine receptor-enriched membrane preparations from Torpedo californica electroplax. The interaction between choline and receptor led to a broadening of the resonance of the choline methyl groups and this effect was reversed by α-bungarotoxin, a quasi-irreversible antagonist of the acetylcholine receptor. From the concentration dependence of line broadening the equilibrium dissociation constant for choline was obtained (Kd = 190 ± 65 µ M). The temperature dependence of the parameters observed in the choline titrations gave an enthalpy of binding ΔH < 1.5 kcal/mol and allowed estimates for the dissociation rate constant of the receptor-choline complex (kdiss > 1.6 x 10^3 S1) and the respective activation energy, Ea (kdiss) ≈ 5.5 kcal/mol. The association of other ligands with the membrane-bound receptor could also be studied by observing effects of varying concentrations of such ligands on the choline methyl group linewidth at a constant choline concentration.
Additional Information
© 1979 by the National Academy of Sciences. Communicated by John D. Roberts, May 10, 1979. The authors thank Profs. F. W. Dahlquist, John Richards, and Michael Schimerlik for valuable comments and criticism. We are especially grateful to Professor Dahlquist and the Chemistry Department, University of Oregon, for allowing us use of the instrumentation on which these experiments were performed. We also thank John Racs for preparing the membrane fragments and Valerie Purvis and Carolyn Sprague for typing the manuscript. This research was supported by U.S. Public Health Service Grant NS-10294, by a grant from the Muscular Dystrophy Association of America, by a grant from the American Heart Association (Los Angeles, Affiliate), and by fellowships (to V.W. and U.Q.) from the Deutscheforschungsgemeinschaft. This is contribution no. 5951 of the Division of Chemistry and Chemical Engineering, California Institute of Technology. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.Files
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- Eprint ID
- 9007
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- CaltechAUTHORS:MILpnas79
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2007-10-20Created from EPrint's datestamp field
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