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Journal Article

Proton Magnetic Resonance Studies of Cholinergic Ligand Binding to the Acetylcholine Receptor in its Membrane Environment

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Witzemann, Veit
Department of Molecular Neurobiology, Max Planck Institute for Medical Research, Max Planck Society;
Working Group Witzemann / Koenen, Max Planck Institute for Medical Research, Max Planck Society;
Molecular anatomy of the neuromuscular junction, Max Planck Institute for Medical Research, Max Planck Society;
Department of Cell Physiology, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Miller, J., Witzemann, V., Quast, U., & Raftery, M. A. (1979). Proton Magnetic Resonance Studies of Cholinergic Ligand Binding to the Acetylcholine Receptor in its Membrane Environment. Proceedings of the National Academy of Sciences of the USA (JSTOR), 76(8), 3580-3584. Retrieved from http://www.pnas.org/cgi/content/abstract/76/8/3580.

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 alpha −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 Delta H < 1.5 kcal/mol and allowed estimates for the dissociation rate constant of the receptor−choline complex (kdiss > 1.6 x 103 S1) and the respective activation energy, Ea (kdiss) approx 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