Molecular Pharmacology, Vol 8, 575-581, Copyright © 1972 by the American Society for Pharmacology and Experimental Therapeutics

Acetylcholinesterase

I. A Study by Nuclear Magnetic Resonance of the Binding of Inhibitors to the Enzyme

¹ Department of Research in Anaesthesia and the Department of Pharmacology and Therapeutics, McGill University, Montreal 101, Quebec, Canada

A nuclear magnetic resonance method has been used to study the binding of atropine and eserine to purified squid acetylcholinesterase (EC 3.1.1.7). The dissociation constant, K_D, and the linewidth of the acetylcholinesterase-inhibitor complex, _bound, for atropine and eserine were estimated from the linewidth changes of the N-methyl and phenyl group resonances of atropine and from the N-methyl and C-methyl group resonances of eserine resulting from association with the enzyme. The results indicate that there is at least one binding site on the enzyme surface for atropine and one for eserine. Further evidence that the two sites are distinct is demonstrated by the fact that gallamine displaces atropine from its site without competing with eserine.