Copyright (c) by The American Society for Pharmacology and Experimental Therapeutics All rights of reproduction in any farm reserved. MOLECULAR PHARMACOLOGY, 37:950-957 Reconstitution of Muscarinic Receptor-Mediated Inhibition of

Inhibition of bovine brain calmodulin-sensitive adenylyl cyclase was examined in a system consisting of the reconstituted purified porcine atrial muscarinic acetylcholine receptor, the purified in-hibitory guanine nucleotide-binding protein (G), and the partially purified stimulatory guanine nucleotide-binding protein. adenylyl cyclase complex. Under conditions where G, existed mainly as the G. GOP complex, adenylyl cyclase was selectively preacti-vated with guanosine 5’-O-(3-thiotriphosphate) (GTP-yS). Addi-tion of carbachol formed the receptor. carbachol complex, which catalyzed the exchange of GOP bound to G, for GTP-YS, initiating G-mediated inhibition of adenylyl cyclase. Adenylyl cyclase acti-vated by calcium plus calmodulin was more sensitive to inhibition by carbachol than either unstimulated adenylyl cyclase or aden-ylyl cyclase activated by GTP’YS or forskolin. Studies using the resolved subunits of G, showed that the fy subunit could inhibi