Molecular Pharmacology, Vol 14, 531-539, Copyright © 1978 by the American Society for Pharmacology and Experimental Therapeutics

Efficiency of Coupling between the Beta Adrenergic Receptor and Adenylate Cyclase

¹ Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22903

Under experimental conditions in which the coupling between the beta adrenergic receptor and adenylate cyclase was altered in S49 lymphoma cell membranes, changes were observed in the ratio of K_D to K_act for beta adrenergic agonists and in the effects of guanine nucleotide on the binding of agonists. The K_D for isoproterenol binding to the beta adrenergic receptor was greater than the K_act for enzyme activation, despite the use of a simultaneous assay technique. The ratio of K_D to K_act was decreased under conditions of less efficient coupling, such as in the presence of filipin or stimulation by partial agonists. However, cholera toxin treatment, which improves coupling efficiency, increased the ratio of K_D to K_act for both full and partial agonists. The ability of guanine nucleotides to decrease the affinity of the beta adrenergic receptor for agonists was lost when membranes were treated with filipin or 10 mM N-ethylmaleimide. However, 1 mM N-ethylmaleimide, a concentration sufficient to inhibit over 90% of adenylate cyclase activity in this membrane preparation, was ineffective in altering the binding characteristics. The effect of guanine nucleotide can thus be observed in the absence of a functional catalytic unit of adenylate cyclase.