Antibodies generated to a synthetic decapeptide, RMHLRQYELL, representing the carboxyl-terminus of Gs-ct have been characterized in immunoblots and functional studies. This antibody, designated RM, reacts exclusively with a doublet of proteins of 52 and 45 kDa in immunoblots of bovine brain and wild-type $49 murine lymphoma cell membranes. No such reactivity is seen in membranes from cyc-$49 cells, which lack Gs. RM blocks receptor-mediated activation of Gs and adenylyl cyclase in membranes from wild-type $49 cells. RM could also immunoprecipitate adenylyl cyclase activity in detergent extracts from GTP[),]S-or fluoride-preactivated bovine brain membranes; thus binding of cts to effector and carboxyl-terminal antibody was mutually compatible. Such experiments provide an approach for the elucidation of functionally relevant interactions of G-proteins with receptors and effectors in the membrane.

Receptors for calcitonin, determined by activation of adenylate cyclase, were found in a distribution among zones of the kidney distinct from that of receptors for parathyroid hormone or vasopressin. Competitive binding studies showed that the receptors for calcitonin are similar in kidney and bone and that their high apparent affinity for salmon calcitonin accounts in part for the high biological potency in vivo of salmon calcitonin.

An iodine-labeled beta-adrenergic inhibitor ((125)l-hydroxybenzylpindolol) binds specifically to a site on turkey erythrocyte membranes. A series of beta-adrenergic agonists and inhibitors compete for this binding site, with apparent affinities paralleling biological effectiveness as activators or inhibitors of catecholaminestimulated adenylate cyclase. The activity of d-(+) agonists or inhibitors was 1 percent (or less) than that of the corresponding l-(-) isomers in competing for binding of the iodinated blocker as well as in affecting catecholamine-stimulated adenylate cyclase. 1-(-)-Norepinephrine was about one-tenth as active as l-(-)-isoproterenol in competing for the beta-blocking agent site. The stereospecificity of the interaction with the iodinated beta-blocking agent and the correspondence between affinity for site and biological potency of analogs suggested that this interaction is involved in function of the beta-adrenergic receptor.