Adrenal cortex adenylate cyclase. Specific binding sites for 5'-guanylyl-imidodiphosphate in partially purified plasma membranes from bovine adrenal cortex

Abstract

Specific binding sites for 5'-guanylyl-imidodiphosphate [Gpp(NG)p] have been identified in a partially purified plasma membrane fraction from bovine adrenal cortex. The apparent affinity of Gpp(nh)p at 30 degrees C was 12muM-1 and the concentration of binding sites was 100 pmoles per mg of protein. Binding of Gpp(NH)p is inhibited by Mn2+ greater than Mg2+ greater than Ca2+ and enhanced by low concentrations of the chelators ethylenediamino-tetraacetic acid (EDTA) and ethylene glycolbis-(beta-aminoethylether))-N,N'-tetraacetic acid (EGTA). High concentrations of EDTA are inhibitory and at 2.5 mM EDTA binding of Gpp(NH)p is only 10% of that observed in the absence of the chelator. The bound labeled GTP analogue exchanged only slowly with the unlabeled nucleotide after a steady state has been reached. EDTA also releases the bound labeled Gpp(NH)p from its binding sites. The slow dissociation of Gpp(NH)p can explain the persistent activation of adenylate cyclase observed after pretreatment of bovine adrenal cortex plasma membranes with Gpp(NH)p and subsequent washing. It is suggested that at least parts of these binding sites are identical to the sites identified earlier as regulatory sites for angiotensin high-affinity receptors (Glossmann et. al., 1974a) and for ACTH-stimulated cyclase Glossmann and Gips, 1974).