The guanine nucleotide-binding regulatory component of adenylate cyclase in human erythrocytes

The guanine nucleotide-binding regulatory component of adenylate cyclase (G/F) has been purified from human erythrocyte membranes. It is composed of two major polypeptides with molecular weights of 35,000 and 45,000. When cyc^- S49 lymphoma cell plasma membranes are reconstituted with purified human erythrocyte G/F, stimulation of adenylate cyclase by β-adrenergic agonists, guanine nucleotides, and fluoride is restored. Binding of GTPγS to human erythrocyte G/F and GTPγS-mediated activation of the protein are closely correlated. The agreement between the apparent dissocation constants for these two reactions suggests that the measured binding site is identical to the site responsible for activation. A 41,000-dalton protein has been identified as a contaminant of preparations of G/F that have been purfied by four succesive chromatographic steps. This protein serves as a specific substrate for ADP-ribosylation and labeling by islet activating protein (IAP) and [³²P]NAD, and it appears to contribute an additional high-affinity guanine nucleotide binding site to such preparations.