Activation of the inhibitory GTP-binding protein of adenylate cyclase, Gi, by beta-adrenergic receptors in reconstituted phospholipid vesicles.

beta-Adrenergic receptors and the inhibitory GTP-binding protein, Gi of the adenylate cyclase system were reconstituted into phospholipid vesicles by the method described previously for reconstituting receptors and the stimulatory GTP-binding protein, Gs (Brandt, D. R., Asano, T., Pedersen, S. E., and Ross, E. M. (1983) Biochemistry 22, 4357-4362). In the receptor-Gi vesicles, beta-adrenergic agonists stimulated both the high-affinity binding of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) to Gi and GTPase activity to an extent similar to that observed in vesicles containing beta-adrenergic receptors and Gs. Stimulation required receptors and displayed appropriate beta-adrenergic specificity. The prior treatment of receptor-Gi vesicles with islet-activating protein (pertussis toxin) plus NAD markedly inhibited both the isoproterenol-stimulated binding of GTP gamma S and the isoproterenol-stimulated GTPase activity. No contamination of Gi by Gs was apparent. These data suggest that receptors that typically stimulate adenylate cyclase activity may also activate the inhibitory system, perhaps as one mechanism of desensitization.