of pertussis toxin-catalyzed ADP-ribosylation on interactions of transducin and the inhibitory GTP-binding protein of adenylate cyclase with guanyl nucleotides.

Release of bound [3H]Gpp(NH)p from NG108-15 cell membranes was induced by carbamylcholine, enkephalinamide, and norepinephrine, all of which inhibit adenylate cyclase. Release was blocked by antagonist, was greater with multiple agonists than with one, and required guanyl nucleotides. With membranes from pertussis toxin-treated cells, both total [3H] Gpp(NH)p binding and agonist-induced [3H]Gpp(NH)p release was decreased. ADP-ribosylation by toxin of transducin, the retinal GTP-binding protein which is similar in structure and function to that in cyclase, decreased [3H]Gpp(NH)p binding. Thus, the inability to demonstrate agonist-induced [3H]Gpp(NH)p release from toxin-treated NG108-15 membranes may result in part from absence of bound [3H]Gpp(NH)p.