Evidence for a rabbit luteal ADP-ribosyltransferase activity which appears to be capable of activating adenylyl cyclase.

1. An ADP-ribosyltransferase activity which appears to be capable of activating adenylyl cyclase was identified in a plasma membrane fraction from rabbit corpora lutea and partially characterized by comparing the properties of the luteal transferase with those of cholera toxin. 2. Incubation of luteal membranes in the presence of GTP and varying concentrations of NAD resulted in concentration-dependent increases in adenylyl cyclase activity. 3. Stimulation of adenylyl cyclase by NAD and cholera toxin plus NAD was observed in the presence of GTP but not in the presence of guanosine-5'-O-(2-thiodiphosphate) or guanyl-5'-yl imidodiphosphate. 4. NAD or cholera toxin plus NAD reduced the Kact values for luteinizing hormone to activate adenylyl cyclase 3- to 3.5-fold. 5. NAD or cholera toxin plus NAD increased the extent to which cholate extracts from luteal membranes were able to reconstitute adenylyl cyclase activity in S49 cyc- mouse lymphoma membranes. 6. It was necessary to add ADP-ribose and arginine to the incubation mixture in order to demonstrate cholera toxin-specific ADP-ribosylation of a protein corresponding to the alpha subunit of the stimulatory guanine nucleotide-binding regulatory component (alpha Gs). 7. Treatment of luteal membranes with NAD prior to incubation in the presence of 32P]NAD plus cholera toxin resulted in reduced labeling of alpha Gs. 8. Endogenous ADP-ribosylation of alpha Gs was enhanced by Mg but was not altered by guanine nucleotide, NaF or luteinizing hormone and was inhibited by cAMP. 9. Incubation of luteal membranes in the presence of 32P]ADP-ribose in the absence and presence of cholera toxin did not result in the labeling of any membrane proteins.