ACTIVATED G(S-ALPHA) BUT NOT G(I-ALPHA) PREVENTS THE THERMAL INACTIVATION OF ADENYLYL-CYCLASE IN PLASMA-MEMBRANES DERIVED FROM S49 LYMPHOMA-CELLS

The thermal inactivation of adenylyl cyclase was studied in plasma mem branes isolated from wild-type and the mutant cell strain cyc(-) of S4 9 lymphoma. The half-life of adenylyl cyclase activity at 30 degrees C was decreased from 14.2 min to 3.4 min by the presence of detergents. ATP as well as forskolin prevented the adenylyl cyclase inactivation in a dose-response manner independent of the utilized type of cell mem branes. Activation of G-proteins by GTP gamma S or by AlF4- in wild-ty pe membranes but not in cyc(-) membranes partially prevented adenylyl cyclase inactivation. Adenylyl cyclase activity in cyc(-) membranes wa s preserved in the presence of GTP gamma S or AlF4- from the observed detergent-induced inactivation by complementation of these membranes w ith an extract from wild-type membranes. ADP-ribosylation of G(i alpha ) in cyc(-) membranes did not influence the kinetics of the inactivati on process of adenylyl cyclase, whereas ADP-ribosylated G(s alpha) pro tein protected adenylyl cyclase more effectively than non-ribosylated G(s alpha) in wild-type plasma membranes when GTP was used as an activ ator.