RECIPROCAL REGULATION OF G(S-ALPHA) BY PALMITATE AND THE BETA-GAMMA SUBUNIT

Hormonal activation of G(s), the stimulatory regulator of adenylyl cyc lase, promotes dissociation of alpha(s) from G beta gamma, accelerates removal of covalently attached palmitate from the G alpha subunit, an d triggers release of a fraction of alpha(s) from the plasma membrane into the cytosol. To elucidate relations among these three events, we assessed biochemical effects in vitro of attached palmitate on recombi nant alpha(s) prepared from Sf9 cells. In comparison to the unpalmitoy lated protein (obtained from cytosol of Sf9 cells, treated with a palm itoyl esterase, or expressed as a mutant protein lacking the site for palmitoylation), palmitoylated alpha(s) (from Sf9 membranes, 50% palmi toylated) was more hydrophobic, as indicated by partitioning into TX-1 14, and bound beta gamma with 5-fold higher affinity. beta gamma prote cted GDP-bound alpha(s), but not alpha(s) . GTP[gamma S], from depalmi toylation by a recombinant esterase. We conclude that beta gamma bindi ng and palmitoylation reciprocally potentiate each other in promoting membrane attachment of at, and that dissociation of alpha(s) . GTP fro m beta gamma is likely to mediate receptor-induced alpha(s) depalmitoy lation and translocation of the protein to cytosol in intact cells.