DISTINCT PATTERNS OF BIDIRECTIONAL REGULATION OF MAMMALIAN ADENYLYL CYCLASES

The capacities of the cu subunits of pertussis toxin-sensitive guanine nucleotide-binding regulatory proteins (G proteins) to inhibit differ ent isoforms of mammalian adenylyl cyclases were assessed. Membranes f rom Sf9 cells infected with recombinant baculoviruses encoding either type I, II, V, or VI adenylyI cyclase were reconstituted with purified G protein subunits. Types V and VI adenylyl cyclase are most sensitiv e to inhibition by G(i alpha 1) G(i alpha 2) and G(i alpha 3); type I adenylyl cyclase can be inhibited by these three G(i alpha) proteins a nd by G(o alpha) as well. Type II adenylyl cyclase appears to be immun e to inhibition by these proteins. Examination of the effects of nativ e and mutant G(i alpha) proteins, as well as analysis of competition f or binding of G(s alpha) to adenylyl cyclases, indicate that at least certain adenylyl cyclases have independent sites for interaction with G(s alpha) (site 1, stimulatory) and G(i alpha) (site 2, inhibitory). High concentrations of G(i alpha) can interact with site 1 on types I and II adenylyl cyclase and activate the enzymes. Types I and II adeny lyl cyclase also appear to have independent sites for interaction with G protein beta gamma subunits. The type I enzyme is strongly inhibite d, while type II adenyIyI cyclase is activated if G(s alpha) is also p resent.