ADENYLYL-CYCLASE AND G-PROTEINS IN PHYTOMONAS

Phytomonas sp. membranes have an adenylyl cyclase activity which is gr eater in the presence of Mn2+ than with Mg2+. The Mg2+ and Mn2+ activi ty ratio varies from one membrane preparation to another, suggesting t hat the adenylyl cyclase has a variable activation state. A [S-35]GTP- gamma-S-binding activity with a Kd of 171 nM was detected in Phytomona s membranes. Incubation of these membranes with activated cholera or p ertussis toxin and [adenylate P-32]NAD(+) led to incorporation of radi oactivity into bands of about 40-44 kDa. Crude membranes were electrop horesed on SDS-polyacrylamide gels and analyzed, by Western blotting, with the 9188 anti-alpha, antibody and the AS/7 antibody (anti-alpha(1 ), anti-alpha(i1), anti-alpha(i2)). These procedures resulted in the i dentification of polypeptides of approximately 40-44 kDa. Phytomonas a denylyl cyclase could be activated by treatment of membrane preparatio ns with cholera toxin, in the presence of NAD(+), while similar treatm ent with pertussis toxin did not affect this enzyme activity. These st udies indicate that in Phytomonas, adenylyl cyclase activity is couple d to an unknown receptor entity through Gel, proteins.