ACTIVATION OF DICTYOSTELIUM-DISCOIDEUM GUANYLATE-CYCLASE BY ATP

ATP activates guanylate cyclase in cells of Dictyostelium discoideum. The K0.5 for ATP activation is about 50 μM and saturates at about 0.3 mM ATP. Guanylate cyclase activity in crude extracts of D. discoideum shows Michaelian kinetics with a Km of about 1.0 mM GTP and Vmax of about 30 pmoles cyclic GMP/min/106 cells. In the presence of 0.3 mM ATP the enzyme kinetics is also Michaelian, the Km is lowered to about 0.2 mM GTP and the Vmax remains unchanged. Neither adenylyl-imidodiphosphate nor adenylyl (β,γ-methylene) diphosphonate can substitute ATP as activator of guanylate cyclase. The polyene antibiotic filipin inhibits basal guanylate cyclase activity while ATP activation is not affected. © 1979.