Guanine nucleotide inhibition of adenylate cyclase in a membrane fraction from Dictyostelium discoideum.

The regulation of adenylate cyclase by guanine nucleotides was examined in a plasma membrane preparation from Dictyostelium discoideum. At concentrations of greater than 10 microM, GDP, GTP and a non-hydrolyzable GTP analogue, guanosine 5'-(beta-gamma-imino)triphosphate (Gpp(NH)p), inhibited the enzyme. Guanosine, GMP and ITP were ineffective. The inhibition was not affected by variations in assay conditions (membrane concentration, time or temperature), the presence of cAMP, NaF or forskolin in the reaction mix, or variations in the stage of Dictyostelium discoideum development. There was no stimulation of adenylate cyclase by GTP or Gpp(NH)p under any conditions. Inhibition of adenylate cyclase by Gpp(NH)p was sensitive to divalent cations. The addition of MnCl2 resulted in increased adenylate cyclase activity, but augmented the inhibitory response to Gpp(NH)p. The differences between Dictyostelium discoideum and eukaryotic regulation of adenylate cyclase by guanine nucleotides are discussed.