GUANINE-NUCLEOTIDE INHIBITION OF ADENYLATE-CYCLASE IN A MEMBRANE-FRACTION FROM DICTYOSTELIUM-DISCOIDEUM

Abstract

The regulation of adenylate cyclase by guanine nucleotides was examined in a plasma membrane preparation from Dictyostelium discoideum. At concentrations of greater than 10 .mu.M, GDP, GTP and a non-hydrolyzable GTP analog, 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 D. discoideum development. There was no stimulation of adenylate cyclase by 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 D. discoideum and eukaryotic regulation of adenylate cyclase by guanine nucleotides are discussed.