title: Agonist-stimulated high-affinity GTPase in Dictyostelium membranes.
abstract: GTP hydrolysis in Dictyostelium discoideum membranes is caused by a low (Km greater than 1 mM) and a high affinity (Km 6.5 microM) GTPase. cAMP enhances GTP hydrolysis apparently by increasing the affinity of the high affinity GTPase (stimulated Km 4.5 microM); the low affinity GTPase was not affected by cAMP. Stimulation of GTP hydrolysis by cAMP was maximal at early time points and declined thereafter. A half-maximal stimulation of GTPase occurred at 3 microM cAMP and the specificity of cAMP derivatives for stimulation of GTPase activity showed a close correlation with the specificity for binding to the cell surface cAMP receptor. Treatment of D. discoideum cells with pertussis toxin decreased the cAMP-induced stimulation of GTPase from 42 +/- 6% in control cells to 17 +/- 9% in pertussis toxin-treated cells. These results suggest that the interaction of cAMP with its surface receptor leads to stimulation of high affinity GTPase in D. discoideum membranes. At least one of those enzymes may represent a guanine nucleotide-binding protein sensitive to pertussis toxin.
authors.affiliation: Cell Biology and Genetics Unit, Zoological Laboratory, Leiden, The Netherlands.
authors.forename: B E
authors.initials: BE
authors.lastname: Snaar-Jagalska
authors.forename: K H
authors.initials: KH
authors.lastname: Jakobs
authors.forename: P J
authors.initials: PJ
authors.lastname: Van Haastert
mesh_terms: D002462:Cell Membrane / Q000201:enzymology; D000242:Cyclic AMP / Q000378:metabolism*; D004023:Dictyostelium / Q000201:enzymology*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D037342:Pertussis Toxin; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011953:Receptors, Cyclic AMP / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D011953:Receptors, Cyclic AMP; D010566:Virulence Factors, Bordetella; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D037342:Pertussis Toxin; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases