title: Stimulation and inhibition of human platelet adenylylcyclase by thiophosphorylated transducin beta gamma-subunits.
abstract: The effect of beta gamma-dimers isolated from the retinal guanine nucleotide-binding protein (G protein) transducin eluted from illuminated bovine rod outer segment membranes with GTP, guanosine 5'-O-(beta, gamma-imino)triphosphate (Gpp(NH)p), or guanosine 5'-O-(gamma-thio)triphosphate (GTP gamma S) on basal and forskolin-stimulated adenylylcyclase activities in membranes of human platelets was studied. beta gamma-Subunits isolated from transducin eluted with GTP gamma S (TD beta gamma GTP gamma S) had a concentration-dependent stimulatory effect on basal adenylylcyclase activity. The stimulatory agonist prostaglandin E1 increased the potency and the maximum extent of stimulation due to TD beta gamma GTP gamma S). With a similar concentration dependence, TD beta gamma GTP gamma S exerted an inhibitory influence on forskolin-stimulated adenylylcyclase activity. At the same concentrations, beta gamma-dimers isolated with either GTP or Gpp(NH)p did not alter enzyme activities. The observed effects of TD beta gamma GTP gamma S were similar to those of directly added GTP gamma S with regard to maximum levels, time dependence, and persistence; however, TD beta gamma GTP gamma S was approximately 10-fold more potent than GTP gamma S. Treatment of TD beta gamma GTP gamma S, but not of free GTP gamma S, with hydroxylamine caused a loss of adenylylcyclase regulation by TD beta gamma GTP gamma S. The data presented indicated that TD beta gamma GTP gamma S potently and efficiently activates the stimulatory and inhibitory G proteins of adenylylcyclase in human platelet membranes. Furthermore, evidence is provided suggesting that the observed effects of TD beta gamma GTP gamma S, which can be thiophosphorylated by GTP gamma S at the beta-subunit (Wieland, T., Ulibarri, I., Gierschik, P., and Jakobs, K. H. (1991) Eur. J. Biochem. 196, 707-716), are due to formation of GTP gamma S at the G proteins.
authors.affiliation: Institut für Pharmakologie, Universität GH Essen, Federal Republic of Germany.
authors.forename: T
authors.initials: T
authors.lastname: Wieland
authors.forename: M
authors.initials: M
authors.lastname: Ronzani
authors.forename: K H
authors.initials: KH
authors.lastname: Jakobs
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000097:blood*; D000527:Alprostadil / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D002417:Cattle; D005576:Colforsin / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D013873:Thionucleotides / Q000494:pharmacology*; D015293:Transducin / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D046911:Macromolecular Substances; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D006160:Guanosine Triphosphate; D015293:Transducin; D000262:Adenylyl Cyclases; D000527:Alprostadil