title: Interaction of the retinal G-protein transducin with uracil nucleotides.
abstract: Little is known about the interaction of pyrimidine nucleotides with G-proteins. Here we report that under experimental conditions that exclude transphosphorylation reactions, nucleoside 5'-triphosphates inhibited transducin-catalyzed GTP hydrolysis in the order of potency guanosine 5'-[gamma-thio]triphosphate > GTP > guanosine 5'-[beta,gamma-imido]triphosphate > uridine 5'-[gamma-thio]triphosphate > UTP > CTP. Nucleoside 5'-diphosphates inhibited GTP hydrolysis in the order of potency GDP approximately guanosine 5'-[beta-thio]thiodiphosphate > uridine 5'-[beta-thio]diphosphate >> UDP (no effect). UTP inhibited GTP hydrolysis competitively, indicative for nucleotide binding to the same site. Uracil nucleotides had a distinct activity profile with respect to disruption of the transitory complex between photoexcited rhodopsin and nucleotide-free transducin. We conclude that (i) uracil nucleotides bind to transducin-alpha with lower affinity than the corresponding guanine nucleotides, (ii) phosphorothioate modification of uracil nucleotides increases their affinity for transducin, and (iii) uracil nucleotides induce conformational changes in G-proteins that are different from the conformational changes induced by guanine nucleotides.
authors.affiliation: Institut für Pharmakologie, Freie Universität Berlin, Thielallee 69-73, Berlin, D-14195, Germany.
authors.forename: J F
authors.initials: JF
authors.lastname: Klinker
authors.forename: R
authors.initials: R
authors.lastname: Seifert
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D008027:Light; D012374:Rod Cell Outer Segment / Q000378:metabolism / Q000528:radiation effects; D015293:Transducin / Q000378:metabolism*; D014500:Uracil Nucleotides / Q000378:metabolism*; D014544:Uridine Triphosphate / Q000378:metabolism
chemical_list: D014500:Uracil Nucleotides; D006160:Guanosine Triphosphate; D015293:Transducin; D014544:Uridine Triphosphate