title: Role of guanine nucleotides in the stimulation of thyroid adenylate cyclase by prostaglandin E1 and cholera toxin.
abstract: Cholera toxin in the presence of GTP increased adenylate cyclase activity in a purified bovine thyroid plasma membrane preparation, whereas, in the presence of guanosine 5'-(beta, gamma-imido)-triphosphate (Gpp(NH)P), cholera toxin had no stimulatory effect. Similarly, prostaglandin E1 enhanced the adenylate cyclase activity induced by GTP but not by Gpp(NH)p. Gpp(NH)p-stimulated adenylate cyclase activity, assayed with hydrolysis-resistant adenosine 5'-(beta, gamma-imido)-[32P]triphosphate as substrate and no ATP-regenerating system was inhibited by GDP in a competitive fashion. Furthermore, prostaglandin E1, but not cholera toxin, influenced the GDP inhibition of Gpp(NH)p-stimulated activity by increasing the concentration of GDP resulting in 50% inhibition approx. 2-fold. Inosyl nucleotides mimicked the effects of guanyl nucleotides on thyroid adenylate cyclase in that ITP could substitute for GTP in enhancing cholera toxin- and prostaglandin #1-induced activities and that inosine 5'(beta, gamma-imido)-triphosphate [Ipp(NH)p] was also a potent stimulator per se. Conclusions. (1) Cholera Toxin and prostaglandin E1 enhance thyroid adenylate cyclase activation by GTP (or ITP), but have no stimulatory effect on the Gpp(NH)p (or Ipp(NH)p) response; (2) the stimulatory effect of prostaglandin E1 on adenylate cyclase may result from decreased affinity for GDP at the guanine nucleotide regulatory site; (3) the date regarding cholera toxin stimulation of thyroid adenylate cyclase are consistent with the hypothesis that cholera toxin exerts its effect by inhibiting an endogenous GTPase.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002772:Cholera Toxin / Q000494:pharmacology*; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007290:Inosine Diphosphate / Q000494:pharmacology; D007293:Inosine Triphosphate / Q000494:pharmacology; D011458:Prostaglandins E / Q000494:pharmacology*; D013961:Thyroid Gland / Q000187:drug effects / Q000201:enzymology*
chemical_list: D006150:Guanine Nucleotides; D011458:Prostaglandins E; D007293:Inosine Triphosphate; D006153:Guanosine Diphosphate; D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate; D007290:Inosine Diphosphate; D002772:Cholera Toxin; D000262:Adenylyl Cyclases