Friedman Y, Lang M, Burke G
Biochim Biophys Acta. 1981 Feb 18;673(1):114-23.
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.
在存在GTP的情况下，霍乱毒素可增加纯化的牛甲状腺质膜制剂中的腺苷酸环化酶活性，而在存在鸟苷5'-（β，γ-亚氨基）-三磷酸（Gpp(NH)P）的情况下，霍乱毒素没有刺激作用。同样，前列腺素E1增强了由GTP而非Gpp(NH)p诱导的腺苷酸环化酶活性。以抗水解的腺苷5'-（β，γ-亚氨基）-[32P]三磷酸为底物且无ATP再生系统时，Gpp(NH)p刺激的腺苷酸环化酶活性受到GDP的竞争性抑制。此外，前列腺素E1而非霍乱毒素通过增加GDP浓度影响了GDP对Gpp(NH)p刺激活性的抑制作用，导致50%抑制的浓度约增加2倍。肌苷核苷酸模拟了鸟苷核苷酸对甲状腺腺苷酸环化酶的作用，因为ITP可替代GTP增强霍乱毒素和前列腺素#1诱导的活性，且肌苷5'（β，γ-亚氨基）-三磷酸[Ipp(NH)p]本身也是一种有效的刺激剂。结论：（1）霍乱毒素和前列腺素E1通过GTP（或ITP）增强甲状腺腺苷酸环化酶的激活，但对Gpp(NH)p（或Ipp(NH)p）反应无刺激作用；（2）前列腺素E1对腺苷酸环化酶的刺激作用可能源于鸟嘌呤核苷酸调节位点对GDP的亲和力降低；（3）关于霍乱毒素刺激甲状腺腺苷酸环化酶的数据与霍乱毒素通过抑制内源性GTP酶发挥作用的假说一致。
