REGULATION OF CYCLIC NUCLEOTIDE METABOLISM

1)对腺苷酸敏感的腺苷酸环化酶的调节是 由两个鸟嘌呤核苷酸结合（G）蛋白介导， 通过Gs刺激，通过Gi抑制。 在视觉 兴奋系统，一个类似的G蛋白，Gt或转导蛋白， 光子受体视紫红质转化为环GMP磷酸二酯酶。 这些G蛋白是α、β和γ的异源三聚体 亚单位。 α亚单位结合鸟嘌呤核苷酸， 水解GTP。 β γ亚基促进 α到受体。 为了确定G γ的函数， 制备小鼠抗Gt γ单克隆抗体（2 H3）。 2 H3对Gt γ具有特异性，不识别G γ 肝脏或大脑 2 H3与Gt α β γ的相互作用 似乎有助于G蛋白解离成其 百日咳监测的α和β-γ成分 毒素催化的ADP-核糖基化（有利于异源三聚体 并被2 H3抑制）和免疫沉淀（其中β γ被沉淀，但α未被沉淀）。 存在下 受体，2 H3的作用减弱，与 假设Gt γ上的结构域在视紫红质中被掩蔽 Gt复合体。 因此，这些研究支持了G γ在一个 蛋白质-受体偶联 2)细菌毒素，如百日咳 和霍乱毒素，通过ADP发挥它们对细胞的作用- G蛋白的核糖基化;这种修饰导致改变 功能 在霍乱毒素的情况下，Gs α导致腺苷酸环化酶活化。 一种新的毒素， 大肠杆菌（LT-II）对ADP-核糖基化反应具有催化作用 的Gs α，导致腺苷酸环化酶的激活，这表明 LT-II和霍乱毒素，两种非同源的， 免疫学上不同的毒素，共享一个共同的机制， 行动上

1) Regulation of the hormone-sensitive adenylate cyclase is mediated by two guanine nucleotide-binding (G) proteins, stimulation through Gs, inhibition through Gi. In the visual excitation system, a similar G protein, Gt or transducin, couples the photon receptor rhodopsin to a cyclic GMP phosphodiesterase. These G proteins are heterotrimers of alpha, beta, and gamma subunits. The alpha subunits bind guanine nucleotide and hydrolyze GTP. The beta gamma subunits facilitate coupling of alpha to receptor. To determine the function of G gamma, a mouse anti-Gt gamma monoclonal antibody (2H3) was prepared. 2H3 was specific for Gt gamma and did not recognize G gamma from liver or brain. Interaction of 2H3 with Gt alpha beta gamma appeared to facilitate the dissociation of the G protein into its alpha and Beta gamma components, as monitored by pertussis toxin-catalyzed ADP-ribosylation (which favors the heterotrimer and is inhibited by 2H3) and immunoprecipitation (in which Beta gamma was precipitated but not alpha). In the presence of receptor, the effect of 2H3 was diminished, consistent with the hypothesis that a domain on Gt gamma is masked in the rhodopsin Gt complex. The studies, thus, support a role of G gamma in a protein-receptor coupling. 2) Bacterial toxins, such as pertussis and cholera toxins, exert their effects of cells through the ADP- ribosylation of G proteins; this modification leads to altered function. In the case of cholera toxin, ADP-ribosylation of Gs alpha results in adenylate cyclase activation. A novel toxin from Escherichia coli (LT-II) appeared to catalyze the ADP-ribosylation of Gs alpha, leading to activation of adenylate cyclase, suggesting that LT-II and cholera toxin, two nonhomologous and immunologically different toxins, share a common mechanism of action.