REGULATION OF CYCLIC NUCLEOTIDE METABOLISM

1)激素敏感的腺苷环化酶的调节是 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。在视觉上 激发系统，类似的G蛋白，GT或转导蛋白，对 光感受器视紫红质转化为环状GMP磷酸二酯酶。 这些G蛋白是α、β和伽马的异源三聚体 亚单位。α亚基与鸟嘌呤核苷酸结合， GTP的水解液。β-伽马亚基促进了 阿尔法呼叫接收器。为了确定G伽马的函数，a 制备了小鼠抗GT-γ单抗(2H3)。 2H3专用于GT伽马，不识别G伽马 来自肝脏或大脑。2H3与GTαβ伽马的相互作用 似乎促进了G蛋白解离成其 百日咳监测的Alpha和Beta伽马成分 毒素催化的ADP-核糖基化(有利于杂三聚体 并被2H3)和免疫沉淀(其中Beta 伽马是沉淀的，但不是阿尔法)。在……面前 受体后，2H3的作用减弱，与 假设GT上的结构域在视紫红质中被掩盖 GT复合体。因此，这些研究支持了G伽马在 蛋白质-受体偶联。2)细菌毒素，如百日咳 和霍乱毒素，通过ADP发挥其对细胞的作用- G蛋白的核糖化；这种修饰导致改变 功能。在霍乱毒素的情况下，Gs的ADP核糖基化 阿尔法导致腺苷环化酶激活。一种新的来自中国的毒素 大肠杆菌(LT-II)似乎催化ADP-核糖化 Gsα，导致腺苷酸环化酶激活，提示 LT-II和霍乱毒素，两个不同源的和 免疫学上不同的毒素，有着共同的机制 行动。

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.