Kimura N, Shimada N
Biochem Biophys Res Commun. 1986 Jan 29;134(2):928-36. doi: 10.1016/s0006-291x(86)80509-5.
Adenylate cyclase in the presence of GTP became active by the addition of cholera toxin irrespective of the presence of glucagon, and under the same condition the Gs of these activated enzymes were good acceptor of an ADP-ribose moiety. On the other hand, the cyclase in the presence of GDP remained inactive with cholera toxin but became active by the further addition of glucagon. However, neither of these Gs served as a cholera toxin substrate. Glucagon reduced an inhibitory action of added GDP for cholera toxin plus GTP-stimulated adenylate cyclase activity but did not for toxin plus GTP-enhanced ADP-ribosylation of Gs. These results demonstrate that Gs-GTP complex formation alone is not sufficient for Gs to serve as a cholera toxin substrate, and suggest an additional GTP binding site responsible for ADP-ribosylation by the toxin. Hormone dependent preferential interaction between the GTP binding site on Gs coupled with adenylate cyclase regulation and membrane-associated nucleoside diphosphate kinase is discussed.
在存在GTP的情况下，无论是否存在胰高血糖素，通过添加霍乱毒素，腺苷酸环化酶都会变得活跃，并且在相同条件下，这些活化酶的Gs是ADP-核糖部分的良好受体。另一方面，在存在GDP的情况下，腺苷酸环化酶与霍乱毒素一起仍保持无活性，但通过进一步添加胰高血糖素而变得活跃。然而，这些Gs都不作为霍乱毒素的底物。胰高血糖素降低了添加的GDP对霍乱毒素加GTP刺激的腺苷酸环化酶活性的抑制作用，但对毒素加GTP增强的Gs的ADP-核糖基化没有作用。这些结果表明，仅Gs-GTP复合物的形成不足以使Gs作为霍乱毒素的底物，并提示存在另一个负责毒素ADP-核糖基化的GTP结合位点。讨论了与腺苷酸环化酶调节相关的Gs上的GTP结合位点与膜相关核苷二磷酸激酶之间的激素依赖性优先相互作用。
