GTP BINDING PROTEINS AND ADENYLATE CYCLASE

霍乱原通过催化腺苷酸环化酶， NAD的存在，Gs α的ADP-核糖基化， 环化酶系统的刺激性GTP结合蛋白。 卡恩和 Gilman（J.Biol.Chem.261，7906-7911（1986））鉴定了另一种 ADP核糖基化因子（ARF）是一种GTP结合蛋白， 刺激了这种反应。 有人提出毒素底物 是ARF-Gs α复合物，且ARF可以具有 在调节Gs α活性中的生理作用。 东盟区域论坛， 从牛脑膜中纯化，不仅增强了 Gs α的ADP核糖基化，但也是Gs α非依赖性的 霍乱反应。 这些是（1）ADP- 胍丁胺的核糖基化反应 化合物;（2）几种蛋白质的ADP-核糖基化 与Gs α无关;和（3）毒素的自身ADP核糖基化 A1肽。 这些反应，以及ADP-核糖基化的 ARF本身受到GTP或稳定的GTP类似物的刺激， 作为鸟苷基-5 '-基亚氨基-β-二磷酸和鸟苷5'-O- ）+（3-硫代-三磷酸）; GDP和鸟苷-5 '-0-（2- 硫代二磷酸盐）无活性。 这些观察结果是一致 结论是ARF直接与A 亚单位的胆固醇在GTP依赖的方式，从而 增强催化活性，表现为ADP-核糖转移 G α和其他蛋白质，毒素A1肽，或 胍丁胺 我们还纯化了另外两种可溶性因子， 增强促胆原对ADP-核糖基化Gs α的能力。 每一种都表现出类似于ARF的性质， 推测ARF样蛋白家族可能存在于 动物细胞

Choleragen activates adenylate cyclase by catalyzing, in the presence of NAD, the ADP-ribosylation of Gs alpha, the stimulatory GTP-binding protein of the cyclase system. Kahn and Gilman (J. Biol. Chem. 261, 7906-7911 (1986)) identified another GTP-binding protein termed ADP-ribosylation factor (ARF) that stimulated this reaction. It was proposed that the toxin substrate is an ARF-Gs alpha complex and that ARF may have a physiological role in regulation of Gs alpha activity. ARF, purified from bovine brain membranes, enhanced not only the ADP-ribosylation of Gs alpha, but also Gs alpha-independent choleragencatalyzed reactions. These are the (1) ADP- ribosylation of agmatine, a low molecular weight guanidino compound; (2) ADP-ribosylation of several of several proteins unrelated to Gs alpha; and (3) auto-ADP-ribosylation of the toxin A1 peptide. These reactions, as well as the ADP-ribosylation of ARF itself, were stimulated by GTP or stable GTP analogues such as guanyl-5'-yl imido-beta gamma-diphosphate and guanosine 5'-0- )+(3-thio-triphosphate); GDP and guanosine-5'-0-(2- thiodiphosphate) were inactive. These observations are consistent with the conclusion that ARF interacts directly with the A subunit of choleragen in a GTP-dependent fashion thereby enhancing catalytic activity manifest as transfer of ADP-ribose to Gs alpha and other proteins, to the toxin A1 peptide, or to agmatine. We have also purified two other soluble factors that enhanced the ability of choleragen to ADP-ribosylate Gs alpha. Each exhibited properties similar to ARF leading to the speculation that a family of ARF-like proteins may exist in animal cells.