Al teration of GTP binding proteins coupled with secretory response in rat submandibular tissues

组织短暂暴露于10muM异丙肾上腺素(IPR)，在进一步孵育过程中，对IPR反应的粘蛋白分泌的刺激减少，同时β-肾上腺素受体的数量和它们对β-激动剂的亲和力也减少。用IPR处理组织后，IPR刺激的腺苷环化酶活性降低30%，抑制GTP结合蛋白(GI蛋白)的GTP结合能力增加25%。经IPR处理后，百日咳毒素(IAP)催化组织膜GI蛋白ADP-核糖化的能力增加了60%，而刺激性GTP结合蛋白(Gs蛋白)的功能仅在IPR首次孵育时观察到增强。IPR处理组织中，IAP催化的GI蛋白的ADP-核糖化作用在预先用环磷酸腺苷依赖的蛋白激酶处理时降低，但在预先用碱性磷酸酶处理时显著增加。0.25mM冈田酸对IPR诱导的j4399蛋白分泌脱敏和IAP催化的Gi蛋白ADP-核糖化反应均无明显影响。我们还发现，分泌颗粒膜中存在分子量较大的GTP结合蛋白(G蛋白)，肉毒杆菌毒素具有特异性地催化该蛋白的ADP-重波糖基化的能力。在Mg~(2+)和Gt~(2+)存在下，ATP或GTP-GammaS可刺激淀粉酶从颗粒中释放。颗粒的构象变化也是由这些药物引起的，这表明蛋白质在胞吐作用中的重要性。这些结果表明，Gi蛋白磷酸化的酶修饰在调节细胞对随后的肾上腺素能β-激动剂刺激的反应中是重要的。

Brief exposure of the tissues to 10muM isoproterenol (IPR) resulted in reduced stimulation of mucin secretion in response to IPR during further incubation coupled with the decrease in the number of beta-adrenoceptors and in the affinity of them for beta-agonist. Treatment of the tissues with IPR caused a 30% decrease in IPR-stimulated adenylate cyclase activity and a 25% increase in the GTP binding capacity of inhibitory GTP binding proteins (Gi proteins). This IPR-treatment triggered a 60% increase in the ability of pertussis toxin (IAP) to catalyze ADP-ribosylation of Gi proteins in the tissue membrane Enhanced function of stimulatory GTP binding proteins (Gs proteins) was observed only during the first incubation of the tissues with IPR.The IAP-catalyzed ADP-ribosylation of Gi proteins in the tissues treated with IPR was decreased by prior treatment with cyclic AMP-dependent protein kinase, but was increased markedly by prior treatment with alkaline phosphatase. The IPR-induced desensitization of j4399 protein secretion and increase in the IAP-catalyzed ADP-ribosylation of Gi proteins were not abserved in the tissues pre-treated with 0.25muM okadaic acid. We also found that GTP binding proteins (G proteins) of molecular weight exists in secretory granule membranes and botulinum toxin has an ability specifically to catalyze ADP-rebosylation of this protein. Release of amylase from the granules was stimulated by ATP or GTPgammaS in the presence of Mg^<2+>. The conformational change in the granules was also caused by these agents, suggesting an importance of the protein in exocytosis.These results suggest that enzymatic modification of the phosphorylation of Gi proteins is important in the regulation of cell response to subsequent stimulation by adrenergic beta-agonists.