Qualitative change of GTP-binding protein.

为了了解抑制gtp结合(G)蛋白在体外的质变，我们用百日毒（胰岛激活蛋白，IAP）对Gi蛋白进行了腺苷基化，并对3个α - β - γ -亚基的三聚体解离成α -亚基和β - γ -亚基进行了实验，并使用Gi蛋白抗体进行了western blot。在该蛋白上添加锂离子后，血小板膜内IAP对Gi蛋白的自旋基化量减少，活化的Gi蛋白对腺苷酸环化酶活性的抑制作用减弱，但3个亚基的解离没有改变。此外，用碳酸锂慢性治疗躁狂抑郁症患者可降低血小板膜中IAP的ADPribosylation量。然后研究了环amp依赖性蛋白激酶对部分纯化的gi蛋白的磷酸化作用。在上述实验条件下，Western blot显示Gi蛋白在上述实验条件下未发生明显的定量变化。结果表明，在上述实验条件下，Gi蛋白的adp -核糖基化量减少，分化的HL-60细胞中，Gi蛋白被活化后的磷脂酶C活性降低，Mg2+和GTPgamma s诱导的三个亚基解离受到抑制。结果表明，gi蛋白的质变在跨膜信号转导调控中具有生理和病理功能。

In order to know the qualitative changes of inhibitory GTPbinding(G)protein in vitro, we did ADP-ribosylation of Gi protein by pertussis toxin(islet-activating protein, IAP), an experiment about dissociation of the trimer of the three alpha beta gamma-subunits into alpha -subunits and beta gamma -subunits and western blot using an antibody for Gi-protein. The addition with lithium ion to the protein caused a decrease of the amounts of ADPribosylation of Gi protein by IAP in human platelet membranes and weekened the inhibition'of adenylate cyclase activity by activated Gi-protein, though the dissociation of the three subunits did not change. Also, chronic treatment of manic depressive patients with lithium carbonate decreased the amounts of ADPribosylation by IAP in their platelet membranes. Next the effect of phosphorylation of partially purified Gi-protein by cyclic AMP-dependent protein kinase was studied. The treatment caused a decrease of the amounts of ADP-ribosylation of Gi protein by IAP in human platelet membranes, weekened the phospholipase C activity by activated Gi-protein in differentiated HL-60 cells and inhibited the dissociation of the three subunits induced by Mg2+ and GTPgamma S. Western blot showed no remarkable quantitative changes in Gi protein in the experimental conditions mentioned above. The results strongly suggested that the qualitative changes of Gi-proteins are physiologically and pathologically functional in the regulation of transmembrane signal transduction.