Qualitative change of GTP-binding protein.

为了了解抑制性GTP结合（G）蛋白在体外的质的变化，我们用百日咳毒素（IAP）对Gi蛋白进行了ADP-核糖基化，进行了三个α-β-γ亚基的三聚体解离为α-亚基和β-γ亚基的实验，并用Gi蛋白抗体进行了westernblot。锂离子使人血小板膜上IAP对Gi蛋白的腺苷三磷酸化量减少，使活化的Gi蛋白对腺苷酸环化酶活性的抑制减弱，但对三个亚基的解离无影响。此外，躁狂抑郁症患者的碳酸锂长期治疗减少了血小板膜中IAP的AD Pribosylation量。接下来，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。结果表明，该处理可使人血小板膜上ADP核糖基化的Gi蛋白减少，使分化的HL-60细胞中激活的Gi蛋白的磷脂酶C活性降低，并抑制Mg ~（2+）和GTP γ S诱导的三种亚基的解离。Western blot结果显示，在上述实验条件下，Gi蛋白的表达量无明显变化。结果表明，Gi-protein的质的变化在跨膜信号转导的调节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.