Signal transduction in hepatocytes-Long-term alcohol effects on small G-proteins

ADP-核糖基化是一种翻译后蛋白质修饰，其进而改变哺乳动物细胞中的几种调节蛋白。我们证明，长期酒精摄入增强了大鼠肝细胞膜中58 kDa蛋白的ADP-核糖基化。为了评估这一现象的生物学意义，我们通过两个连续的制备型HPLC从溶解的大鼠肝匀浆中部分纯化了58 kDa受体蛋白。测序结果表明，该酶为磷酸葡萄糖变位酶（EC 5，4，2，2）。该酶自身的ADP核糖基化可以忽略不计，但加入大鼠肝质膜后，ADP核糖基化显著增加。增加的程度是更大的酒精喂养的大鼠比在配对喂养的控制，这表明增强酶活性对ADP-核糖基化磷酸葡萄糖变位酶慢性饮酒后。几种重要的酶被ADP核糖基化，之后它们的活性被改变。这项研究的结果表明，磷酸葡萄糖变位酶是一种新的底物ADP-核糖基化在肝脏和ADP-核糖基化增加后，慢性饮酒。鉴于磷酸葡萄糖变位酶在肝脏中的多种作用（碳水化合物代谢和Ca^2+稳态），这种修饰在酒精对肝细胞影响方面的具体作用可能值得进一步研究。

ADP-ribosylation is a post-translational protein modification which in turn alters several regulatory proteins in mammalian cells. We demonstrated that long-term alcohol intake enhanced the ADP-ribosylation of a 58kDa protein in rat liver plasma membranes. To assess the biological significance of this phenomenon, we partially purified the 58kDa acceptor protein from solubilized rat liver homogenates by two sequential preparative HPLCs. Microsequencing revealed that it was phosphoglucomutase (EC 5,4,2,2). This enzyme underwent negligible auto ADP-ribosylation, but the ADP-ribosylation was remarkably increased by adding rat liver plasma membrances. The extent of the increase was greater in alcohol-fed rats than in pair-fed controls, suggesting enhanced enzyme activities toward ADP-ribosylation of phosphoglucomutase after chronic alcohol consumption. Several important enzymes are ADP-ribosylated, after which their activities are modified. The results of this study showed that phosphoglucomutase is a novel substrate for ADP-ribosylation in the liver and that the ADP-ribosylation is increased after chronic alcohol consumption. In view of the variety of roles of phosphoglucomutase in the liver (carbohydrate metabolism and Ca^<2+>homeostasis), specific roles of this modification in terms of alcohol effects on hepatocytes may deserve further investigation.