Sofue M, Yoshimura Y, Nishida M, Kawada J
Faculty of Pharmaceutical Sciences, University of Tokushima, Japan.
Biochem J. 1993 Jun 15;292 ( Pt 3)(Pt 3):877-81. doi: 10.1042/bj2920877.
Modification of function of the glucose transporter by nucleotides was studied by using liposomes reconstituted with the human erythrocyte glucose transporter. ADP enclosed in the liposomes inhibited the uptake of D-glucose and nicotinamide in a dose-dependent manner, but other enclosed nucleotides (ATP, AMP, CDP, GDP, UDP) showed no effect on the uptake of both. Only intraliposomal ADP was effective, and extra-liposomal ADP was not, under our experimental conditions. Intraliposomal ADP did not change Km, but decreased Vmax to approximately one-third of control for uptake of both D-glucose and nicotinamide. However, the binding and the affinity of cytochalasin B to the reconstituted liposomes were not affected by intraliposomal ADP. The uptake of uridine was not changed in the presence of ADP, indicating that the nucleoside transporter co-existing in the liposomal membranes is not regulated by ADP. Human erythrocytes whose intracellular ATP was decreased by Ca2+ ionophore A23187 also showed decreased uptake of 2-deoxy-D-glucose and nicotinamide. This phenomenon was very similar to that found in the liposomes. These findings suggest the possibility that the function of the glucose transporter is directly and negatively modified by an increased concentration of intracellular ADP.
利用重组有人红细胞葡萄糖转运蛋白的脂质体，研究了核苷酸对葡萄糖转运蛋白功能的修饰作用。脂质体内包裹的ADP以剂量依赖的方式抑制D-葡萄糖和烟酰胺的摄取，但其他包裹的核苷酸（ATP、AMP、CDP、GDP、UDP）对两者的摄取均无影响。在我们的实验条件下，只有脂质体内的ADP有效，而脂质体外的ADP无效。脂质体内的ADP不会改变Km，但会使D-葡萄糖和烟酰胺摄取的Vmax降低至对照的约三分之一。然而，细胞松弛素B与重组脂质体的结合及亲和力不受脂质体内ADP的影响。在ADP存在的情况下，尿苷的摄取没有变化，表明脂质体膜中共存的核苷转运蛋白不受ADP调节。经Ca2+离子载体A23187处理使细胞内ATP减少的人红细胞，其2-脱氧-D-葡萄糖和烟酰胺的摄取也减少。这种现象与在脂质体中发现的非常相似。这些发现提示，细胞内ADP浓度升高可能直接对葡萄糖转运蛋白的功能产生负性修饰作用。
