Bánhegyi G, Marcolongo P, Burchell A, Benedetti A
Istituto di Patologia Generale, Università di Siena, Siena, 53100, Italy.
Arch Biochem Biophys. 1998 Nov 1;359(1):133-8. doi: 10.1006/abbi.1998.0888.
Glucose transport across the membrane of rat liver microsomal vesicles was studied by a rapid filtration method in three different experimental systems: (i) inward transport in the presence of extravesicular glucose, (ii) efflux from passively preloaded vesicles, and (iii) efflux of glucose generated intravesicularly by glucose-6-phosphatase upon addition of glucose 6-phosphate were investigated. The apparent intravesicular glucose space estimated with the rapid filtration method was lower than the total microsomal glucose accessible space both the in the steady-state phase of uptake and at the starting point of efflux: 0.5 versus 2.3 microl/mg protein. The initial rate of influx/efflux was dependent on the extravesicular/intravesicular glucose concentration and was much lower than the rate of influx estimated previously by the light-scattering technique. Both influx and efflux could be inhibited by N-ethylmaleimide and possibly became saturable at high (>100 mM) glucose concentration. Known inhibitors of GLUT transporters (genistein, cytochalasin B, phloretin, and hexoses) did not affect glucose influx. The time course of glucose efflux from vesicles preincubated in the presence of glucose 6-phosphate was similar to that from glucose-loaded vesicles. These data together with that obtained previously (by a light-scattering technique; Marcolongo, P., Fulceri, R., Giunti, R., Burchell, A., and Benedetti, A. (1996) Biochem. Biophys. Res. Commun. 219, 916-922) indicate that microsomal vesicles are heterogeneous regarding their glucose-transporting properties and that glucose transport is bidirectional and its feature meets the requirements of a facilitative transport.
采用快速过滤法，在三种不同的实验系统中研究了葡萄糖跨大鼠肝微粒体囊泡膜的转运：（i）在囊泡外葡萄糖存在下的内向转运；（ii）来自被动预加载囊泡的流出；（iii）添加葡萄糖 6 - 磷酸后，由葡萄糖 - 6 - 磷酸酶在囊泡内产生的葡萄糖的流出。用快速过滤法估算的囊泡内葡萄糖表观空间在摄取的稳态阶段和流出起始点均低于总微粒体可及葡萄糖空间：分别为 0.5 与 2.3 微升/毫克蛋白质。流入/流出的初始速率取决于囊泡外/囊泡内葡萄糖浓度，且远低于先前通过光散射技术估算的流入速率。流入和流出均可被 N - 乙基马来酰亚胺抑制，并且在高（>100 mM）葡萄糖浓度下可能达到饱和。已知的 GLUT 转运蛋白抑制剂（染料木黄酮、细胞松弛素 B、根皮素和己糖）不影响葡萄糖流入。在葡萄糖 6 - 磷酸存在下预孵育的囊泡中葡萄糖流出的时间进程与葡萄糖加载囊泡的相似。这些数据以及先前获得的数据（通过光散射技术；Marcolongo，P.，Fulceri，R.，Giunti，R.，Burchell，A.和 Benedetti，A.（1996）Biochem. Biophys. Res. Commun. 219，916 - 922）表明，微粒体囊泡在其葡萄糖转运特性方面是异质的，并且葡萄糖转运是双向的，其特性符合易化转运的要求。
