Anchors J M, Haggerty D F, Karnovsky M L
J Biol Chem. 1977 Oct 25;252(20):7035-41.
Glucose-6-phosphatase (glucose-6-phosphohydrolase and its associated phosphotransferase activities) was determined in brain tissue and in several preparations derived from brain tissue. These included purified capillaries and established cell lines of neuronal or glial origin. Since it has been suggested that glucose-6-phosphatase may be involved in sugar transport, the characteristics of that process were examined in these preparations. The pattern of uptake of 2-deoxy-D-glucose in four cell lines was shown to involve transport of the analog across the cell membrane that was more rapid than the subsequent phosphorylation of the sugar in the intracellular compartment. In the remaining cell lines and in purified capillaries, phosphorylation of 2-deoxy-D-glucose was at least as rapid as uptake. No differences could be found between the cells in these two categories with respect to amount or localization of glucose-6-phosphatase, ability to phosphorylate 3-O-methyl-D-glucose, or ability to phosphorylate extracellular and intracellular 2-deoxy-D-glucose. In the course of these experiments, it was found that there was a rapid efflux of 2-deoxy-D-glucose from cells that had taken up this sugar. The efflux involves a dephosphorylation step catalyzed by intracellular phosphatase that releases free sugar in the cytoplasm. Glucose-6-phosphatase thus probably has no major role in the phosphorylation of glucose in brain cells, but acts in the more conventional sense, i.e. as a phosphohydrolase.
在脑组织以及从脑组织获得的几种制剂中测定了葡萄糖-6-磷酸酶（葡萄糖-6-磷酸水解酶及其相关的磷酸转移酶活性）。这些制剂包括纯化的毛细血管以及源自神经元或神经胶质细胞的已建立细胞系。由于有人提出葡萄糖-6-磷酸酶可能参与糖转运，因此在这些制剂中研究了该过程的特性。结果表明，四种细胞系中2-脱氧-D-葡萄糖的摄取模式涉及该类似物跨细胞膜的转运，其速度比随后在细胞内区室中糖的磷酸化更快。在其余的细胞系和纯化的毛细血管中，2-脱氧-D-葡萄糖的磷酸化至少与摄取一样快。在这两类细胞之间，在葡萄糖-6-磷酸酶的量或定位、磷酸化3-O-甲基-D-葡萄糖的能力或磷酸化细胞外和细胞内2-脱氧-D-葡萄糖的能力方面均未发现差异。在这些实验过程中，发现摄取了这种糖的细胞中2-脱氧-D-葡萄糖有快速外流。这种外流涉及由细胞内磷酸酶催化的去磷酸化步骤，该步骤在细胞质中释放游离糖。因此，葡萄糖-6-磷酸酶可能在脑细胞中葡萄糖的磷酸化过程中没有主要作用，而是在更传统的意义上起作用，即作为磷酸水解酶。
