McMahon R J, Frost S C
Department of Biochemistry and Molecular Biology, University of Florida, Gainesville 32610, USA.
Am J Physiol. 1996 Apr;270(4 Pt 1):E640-5. doi: 10.1152/ajpendo.1996.270.4.E640.
In 3T3-L1 adipocytes, the glycosylation of the GLUT-1 transporter is altered beyond 12 h of glucose deprivation. To determine whether glycogen degradation provides substrate for normal protein glycosylation during this delay, we measured the glycogen content of 3T3-L1 adipocytes. From an initial value of 0.537 +/- 0.097 mumol glucose/10(6) cells, glycogen was depleted in a time-dependent manner in response to glucose deprivation, exhibiting a half-time of 6 h. Surprisingly, fructose did not prevent glycogen depletion. However, in such glycogen-depleted adipocytes, the alteration of GLUT-1 glycosylation in response to glucose deprivation was more rapid than in normal adipocytes. Chinese hamster ovary (CHO) cells, which synthesize abbreviated dolichol-linked oligosaccharides within minutes of glucose deprivation (J. I. Rearick, A. Chapman, and S. Kornfeld. J. Biol. Chem. 256: 6255-6261, 1981), contained only 1% of the level of glycogen found in 3T3-L1 adipocytes. Glycosylation of GLUT-1 was altered in CHO cells within 3 h of glucose deprivation. These data demonstrate that, during glucose stress, glycogen may serve as a buffer for oligosaccharide biosynthesis and provide a potential explanation for varying sensitivities of different cell types to glucose deprivation.
在3T3-L1脂肪细胞中，葡萄糖剥夺超过12小时后，葡萄糖转运蛋白1（GLUT-1）的糖基化会发生改变。为了确定在这段延迟期间糖原降解是否为正常蛋白质糖基化提供底物，我们测量了3T3-L1脂肪细胞的糖原含量。糖原从初始值0.537±0.097 μmol葡萄糖/10⁶个细胞开始，随着葡萄糖剥夺呈时间依赖性减少，半衰期为6小时。令人惊讶的是，果糖并不能阻止糖原的消耗。然而，在这种糖原耗尽的脂肪细胞中，葡萄糖剥夺引起的GLUT-1糖基化改变比正常脂肪细胞更快。中国仓鼠卵巢（CHO）细胞在葡萄糖剥夺几分钟内就合成缩短的多萜醇连接寡糖（J.I.里里克、A.查普曼和S.科恩菲尔德。《生物化学杂志》256:6255 - 6261,1981），其糖原水平仅为3T3-L1脂肪细胞中糖原水平的1%。葡萄糖剥夺3小时内，CHO细胞中GLUT-1的糖基化就发生了改变。这些数据表明，在葡萄糖应激期间，糖原可能作为寡糖生物合成的缓冲剂，并为不同细胞类型对葡萄糖剥夺的不同敏感性提供了一个潜在的解释。
