Xu B, Epstein P N
Department of Pharmacology and Toxicology, University of North Dakota School of Medicine, Grand Forks 58202-9037, USA.
Endocr Res. 1996 May;22(2):147-58. doi: 10.1080/07435809609030504.
Recent reports have proposed that sequence specific interactions between glucokinase and other beta cell proteins are important to glucokinase regulation of beta cell activity. We have previously reported enhancement of beta cell function by a transgenic hexokinase derived from yeast which has only 30% amino acid sequence homology to glucokinase. To test the functional significance of the amino acid sequence of islet glucokinase we have made a quantitative study of the effect of yeast hexokinase on beta cell glucose metabolism and insulin secretion. Transgenic and normal islets were assayed for hexokinase activity, glucose usage and insulin secretion. Most parameters were measured at six glucose concentrations between 0.5 and 20 mM glucose. Transgenic islet hexokinase activity measured in islet extracts exceeded normal islet hexokinase activity by 31 to 77 percent at different glucose concentrations. At all glucose concentrations tested the percentage increase in transgenic glucose metabolism greatly exceeded the percentage increase in transgenic hexokinase activity. The increase in transgenic glucose metabolism produced a proportional reduction in the threshold for glucose stimulated insulin secretion. However, yeast hexokinase had little if any effect on the first phase of insulin secretion. The finding that metabolism was very sensitive to yeast hexokinase but first phase secretion was not, supports recent proposals that hexokinase and glucokinase may be physically and functionally separated in the beta cell.
最近的报道提出，葡萄糖激酶与其他β细胞蛋白之间的序列特异性相互作用对于β细胞活性的葡萄糖激酶调节很重要。我们之前报道过，源自酵母的转基因己糖激酶可增强β细胞功能，该酵母己糖激酶与葡萄糖激酶的氨基酸序列同源性仅为30%。为了测试胰岛葡萄糖激酶氨基酸序列的功能重要性，我们对酵母己糖激酶对β细胞葡萄糖代谢和胰岛素分泌的影响进行了定量研究。对转基因胰岛和正常胰岛进行了己糖激酶活性、葡萄糖利用和胰岛素分泌的检测。大多数参数是在0.5至20 mM葡萄糖之间的六个葡萄糖浓度下测量的。在不同葡萄糖浓度下，胰岛提取物中测得的转基因胰岛己糖激酶活性比正常胰岛己糖激酶活性高出31%至77%。在所有测试的葡萄糖浓度下，转基因葡萄糖代谢的增加百分比大大超过转基因己糖激酶活性的增加百分比。转基因葡萄糖代谢的增加使葡萄糖刺激胰岛素分泌的阈值成比例降低。然而，酵母己糖激酶对胰岛素分泌的第一阶段几乎没有影响。代谢对酵母己糖激酶非常敏感但第一阶段分泌不敏感这一发现，支持了最近关于己糖激酶和葡萄糖激酶在β细胞中可能在物理和功能上分离的提议。
