Buchs A, Wu L, Morita H, Whitesell R R, Powers A C
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
Endocrinology. 1995 Oct;136(10):4224-30. doi: 10.1210/endo.136.10.7664639.
The glucose transporter in the hepatocyte and pancreatic beta-cell (GLUT 2) has a lower affinity for glucose than other members of the glucose transporter family. To investigate the molecular mechanism for the distinctive affinity of GLUT 2 for glucose, we expressed chimeric GLUT 2 and GLUT 4 proteins in Xenopus oocytes and measured 3-O-methyl-D-glucose transport. In the oocyte system, GLUT 2 had a Km of 31.8 +/- 2.8 mM for 3-O-methyl-D-glucose, whereas GLUT 4 had a Km of 7.2 +/- 2.4 mM under equilibrium exchange conditions. GLUT 4/GLUT 2 chimera that contained the intracellular loop and transmembrane domains 7-12 of GLUT 2 (amino acids 239-497) had a Km similar to that of wild-type GLUT 2. A GLUT 4/GLUT 2 chimera in which the COOH-terminal 30 amino acids of GLUT 4 were replaced with the corresponding region of GLUT 2 had a 2-fold higher Km than GLUT 4, but still had a much lower Km than GLUT 2. These results indicate that both transmembrane domains 7-12 and the COOH-terminus of the protein are responsible for the distinctive glucose affinity of GLUT 2.
肝细胞和胰腺β细胞中的葡萄糖转运蛋白（GLUT 2）对葡萄糖的亲和力低于葡萄糖转运蛋白家族的其他成员。为了研究GLUT 2对葡萄糖独特亲和力的分子机制，我们在非洲爪蟾卵母细胞中表达了嵌合的GLUT 2和GLUT 4蛋白，并测量了3 - O - 甲基 - D - 葡萄糖的转运。在卵母细胞系统中，在平衡交换条件下，GLUT 2对3 - O - 甲基 - D - 葡萄糖的Km为31.8±2.8 mM，而GLUT 4的Km为7.2±2.4 mM。包含GLUT 2的细胞内环和跨膜结构域7 - 12（氨基酸239 - 497）的GLUT 4/GLUT 2嵌合体的Km与野生型GLUT 2相似。一种将GLUT 4的COOH末端30个氨基酸替换为GLUT 2相应区域的GLUT 4/GLUT 2嵌合体的Km比GLUT 4高2倍，但仍比GLUT 2低得多。这些结果表明，蛋白的跨膜结构域7 - 12和COOH末端均对GLUT 2独特的葡萄糖亲和力起作用。
