Reyes Alejandro M, Bustamante Fernando, Rivas Coralia I, Ortega Marcela, Donnet Claudia, Rossi Juan P, Fischbarg Jorge, Vera Juan Carlos
Instituto de Bioquímica, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567, Valdivia, Chile.
Biochemistry. 2002 Jun 25;41(25):8075-81. doi: 10.1021/bi0256328.
It has been proposed that GLUT1, a membrane protein that transports hexoses and the oxidized form of vitamin C, dehydroascorbic acid, is also a transporter of nicotinamide (Sofue, M., Yoshimura, Y., Nishida, M., and Kawada, J. (1992) Biochem. J. 288, 669-674). To ascertain this, we studied the transport of 2-deoxy-D-glucose, 3-O-methyl-D-glucose, and nicotinamide in human erythrocytes and right-side-out and inside-out erythrocyte membrane vesicles. The transport of nicotinamide was saturable, with a K(M) for influx and efflux of 6.1 and 6.2 mM, respectively. We found that transport of the hexoses was not competed by nicotinamide in both the erythrocytes and the erythrocyte vesicles. Likewise, the transport of nicotinamide was not affected by hexoses or by inhibitors of glucose transport such as cytochalasin B, genistein, and myricetin. On the other hand, nicotinamide blocked the binding of cytochalasin B to human erythrocyte membranes but did so in a noncompetitive manner. Using GLUT1-transfected CHO cells, we demonstrated that increased expression of GLUT1 was paralleled by a corresponding increase in hexose transport but that there were no changes in nicotinamide transport. Moreover, nicotinamide failed to affect the transport of hexoses in both control and GLUT1-transfected CHO cells. Therefore, our results indicates that GLUT1 does not transport nicotinamide, and we propose instead the existence of other systems for the translocation of nicotinamide across cell membranes.
有人提出，葡萄糖转运蛋白1（GLUT1），一种转运己糖和维生素C的氧化形式——脱氢抗坏血酸的膜蛋白，也是烟酰胺的转运体（Sofue, M., Yoshimura, Y., Nishida, M., and Kawada, J. (1992) Biochem. J. 288, 669 - 674）。为了确定这一点，我们研究了2-脱氧-D-葡萄糖、3-O-甲基-D-葡萄糖和烟酰胺在人红细胞以及外翻和内翻红细胞膜囊泡中的转运。烟酰胺的转运是可饱和的，其流入和流出的米氏常数（K(M)）分别为6.1和6.2 mM。我们发现，在红细胞和红细胞囊泡中，己糖的转运不受烟酰胺的竞争。同样，烟酰胺的转运也不受己糖或葡萄糖转运抑制剂如细胞松弛素B、染料木黄酮和杨梅素的影响。另一方面，烟酰胺以非竞争性方式阻断细胞松弛素B与人红细胞膜的结合。使用转染了GLUT1的中国仓鼠卵巢（CHO）细胞，我们证明GLUT1表达的增加与己糖转运的相应增加平行，但烟酰胺转运没有变化。此外，烟酰胺在对照和转染了GLUT1的CHO细胞中均未能影响己糖的转运。因此，我们的结果表明GLUT1不转运烟酰胺，相反，我们提出存在其他烟酰胺跨细胞膜转运的系统。
