“Nicotinamide Is Not a Substrate of the Facilitative Hexose Transporter GLUT1”.

REYES, A.M.; BUSTAMANTE, F.; RIVAS, C.; DONNET, C; ROSSI, J.P.F.C.; FISCHBARG, J.; VERA, J.C.

BIOCHEMISTRY

American Chemical Society

Lugar: Vanderbilt; Año: 2002 vol. 41 p. 8075 - 8081

0006-2960

ABSTRACT: It has been proposed that GLUT1, a membrane protein that transports hexoses and the oxidizedform 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 thetransport of 2-deoxy-D-glucose, 3-O-methyl-D-glucose, and nicotinamide in human erythrocytes and rightside-out and inside-out erythrocyte membrane vesicles. The transport of nicotinamide was saturable, witha KM for influx and efflux of 6.1 and 6.2 mM, respectively. We found that transport of the hexoses wasnot competed by nicotinamide in both the erythrocytes and the erythrocyte vesicles. Likewise, the transportof 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 humanerythrocyte membranes but did so in a noncompetitive manner. Using GLUT1-transfected CHO cells, wedemonstrated that increased expression of GLUT1 was paralleled by a corresponding increase in hexosetransport but that there were no changes in nicotinamide transport. Moreover, nicotinamide failed to affectthe transport of hexoses in both control and GLUT1-transfected CHO cells. Therefore, our results indicatesthat GLUT1 does not transport nicotinamide, and we propose instead the existence of other systems forthe translocation of nicotinamide across cell membranes.