title: Nicotinamide is not a substrate of the facilitative hexose transporter GLUT1.
abstract: 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.
authors.affiliation: Instituto de Bioquímica, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567, Valdivia, Chile. areyes@uach.cl
authors.forename: Alejandro M
authors.initials: AM
authors.lastname: Reyes
authors.forename: Fernando
authors.initials: F
authors.lastname: Bustamante
authors.forename: Coralia I
authors.initials: CI
authors.lastname: Rivas
authors.forename: Marcela
authors.initials: M
authors.lastname: Ortega
authors.forename: Claudia
authors.initials: C
authors.lastname: Donnet
authors.forename: Juan P
authors.initials: JP
authors.lastname: Rossi
authors.forename: Jorge
authors.initials: J
authors.lastname: Fischbarg
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Vera
mesh_terms: D019325:3-O-Methylglucose / Q000097:blood; D000818:Animals; D016466:CHO Cells / Q000378:metabolism; D006224:Cricetinae; D003571:Cytochalasin B / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D003847:Deoxyglucose / Q000097:blood; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D051272:Glucose Transporter Type 1; D006801:Humans; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000097:blood / Q000378:metabolism*; D009536:Niacinamide / Q000097:blood / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D014162:Transfection; D022161:Transport Vesicles / Q000378:metabolism
chemical_list: D005419:Flavonoids; D051272:Glucose Transporter Type 1; D009004:Monosaccharide Transport Proteins; C495677:SLC2A1 protein, human; D019325:3-O-Methylglucose; D009536:Niacinamide; D003571:Cytochalasin B; C040015:myricetin; D003847:Deoxyglucose; D019833:Genistein