Possible multifunction of glucose transporter. Transport of nicotinamide by reconstituted liposomes.
A kinetic study of the uptake of nicotinamide by reconstituted liposomes containing the human erythrocyte glucose transporter, compared with that of D-glucose, demonstrated that the Km and Vmax. values were almost the same for each compound, and that the uptake of D-glucose was competitively inhibited by nicotinamide. At 20 mM concentration, 2-deoxy-D-glucose, 3-O-methyl-D-glucose and 4,6-O-ethylidene-D-glucose all caused 50% inhibition of nicotinamide uptake, but L-glucose and nicotinic acid were not inhibitory. Similar results were obtained for the uptake of D-glucose. Cytochalasin B binding to the liposomes was inhibited in a dose-dependent manner by either nicotinamide or D-glucose. Antibody for glucose transporter detected in band 4.5 by SDS/PAGE inhibited the uptake of D-glucose and nicotinamide. A possible uptake of nicotinamide by nucleoside transporter was excluded. In human erythrocytes, cytochalasin B binding was inhibited dose-dependently by either nicotinamide or D-glucose, and cytochalasin B depressed the uptake of both nicotinamide and 2-deoxy-D-glucose. These findings were well reproduced in the reconstituted liposomes. The very close similarities between uptake of nicotinamide and D-glucose suggest that the glucose transporter plays a direct role in transport of nicotinamide, which is structurally quite different from monosaccharides, and thus that the transporter is probably multifunctional.
Sofue
M
M
Faculty of Pharmaceutical Sciences, University of Tokushima, Japan.
Yoshimura
Y
Y
Nishida
M
M
Kawada
J
J
D001692:Biological Transport / Q000187:drug effects; D003571:Cytochalasin B / Q000378:metabolism; D004912:Erythrocytes / Q000737:chemistry / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008081:Liposomes; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009536:Niacinamide / Q000378:metabolism*; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology
D008081:Liposomes; D009004:Monosaccharide Transport Proteins; D009536:Niacinamide; D003571:Cytochalasin B; D013868:Thioinosine; C001789:4-nitrobenzylthioinosine; D005947:Glucose