GLUCOSE-TRANSPORTER ISOFORMS GLUT1 AND GLUT3 TRANSPORT DEHYDROASCORBIC ACID

Dehydroascorbic acid (DHA) is rapidly taken up by cells and reduced to ascorbic acid (AA). Using the Xenopus laevis oocyte expression system we examined transport of DHA and AA via glucose transporter isoforms GLUT1-5 and SGLT1, The apparent K-m of DHA transport via GLUT1 and GLU T3 was 1.1 +/- 0.2 and 1.7 +/- 0.3 mM, respectively, High performance liquid chromatography analysis confirmed 100% reduction of DHA to AA w ithin oocytes, GLUT4 transport of DHA was only 2-4-fold above control and transport kinetics could not be calculated, GLUT2, GLUT5, and SGLT 1 did not transport DHA and none of the isoforms transported AA. Radio labeled sugar transport confirmed transporter function and identity of all cDNA clones was confirmed by restriction fragment mapping. GLUT1 and GLUT3 cDNA were further verified by polymerase chain reaction, DHA transport activity in both GLUT1 and GLUT3 was inhibited by 2-deoxygl ucose, D-glucose, and S-O-methylglucose among other hexoses while fruc tose and L-glucose showed no inhibition, Inhibition by the endofacial inhibitor, cytochalasin B, was non-competitive and inhibition by the e xofacial inhibitor, 4,6-O-ethylidene-alpha-glucose, was competitive. E xpressed mutant constructs of GLUT1 and GLUT3 did not transport DHA. D HA and a-deoxyglucose uptake by Chinese hamster ovary cells overexpres sing either GLUT1 or GLUT3 was increased 2-8 fold over control cells. These studies suggest GLUT1 and GLUT3 isoforms are the specific glucos e transporter isoforms which mediate DHA transport and subsequent accu mulation of AA.