title: Human erythrocytes transport dehydroascorbic acid and sugars using the same transporter complex.
abstract: GLUT1, the primary glucose transport protein in human erythrocytes [red blood cells (RBCs)], also transports oxidized vitamin C [dehydroascorbic acid (DHA)]. A recent study suggests that RBC GLUT1 transports DHA as its primary substrate and that only a subpopulation of GLUT1 transports sugars. This conclusion is based on measurements of cellular glucose and DHA equilibrium spaces, rather than steady-state transport rates. We have characterized RBC transport of DHA and 3-O-methylglucose (3-OMG), a transported, nonmetabolizable sugar. Steady-state 3-OMG and DHA uptake in the absence of intracellular substrate are characterized by similar Vmax (0.16 ± 0.01 and 0.13 ± 0.02 mmol·l(-1)·min(-1), respectively) and apparent Km (1.4 ± 0.2 and 1.6 ± 0.7 mM, respectively). 3-OMG and DHA compete for uptake, with Ki(app) of 0.7 ± 0.4 and 1.1 ± 0.1 mM, respectively. Uptake measurements using RBC inside-out-membrane vesicles demonstrate that 3-OMG and DHA compete at the cytoplasmic surface of the membrane, with Ki(app) of 0.7 ± 0.1 and 0.6 ± 0.1 mM, respectively. Intracellular 3-OMG stimulates unidirectional uptake of 3-OMG and DHA. These findings indicate that DHA and 3-OMG bind at mutually exclusive sites at exo- and endofacial surfaces of GLUT1 and are transported via the same GLUT1 complex.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts.
authors.forename: Jay M
authors.initials: JM
authors.lastname: Sage
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts anthony.carruthers@umassmed.edu.
authors.forename: Anthony
authors.initials: A
authors.lastname: Carruthers
mesh_terms: D019325:3-O-Methylglucose / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D001692:Biological Transport; D002250:Carbon Radioisotopes; D003683:Dehydroascorbic Acid / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1 / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D011485:Protein Binding; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D051272:Glucose Transporter Type 1; C495677:SLC2A1 protein, human; D014316:Tritium; D019325:3-O-Methylglucose; D005947:Glucose; D003683:Dehydroascorbic Acid
keywords: GLUT1; dehydroascorbic acid transport; erythrocyte; glucose transport