title: Characterisation of glucose transport in Saccharomyces cerevisiae with plasma membrane vesicles (countertransport) and intact cells (initial uptake) with single Hxt1, Hxt2, Hxt3, Hxt4, Hxt6, Hxt7 or Gal2 transporters.
abstract: The yeast glucose transporters Hxt1, Hxt2, Hxt3, Hxt4, Hxt6, Hxt7 and Gal2, individually expressed in an hxt1-7 null mutant strain, demonstrate the phenomenon of countertransport. Thus, these transporters, which are the most important glucose transporters in Saccharomyces cerevisiae, are facilitated diffusion transporters. Apparent K(m)-values from high to low affinity, determined from countertransport and initial-uptake experiments, respectively, are: Hxt6 0.9+/-0.2 and 1.4+/-0.1 mM, Hxt7 1.3+/-0.3 and 1.9+/-0.1 mM, Gal2 1.5 and 1.6+/-0.1 mM, Hxt2 2.9+/-0.3 and 4.6+/-0.3 mM, Hxt4 6.2+/-0.5 and 6.2+/-0.3 mM, Hxt3 28.6+/-6.8 and 34.2+/-3.2 mM, and Hxt1 107+/-49 and 129+/-9 mM. From both independent methods, countertransport and initial uptake, the same range of apparent K(m)-values was obtained for each transporter. In contrast to that in human erythrocytes, the facilitated diffusion transport mechanism of glucose in yeast was symmetric. Besides facilitated diffusion there existed in all single glucose transport mutants, except for the HXT1 strain, significant first-order behaviour.
authors.affiliation: Department of Pharmacology and Toxicology, Philipps-University, D-35033 Marburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Maier
authors.forename: Bernhard
authors.initials: B
authors.lastname: Völker
authors.forename: Eckhard
authors.initials: E
authors.lastname: Boles
authors.forename: Günter Fred
authors.initials: GF
authors.lastname: Fuhrmann
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D005800:Genes, Fungal; D005947:Glucose / Q000378:metabolism*; D051246:Glucose Transport Proteins, Facilitative; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism
chemical_list: C106901:GAL2 protein, S cerevisiae; D051246:Glucose Transport Proteins, Facilitative; C084498:HXT2 protein, S cerevisiae; C090595:HXT3 protein, S cerevisiae; C090593:HXT4 protein, S cerevisiae; C466910:HXT5 protein, S cerevisiae; C095258:HXT7 protein, S cerevisiae; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D005947:Glucose