title: Maltose/proton co-transport in Saccharomyces cerevisiae. Comparative study with cells and plasma membrane vesicles.
abstract: Maltose/proton co-transport was studied in intact cells and in plasma membrane vesicles of the yeast Saccharomyces cerevisiae. In order to determine uphill transport in vesicles, plasma membranes were fused with proteoliposomes containing cytochrome c oxidase as a proton-motive force-generating system. Maltose accumulation, dependent on the electrical and pH gradients, was observed. The initial uptake velocity and accumulation ratio in vesicles proved to be dependent on the external pH. Moreover, kinetic analysis of maltose transport showed that Vmax. values greatly decreased with increasing pH, whereas the Km remained virtually constant. These observations were in good agreement with results obtained with intact cells, and suggest that proton binding to the carrier proceeds with an apparent pK of 5.7. The observation with intact cells that maltose is co-transported with protons in a one-to-one stoichiometry was ascertained in the vesicle system by measuring the balance between proton-motive force and the chemical maltose gradient. These results show that maltose transport in vesicles prepared by fusion of plasma membranes with cytochrome c oxidase proteoliposomes behaves in a similar way as in intact cells. It is therefore concluded that this vesicle model system offers a wide range of new possibilities for the study of maltose/proton co-transport in more detail.
authors.affiliation: Department of Medical Biochemistry, Sylvius Laboratory, Leiden, The Netherlands.
authors.forename: C C
authors.initials: CC
authors.lastname: Van Leeuwen
authors.forename: R A
authors.initials: RA
authors.lastname: Weusthuis
authors.forename: E
authors.initials: E
authors.lastname: Postma
authors.forename: P J
authors.initials: PJ
authors.lastname: Van den Broek
authors.forename: J P
authors.initials: JP
authors.lastname: Van Dijken
mesh_terms: D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D003576:Electron Transport Complex IV / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007785:Lactose / Q000378:metabolism; D008081:Liposomes; D008320:Maltose / Q000378:metabolism*; D008564:Membrane Potentials; D009004:Monosaccharide Transport Proteins; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D027981:Symporters
chemical_list: D002352:Carrier Proteins; D005656:Fungal Proteins; D008081:Liposomes; D009004:Monosaccharide Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D027981:Symporters; C067575:maltose transport system, S cerevisiae; D008320:Maltose; D003576:Electron Transport Complex IV; D007785:Lactose