title: Reconstitution of the hexose phosphate translocator from the envelope membranes of wheat endosperm amyloplasts.
abstract: Amyloplasts were isolated and purified from wheat endosperm and the envelope membranes reconstituted into liposomes. Envelope membranes were solubilized in n-octyl beta-D-glucopyranoside and mixed with liposomes supplemented with 5.6 mol% cholesterol to produce proteoliposomes of defined size, which showed negligible leakage of internal substrates. Transport experiments with proteoliposomes revealed a counter-exchange of glucose 1-phosphate (Glc1P), glucose 6-phosphate (Glc6P), inorganic phosphate (Pi), 3-phosphoglycerate and dihydroxyacetone phosphate. The Glc1P/Pi counter-exchange reaction exhibited an apparent K(m) for Glc1P of 0.4 mM. Glc6P was a competitive inhibitor of Glc1P transport (Ki 0.8 mM), and the two hexose phosphates could exchange with each other, indicating the operation of a single carrier protein. Glc1P/Pi antiport in proteoliposomes showed an exchange stoichiometry at pH 8.0 of 1 mol of phosphate transported per mol of sugar phosphate.
authors.affiliation: School of Biological Sciences, University of Manchester, U.K.
authors.forename: I J
authors.initials: IJ
authors.lastname: Tetlow
authors.forename: C G
authors.initials: CG
authors.lastname: Bowsher
authors.forename: M J
authors.initials: MJ
authors.lastname: Emes
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D004099:Dihydroxyacetone Phosphate / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D005958:Glucosephosphates / Q000378:metabolism; D005988:Glyceric Acids / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000302:isolation & purification* / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D011510:Proteolipids / Q000378:metabolism; D012639:Seeds; D014908:Triticum / Q000378:metabolism*
chemical_list: D005958:Glucosephosphates; D005988:Glyceric Acids; D008081:Liposomes; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D010710:Phosphates; D011510:Proteolipids; C020485:proteoliposomes; D019298:Glucose-6-Phosphate; D004099:Dihydroxyacetone Phosphate; C005156:3-phosphoglycerate; C031590:glucose-1-phosphate