title: Characterization of solute transport in plasma membrane vesicles isolated from cotyledons ofRicinus communis L. : II. Evidence for a proton-coupled mechanism for sucrose and amino acid uptake.
abstract: Evidence is presented for the proton-coupled transport of sucrose and glutamine in purified plasma membrane vesicles isolated from cotyledons ofRicinus communis. Imposition of a pH gradient (internal alkaline) across the plasma membrane resulted in a rapid uptake of sucrose and glutamine which was inhibited in the presence of carbonyl cyanide-m-chlorophenyl hydrazone. Imposition of a pH gradient plus an internal negative membrane potential stimulated uptake further. Glucose and fructose uptakes were negligible under these conditions. Sucrose uptake into the vesicles demonstrated saturation kinetics with a Km of 0.87 mol·m(-3), indicating carrier-mediated transport. In support of this, uptake was very sensitive to the protein-modifying reagentp-chloromercuribenzenesulphonic acid. N-Ethylmaleimide, another sulphydryl reagent, was only slightly inhibitory. However, both reagents strongly inhibited sucrose uptake into intact cotyledons; the possible reasons for the difference between the intact and isolated systems are assessed. The value of this system for the study of sucrose and amino acid carriers is discussed.
authors.affiliation: Department of Biology, University of Southampton, SO9 5NH, Southampton, UK.
authors.forename: L E
authors.initials: LE
authors.lastname: Williams
authors.forename: S J
authors.initials: SJ
authors.lastname: Nelson
authors.forename: J L
authors.initials: JL
authors.lastname: Hall