title: Proton-symport of L-valine in plasma membrane vesicles isolated from leaves of the wild-type and the Val(r)-2 mutant of Nicotiana tabacum L.
abstract: Transport of amino acids across the plasma membranes of various cell types is a key process in controlling the nitrogen balance of leaves. We studied the transport of the neutral amino acid L-valine into plasma membrane vesicles obtained by aqueous polymer two-phase partitioning of a microsomal fraction isolated from leaves of the wild-type and the Val(r)-2 mutant of tobacco (Nicotiana tabacum L.). Initial influxes were determined after the imposition of a pH-gradient (DeltapH, inside alkaline) and/or an electrical gradient (Deltapsi, inside negative) across the vesicle membrane. The initial magnitudes of the imposed gradients were DeltapH=2 and Deltapsi=-68 mV. In vesicles from the wild-type, the DeltapH-dependent valine influx could be analysed into a high-affinity (Km approximately 20 microM) and a low-affinity (Km approximately 3 mM) component. The influx of valine by the low-affinity system was stimulated about twofold, and that by the high-affinity system more than sixfold by the imposition of Deltapsi. This strong stimulation of the high-affinity system may indicate that it transports 2H+/amino acid. In the Val(r)-2 mutant the high-affinity component appeared to be completely absent.
authors.affiliation: Transport Physiology Research Group, Plant Sciences, Utrecht University, Sorbonnelaan 16, NL-3584 CA Utrecht, The Netherlands. a.c.borstlap@bio.uu.nl
authors.forename: A C
authors.initials: AC
authors.lastname: Borstlap
authors.forename: J A
authors.initials: JA
authors.lastname: Schuurmans
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D003576:Electron Transport Complex IV / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D008861:Microsomes / Q000378:metabolism; D009154:Mutation; D009245:NADH Dehydrogenase / Q000378:metabolism; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D010947:Plants, Toxic; D013997:Time Factors; D014026:Nicotiana / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D014633:Valine / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D010940:Plant Proteins; D002734:Chlorophyll; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D000251:Adenosine Triphosphatases; C070990:vanadate-sensitive ATPase; D014633:Valine