title: The arabidopsis Na+/H+ exchanger AtNHX1 catalyzes low affinity Na+ and K+ transport in reconstituted liposomes.
abstract: In saline environments, plants accumulate Na(+) in vacuoles through the activity of tonoplast Na(+)/H(+) antiporters. The first gene for a putative plant vacuolar Na(+)/H(+) antiporter, AtNHX1, was isolated from Arabidopsis and shown to increase plant tolerance to NaCl. However, AtNHX1 mRNA was up-regulated by Na(+) or K(+) salts in plants and substituted for the homologous protein of yeast to restore tolerance to several toxic cations. To study the ion selectivity of the AtNHX1 protein, we have purified a histidine-tagged version of the protein from yeast microsomes by Ni(2+) affinity chromatography, reconstituted the protein into lipid vesicles, and measured cation-dependent H(+) exchange with the fluorescent pH indicator pyranine. The protein catalyzed Na(+) and K(+) transport with similar affinity in the presence of a pH gradient. Li(+) and Cs(+) ions were also transported with lower affinity. Ion exchange by AtNHX1 was inhibited 70% by the amiloride analog ethylisopropyl-amiloride. Our data indicate a role for intracellular antiporters in organelle pH control and osmoregulation.
authors.affiliation: Departamento de Bioquimica, Biologia Celular y Molecular de Plantas, Estación Experimental del Zaidin, CSIC, Apartado 419, 18080 Granada, Spain.
authors.forename: Kees
authors.initials: K
authors.lastname: Venema
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Quintero
authors.forename: Jose M
authors.initials: JM
authors.lastname: Pardo
authors.forename: Juan Pedro
authors.initials: JP
authors.lastname: Donaire
mesh_terms: D001190:Arylsulfonates / Q000378:metabolism; D001692:Biological Transport; D015153:Blotting, Western; D002384:Catalysis; D002412:Cations / Q000378:metabolism; D002713:Chlorine / Q000378:metabolism; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D006639:Histidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000502:physiology*; D013329:Structure-Activity Relationship; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D001190:Arylsulfonates; D002412:Cations; D008081:Liposomes; D011994:Recombinant Proteins; D017923:Sodium-Hydrogen Exchangers; D006639:Histidine; D002713:Chlorine; D012964:Sodium; C005047:pyranine; D011188:Potassium