PMID:11707435

Citation	Venema, K, Quintero, FJ, Pardo, JM and Donaire, JP (2002) The arabidopsis Na+/H+ exchanger AtNHX1 catalyzes low affinity Na+ and K+ transport in reconstituted liposomes. J. Biol. Chem. 277:2413-8
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.
Links	PubMed Online version:10.1074/jbc.M105043200
Keywords	Arylsulfonates/metabolism; Biological Transport; Blotting, Western; Catalysis; Cations/metabolism; Chlorine/metabolism; Chromatography, Affinity; Chromatography, Ion Exchange; Electrophoresis, Polyacrylamide Gel; Histidine/chemistry; Hydrogen-Ion Concentration; Liposomes/metabolism; Plasmids/metabolism; Potassium/metabolism; Protein Binding; Recombinant Proteins/metabolism; Sodium/metabolism; Sodium-Hydrogen Antiporter/chemistry; Sodium-Hydrogen Antiporter/physiology; Structure-Activity Relationship; Time Factors; Up-Regulation
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