title: Overproduction and purification of a functional Na+/H+ antiporter coded by nhaA (ant) from Escherichia coli.
abstract: A Na+/H+ antiporter coded by the nhaA (ant) gene of Escherichia coli has been overproduced and purified. The amino-terminal sequence of the protein has been determined and shown to correlate with initiation at a GUG codon, 75 bases upstream from the previously suggested AUG initiation codon. The purified protein, when reconstituted into proteoliposomes, has Na+/H+ antiport activity. It can mediate sodium uptake when a transmembrane pH gradient is applied. Downhill sodium efflux is shown to be highly dependent on pH and is accelerated by a transmembrane pH gradient. An imposed membrane potential negative inside accelerates Na+ efflux at all pH values tested. These findings suggest that the antiporter is electrogenic both at acid and alkaline pH. The activation at alkaline pH values (2000-fold increase) is consistent with the proposed role of the antiporter in regulation of internal pH at the alkaline pH range.
authors.affiliation: Institute of Life Sciences, Hebrew University, Jerusalem, Israel.
authors.forename: D
authors.initials: D
authors.lastname: Taglicht
authors.forename: E
authors.initials: E
authors.lastname: Padan
authors.forename: S
authors.initials: S
authors.lastname: Schuldiner
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D003062:Codon / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes; D008969:Molecular Sequence Data; D010957:Plasmids; D011510:Proteolipids / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D003062:Codon; D008081:Liposomes; D011510:Proteolipids; D017923:Sodium-Hydrogen Exchangers; C020485:proteoliposomes; D012964:Sodium