title: NapA Na(+)/H(+) Antiporter as a Sodium Extrusion System Supplementary to the Vacuolar Na(+)-ATPase in Enterococcus hirae.
abstract: Enterococcus hirae has two sodium extrusion systems: the NapA Na(+)/H(+) antiporter and the vacuolar Na(+)-ATPase. We found that a NapA mutant, WD4, which is deficient in Na(+)/H(+) antiporter activity, grew well in the pH range of 6 to 10 up to 200 mM sodium. This was due to active, potential-independent sodium extrusion by the Na(+)-ATPase, which was induced under these conditions. The NapA Na(+)/H(+) antiporter is thus not a prerequisite for growth of E. hirae in the presence of sodium, but plays a supplementary role in sodium extrusion at acidic pH.
authors.affiliation: a Faculty of Pharmaceutical Sciences, Chiba University.
authors.forename: M
authors.initials: M
authors.lastname: Kawano
authors.affiliation: a Faculty of Pharmaceutical Sciences, Chiba University.
authors.forename: K
authors.initials: K
authors.lastname: Igarashi
authors.affiliation: b Department of Clinical Pharmacology, University of Berne.
authors.forename: M
authors.initials: M
authors.lastname: Solioz
authors.affiliation: a Faculty of Pharmaceutical Sciences, Chiba University.
authors.forename: Y
authors.initials: Y
authors.lastname: Kakinuma
keywords: Enterococcus hirae; Na+/H+ antiporter; NapA; sodium extrusion; vacuolar Na+-ATPase