title: Evidence for Na(+) influx via the NtpJ protein of the KtrII K(+) uptake system in Enterococcus hirae.
abstract: The ntpJ gene, a cistron located at the tail end of the vacuolar-type Na(+)-ATPase (ntp) operon of Enterococcus hirae, encodes a transporter of the KtrII K(+) uptake system. We found that K(+) accumulation in the ntpJ-disrupted mutant JEM2 was markedly enhanced by addition of valinomycin at pH 10. Studies of the membrane potential (DeltaPsi; inside negative) by 3, 3'-dihexyloxacarbocyanine iodide fluorescence revealed that the DeltaPsi was hyperpolarized at pH 10 in JEM2; the DeltaPsi values of the parent strain ATCC 9790 and JEM2, estimated by determining the equilibrium distribution of K(+) or Rb(+) in the presence of valinomycin, were -118 and -160 mV, respectively. DeltaPsi generation at pH 10 was accomplished by an electrogenic Na(+) efflux via the Na(+)-ATPase, whose levels in the two strains were quite similar. Na(+) uptake driven by an artificially imposed DeltaPsi (inside negative) was missing in JEM2, suggesting that NtpJ mediates Na(+) movement in addition to K(+) movement. Finally, the growth of JEM2 arrested in K(+)-limited high-Na(+) medium at pH 10 was restored by addition of valinomycin. These results suggest that NtpJ mediates electrogenic transport of K(+) as well as Na(+), that it likely mediates K(+) and Na(+) cotransport, and that Na(+) movement via NtpJ is the major Na(+) reentry pathway at high pH values.
authors.affiliation: Faculty of Pharmaceutical Sciences, Chiba University, Inage-ku, Chiba 263-8522, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kawano
authors.forename: R
authors.initials: R
authors.lastname: Abuki
authors.forename: K
authors.initials: K
authors.lastname: Igarashi
authors.forename: Y
authors.initials: Y
authors.lastname: Kakinuma
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D002463:Cell Membrane Permeability / Q000187:drug effects; D016764:Cell Polarity / Q000187:drug effects; D016983:Enterococcus / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D007476:Ionophores; D008565:Membrane Proteins; D014634:Valinomycin; D012964:Sodium; D000251:Adenosine Triphosphatases; C098928:NtpJ protein, bacteria; D025262:Vacuolar Proton-Translocating ATPases; C021838:sodium-translocating ATPase; D006180:Proton-Translocating ATPases; D011188:Potassium