Affiliation:
1. Faculty of Pharmaceutical Sciences, Chiba University, Inage-ku, Chiba 263-8522, Japan
Abstract
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 (ΔΨ; inside negative) by 3,3′-dihexyloxacarbocyanine iodide fluorescence revealed that the ΔΨ was hyperpolarized at pH 10 in JEM2; the ΔΨ 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. ΔΨ 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 ΔΨ (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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
23 articles.
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