Potassium uptake with low affinity and high rate in Enterococcus hirae at alkaline pH.
Two high-affinity K+ uptake systems, KtrI and KtrII, have been reported in Enterococcus hirae. A mutant, JEMK1, defective in these two systems did not grow at pH 10 in low-K+ medium (less than 1 mM K+), but grew well when supplemented with 10 mM KCl. In this mutant, we found an energy-dependent K+ uptake at pH 10 with a low affinity for K+ (Km of approximately 20 mM) and an extremely high rate [Vmax of 1.6 micromol x min(-1) (mg protein)(-1)]. Rb+ uptake [Km of approximately 40 mM and Vmax of 0.5 micromol x min(-1) (mg protein)(-1)], which was inhibited competitively by K+ and less prominently by Cs+, was also observed. The specificity of this transport is likely to be K+>Rb+>Cs+. This peculiar K+ transport plays a role as a salvage mechanism against defects in high-affinity systems in the K+ homeostasis of this bacterium.
Faculty of Pharmaceutical Sciences, Chiba University, Japan.
M
M
Kawano
R
R
Abuki
K
K
Igarashi
Y
Y
Kakinuma
D000251:Adenosine Triphosphatases / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D001693:Biological Transport, Active; D002412:Cations / Q000378:metabolism; D002586:Cesium / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D016983:Enterococcus / Q000737:chemistry / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000235:genetics; D009154:Mutation; D011188:Potassium / Q000737:chemistry / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism / Q000494:pharmacology
D001426:Bacterial Proteins; D002412:Cations; D002712:Chlorides; D008565:Membrane Proteins; D002586:Cesium; D011189:Potassium Chloride; D000251:Adenosine Triphosphatases; C098928:NtpJ protein, bacteria; D012413:Rubidium; C032710:rubidium chloride; D011188:Potassium