Potassium uptake with low affinity and high rate in Enterococcus hirae at alkaline Ph

Kawano, M Abuki, R Igarashi, K Kakinuma, Y

M. Kawano et al., Potassium uptake with low affinity and high rate in Enterococcus hirae at alkaline Ph, ARCH MICROB, 175(1), 2001, pp. 41-45

24

INGLESE

Article

Microbiology

ARCHIVES OF MICROBIOLOGY

0302-8933 → ACNP

175

1

2001

41 - 45

ISI

0302-8933(200101)175:1<41:PUWLAA>2.0.ZU;2-Z

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 sup plemented with 10 mM KCl. In this mutant. we found an energy-dependent K+ u ptake at pH 10 with a low affinity for K+ (K-m of similar to 20 mM) and an extremely high rate [V-max of 1.6 mu mol min(-1) (mg protein)(-1)]. Rb+ upt ake [K-m of similar to 40 mM and V-max of 0.5 mu mol min(-1) (mg protein)(- 1), which was inhibited competitively by Ki and less prominently by Cs+, wa s also observed. The specificity of this transport is likely to be K+>Rb+>C s+. This peculiar K+ transport plays a role as a salvage mechanism against defects in high-affinity systems in the K+ homeostasis of this bacterium.