Potassium/proton antiport system of Escherichia coli.
The intracellular level of potassium (K(+)) in Escherichia coli is regulated through multiple K(+) transport systems. Recent data indicate that not all K(+) extrusion system(s) have been identified (15). Here we report that the E. coli Na(+) (Ca(2+))/H(+) antiporter ChaA functions as a K(+) extrusion system. Cells expressing ChaA mediated K(+) efflux against a K(+) concentration gradient. E. coli strains lacking the chaA gene were unable to extrude K(+) under conditions in which wild-type cells extruded K(+). The K(+)/H(+) antiporter activity of ChaA was detected by using inverted membrane vesicles produced using a French press. Physiological growth studies indicated that E. coli uses ChaA to discard excessive K(+), which is toxic for these cells. These results suggest that ChaA K(+)/H(+) antiporter activity enables E. coli to adapt to K(+) salinity stress and to maintain K(+) homeostasis.
Radchenko
Martha V
MV
Department of Microbiology, Niigata University of Pharmacy and Applied Life Sciences, Niigata 950-2081, Japan.
Tanaka
Kimihiro
K
Waditee
Rungaroon
R
Oshimi
Sawako
S
Matsuzaki
Yasutomo
Y
Fukuhara
Masahiro
M
Kobayashi
Hiroshi
H
Takabe
Teruhiro
T
Nakamura
Tatsunosuke
T