Potassium/proton antiport system of Escherichia coli |
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Authors: | Radchenko Martha V Tanaka Kimihiro Waditee Rungaroon Oshimi Sawako Matsuzaki Yasutomo Fukuhara Masahiro Kobayashi Hiroshi Takabe Teruhiro Nakamura Tatsunosuke |
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Institution: | Department of Microbiology, Niigata University of Pharmacy and Applied Life Sciences, Niigata 950-2081, Japan. |
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Abstract: | 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. |
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