Control of membrane potential by external H concentration in Bacillus subtilis as determined by an ion-selective electrode |
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Authors: | Shigeru Hosoi Noriko Mochizuki Shigeru Hayashi Michiki Kasai |
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Affiliation: | Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560 Japan |
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Abstract: | The membrane potential of intact bacteria was monitored by measuring the tetraphenylphosphonium ion distribution across the membrane using poly-(vinyl chloride) matrix-type electrode selective to tetraphenylphosphonium ion. It was found that the tetraphenylphosphonium ion was not countertransported against H+ movement. The membrane potential of Bacillus subtilis was estimated to be 80–120 mV inside-negative at external pH 7. The effect of the external pH on the membrane potential was studied. It varied from 30 to 40 mV/decade change in the external [H+] in the pH region of greater than 6.5, increasing pH making it more inside-negative. The addition of carbonyl cyanide m-chlorophenylhydrazone depolarized the membrane, and the membrane potential approached the H+ equilibrium potential. The addition of N,N′-dicyclohexylcarbodiimide did not abolish the pH dependence of the membrane potential. Increasing the external [K+] did not affect the pH dependence. CN− partially depolarized the membrane. A parallel conductance model for membrane potential could explain the results qualitatively. |
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Keywords: | Membrane potential External pH Electrogenic H+ pump H+-translocating ATPase Parallel conductance model Ion-selective electrode (Bacillus subtilis) |
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