Monitoring of the Membrane Potentials in E. coli and in Mitochondria by use of a Selective-Electrode for Tetraphenyl Phosphonium Ion (TPP+)

Muratsugu M., Kamo N., Kobatake Y., Suda Y.

doi:10.5360/membrane.4.323

The membrane potential of E. coli and mitochondria were determined by tetraphenyl phosphonium (TPP⁺) distribution. The change of TPP⁺ concentration in medium was meassred with a TPP⁺-selective electrode. (1) A polyvinyl chloride (PVC)-based membrane electrode sensitive to TPP⁺ was constructed. Rapid and the Nernstian responses were obtained for TPP solutions ranging between 10^-2 and 10^-6 M in concentration. High selectivity for TPP was observed in the presence of various inorganic salts, nucleotides, oxidizable substrates and sugars. (2) Analysis of the time-course of TPP uptake confirmed the notion that TPP diffused electrophoretically across biological membranes. (3) After correction of the bound TPP on E. coli cell surface, the membrane potential, Δφ, was evaluated. Δφ of E. coli cells was changed in accordance with pH in the medium so that the proton motive force stayed constant at -178mV. (4) The binding of TPP on mitochondrial membrane surface was negligibly small for calculation of the membrane potential, Δφ. Δφ of mitochondria was-150 to -180mV for energized condition and about -100mV for de-energized condition. (5) Δφ of mitochondria at the state 3 was smaller than that at the state 4. In the state 4, the relationship between phosphorylation potential, ΔG_p, and Δφ was obtained as follows: ΔG_p=3FΔφ

Monitoring of the Membrane Potentials in E. coli and in Mitochondria by use of a Selective-Electrode for Tetraphenyl Phosphonium Ion (TPP<SUP>+</SUP>)

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