SUMMARY: The lipophilic cations butyltriphenylphosphonium (BTPP), tetraphenylphosphonium (TPP) and triphenylmethylphosphonium (TPMP) were taken up into cells of H18 under anaerobic conditions. Uptake was dependent on the presence of maltose together with both HCO and Na; it was at a maximum at concentrations of ≥ 20 mM-HCO and ≤ 2 mM-Na. The addition of 2-(n-heptyl)-hydroxyquinoline--oxide (HpHOQnO) or of an uncoupler of oxidative phosphorylation, or air, resulted in efflux of the lipophilic cations. From the binding behaviour and the physiological effects of the lipophilic cations, a membrane potential (δ ψ) of 140 mV was estimated. There was no detectable δpH at an external pH of 6.7. The cytoplasmic Naconcentration was estimated to be 0.2 mM, indicating that can maintain a Naconcentration gradient equivalent to at least 150 mV. Variation in the external Naconcentration (2 to 180 mM) had little influence on δ ψ. High external concentrations of the fermentation products acetate, formate and succinate had little effect on the growth rate and the δ ψ. The cytoplasmic ATP concentration decreased rapidly on addition of HpHOQnO oxide or of an uncoupler. The maximum internal ATP concentration was only maintained at an external concentration≥2mM-Na. The NADH: fumarate reductase activity of vesicles of was associated with alkalization of the suspension medium. The amount of Htaken up was in excess of the expected amount of scalar Hand was partially sensitive to uncoupler. It is concluded that the δ ψ was generated via Htranslocation driven primarily by the cytochrome-deficient NADH: fumarate reductase system. The transmembrane Nagradient could be supported via the action of a Na/2 Hantiporter.


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