Measurement and significance of the membrane potential in Methanoba cterium bryantii |
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Authors: | Ken F. Jarrell G.Dennis Sprott |
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Affiliation: | Division of Biological Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6 Canada |
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Abstract: | The membrane potential (Δψ) of Methanobacterium bryantii was 133–142 mV as measured from the distribution of 86Rb+ in valinomycin-treated cells, and was considerably higher than that obtained using triphenylmethylphosphonium in the presence of tetraphenylboron. The Δψ measured using the Rb+/valinomycin method was sensitive to certain ionophores including gramicidin, nigericin, carbonyl cyanide m-chlorophenylhydrazone and 3,3′,4′,5-tetrachlorosalicylanilide. It was also dissipated by 1 mM tetraphenylphosphonium and was abolished in heat-treated or permeabilized cells. The Δψ could be varied by adjusting the extracellular potassium concentration in valinomycin-treated cells. Monensin-treated cells possessed a significantly increased Δψ, as monitored by the Rb+ / valinomycin method. Tetraphenylphosphonium cation (1 mM) abolished methane synthesis, intracellular ATP and Δψ, supporting a role for Δψ in ATP and CH4 synthesis. However, lower concentrations of the lipophilic cation (50 μM) greatly elevated both the intracellular ATP concentration and Δψ but decreased the rate of CH4 synthesis by almost 50%. Thus, tetraphenylphosphonium cation exerts a primary inhibitory effect on CH4 synthesis which cannot be attributed to the loss of Δψ or ATP. |
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Keywords: | Membrane potential Methanogenesis (Methanobacterium bryantii) CCCP TPB tetraphenylboron TPMP triphenylmethylphosphonium TCS 3,3′,4′,5-tetrachlorosalicylanilide TPP tetraphenylphosphonium Hepes |
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