The effect of venturicidin on light and oxygen-dependent electron transport, proton translocation, membrane potential development and ATP synthesis in intact cells of Rhodopseudomonas capsulata

1. The membrane potential in intact cells of Rhodopseudomonas capsulata during photosynthesis and during dark respiration has been measured by two independent methods. 2. The light-induced and O2-induced shifts in the carotenoid absorption spectrum were measured in the intact cells. The shift was calibrated with K+-diffusion potentials in chromatophores derived from those cells. The light-induced and O2-induced membrane potentials were -290 mV and -230 mV respectively. 3. The energized uptake of butyltriphenylphosphonium ions was measured in the same batch of cells. The light-induced and O2-induced membrane potentials calculated from the Nernst equation were -160 mV and -120 mV respectively. 4. It is concluded that the two kinds of probe measure the electric potentials across different domains of the cytoplasmic membrane, but it is difficult to reconcile the existence of such domains with simple electrical analogues of the membrane and aqueous phases.

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Recording and Simulating Proton-Related Metabolism in Bacterial Cell Suspensions

Frontiers in Microbiology ◽

10.3389/fmicb.2021.654065 ◽

2021 ◽

Vol 12 ◽

Author(s):

Heribert Cypionka ◽

Jan-Ole Reese

Keyword(s):

Membrane Potential ◽

Electron Transport ◽

Proton Translocation ◽

Model Organism ◽

Desulfovibrio Desulfuricans ◽

Cell Suspensions ◽

Nitrite Reduction ◽

Turnover Rates ◽

Metabolic Activities ◽

Nitrate And Nitrite

Proton release and uptake induced by metabolic activities were measured in non-buffered cell suspensions by means of a pH electrode. Recorded data were used for simulating substrate turnover rates by means of a new freeware app (proton.exe). The program applies Michaelis-Menten or first-order kinetics to the metabolic processes and allows for parametrization of simultaneously ongoing processes. The simulation includes changes of the transmembrane ΔpH, membrane potential and ATP gains, and demonstrates the principles of chemiosmotic energy conservation. In our experiments, the versatile sulfate-reducing bacterium Desulfovibrio desulfuricans CSN (DSM 9104) was used as model organism. We analysed sulfate uptake by proton-sulfate symport, scalar alkalinization by sulfate reduction to sulfide, as well as nitrate and nitrite reduction to ammonia, and electron transport-coupled proton translocation. Two types of experiments were performed: In oxidant pulse experiments, cells were kept under H2, and micromolar amounts of sulfate, nitrate or nitrite were added. For reductant pulse experiments, small amounts of H2-saturated KCl were added to cells incubated under N2 with an excess of one of the above-mentioned electron acceptors. To study electron-transport driven proton translocation, the membrane potential was neutralized by addition of KSCN (100 mM). H+/e– ratios of electron-transport driven proton translocation were calculated by simulation with proton.exe. This method gave lower but more realistic values than logarithmic extrapolation. We could verify the kinetic simulation parameters found with proton.exe using series of increasing additions of the reactants. Our approach allows for studying a broad variety of proton-related metabolic activities at micromolar concentrations and time scales of seconds to minutes.

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The Influence of the Ionic Conductance on the Relation between Electron Transport and Proton-Motive Force in Intact Cells of Rhodopseudomonas capsulata

European Journal of Biochemistry ◽

10.1111/j.1432-1033.1983.tb07188.x ◽

1983 ◽

Vol 130 (3) ◽

pp. 575-580 ◽

Cited By ~ 30

Author(s):

Adam J. CLARK ◽

Nicholas P. J. COTTON ◽

J. Barry JACKSON

Keyword(s):

Electron Transport ◽

Proton Motive Force ◽

Motive Force ◽

Rhodopseudomonas Capsulata ◽

Ionic Conductance ◽

Intact Cells

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Redox regulation of mitochondrial functional activity by quinones

Physiology International ◽

10.1556/2060.103.2016.4.4 ◽

2016 ◽

Vol 103 (4) ◽

pp. 439-458 ◽

Cited By ~ 4

Author(s):

NG Krylova ◽

TA Kulahava ◽

VT Cheschevik ◽

IK Dremza ◽

GN Semenkova ◽

...

Keyword(s):

Membrane Potential ◽

Electron Transport ◽

Mitochondrial Membrane Potential ◽

Mitochondrial Function ◽

Mitochondrial Membrane ◽

Reduction Potential ◽

Electron Flow ◽

Rat Liver Mitochondria ◽

Ros Generation ◽

Intact Cells

Quinones are among the rare compounds successfully used as therapeutic agents to correct mitochondrial diseases and as specific regulators of mitochondrial function within cells. The aim of the present study was to elucidate the redox-dependent effects of quinones on mitochondrial function. The functional parameters [respiratory activity, membrane potential, and reactive oxygen species (ROS) generation] of isolated rat liver mitochondria and mitochondria in intact cells were measured in the presence of eight exogenously applied quinones that differ in lipophilicity and one-electron reduction potential. The quinones affected the respiratory parameters of mitochondria, and dissipated the mitochondrial membrane potential as well as influenced (either decreased or enhanced) ROS generation, and restored the electron flow during electron transport chain inhibition. The stimulation of ROS production by juglone and 2,5-di-tert-butyl-1,4-benzoquinone was accompanied by a decrease in the acceptor control and respiration control ratios, dissipation of the mitochondrial membrane potential and induction of the reverse electron flow under succinate oxidation in isolated mitochondria. Menadione and 2,3,5-trimethyl-1,4-benzoquinone, which decreased the mitochondrial ROS generation, did not affect the mitochondrial potential and, vice versa, were capable of restoring electron transport during Complex I inhibition. In intact C6 cells, all the quinones, except for coenzyme Q10, decreased the mitochondrial membrane potential. Juglone, 1,4-benzoquinone, and menadione showed the most pronounced effects. These findings indicate that quinones with the reduction potential values E1/2 in the range from −99 to −260 mV were effective redox regulators of mitochondrial electron transport.

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Effect of growth conditions on the involvement of cytochrome c in electron transport, proton translocation and ATP synthesis in the facultative methylotroph Pseudomonas AM1

Biochemical Journal ◽

10.1042/bj1820071 ◽

1979 ◽

Vol 182 (1) ◽

pp. 71-79 ◽

Cited By ~ 9

Author(s):

C. William Keevil ◽

Christopher Anthony

Keyword(s):

Electron Transport ◽

Cytochrome C ◽

Proton Translocation ◽

Atp Synthesis ◽

Growth Conditions ◽

Wild Type ◽

Limited Growth ◽

Bacterial Membranes ◽

Facultative Methylotroph ◽

Carbon Excess

The stoicheiometry of proton translocation, the amounts of cytochromes firmly bound to membranes, and cell yields with respect to succinate and O2 have been measured in the facultative methylotroph Pseudomonas AM1 and in the mutant lacking cytochrome c (mutant PCT76) during carbon-limited growth and carbon-excess growth. →H+/O ratios during endogenous respiration of about 4 were measured in wild-type bacteria grown in carbon-excess conditions, and in the mutant in all growth conditions. During methanol- or succinate-limited growth of wild-type bacteria the →H+/O ratio increased to about 6. Cell yields with respect to succinate and O2 were higher in wild-type than in the mutant lacking cytochrome c by an amount suggesting loss in the mutant of 30% of the ATP-generating capacity of wild-type bacteria. During carbon-limited growth on methanol or succinate some cytochrome c was tightly bound to bacterial membranes, whereas none was tightly bound in bacteria grown in batch-culture or in NH4+-limited conditions. It is proposed that the role of cytochrome c in Pseudomonas AM1 depends on growth conditions and hence on the ‘needs’ of the bacteria. During growth in carbon-excess conditions it is only required for methanol oxidation, mediating between methanol dehydrogenase and cytochrome a/a3. In these conditions oxidation of NADH and succinate by way of cytochrome b and cytochrome a/a3 occurs without the mediation of cytochrome c. This is the only route for oxidation of NADH and succinate in the cytochrome c-deficient mutant in all growth conditions. During carbon-limited growth the cytochrome c becomes bound to the membrane in such a way that it can mediate between cytochromes b and a/a3, hence becoming involved in proton translocation and ATP synthesis during NADH and succinate oxidation. An alternative possibility is that in wild-type bacteria the cytochrome c is always involved in electron transport, but that its involvement in measurable proton translocation only occurs in carbon-limited conditions.

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