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Brown GC, Brand MD. On the nature of the mitochondrial proton leak. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1059:55-62. [PMID: 1651764 DOI: 10.1016/s0005-2728(05)80187-2] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Respiring mitochondria have a significant passive permeability to protons; the mechanism of this proton leak is unknown. Several putative mechanisms were tested. Mitochondrial permeability to small sugars was unaffected by energization, suggesting that there is no significant dielectric breakdown at high membrane potential. Mitochondria are argued to have a proton permeability that is 6 to 8 orders of magnitude higher than the permeability to other cations, suggesting that the proton leak is probably not via a simple pore or membrane defect. 15-30% of the proton leak of freshly prepared mitochondria was extractable with bovine serum albumin and is probably due to fatty acids. Little if any of the proton leak appears to be due to cycling of ions other than protons, or to be associated with the functional activity of the proton pumps. The mitochondrial proton leak shares several properties with the proton permeability of pure phospholipid bilayers, suggesting that they share the same mechanism, although the leak through the bilayer in mitochondria may be modified by the presence of proteins.
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Affiliation(s)
- G C Brown
- Department of Biochemistry, University of Cambridge, U.K
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Turina MP, Venturoli G, Melandri BA. Evaluation of the buffer capacity and permeability constant for protons in chromatophores from Rhodobacter capsulatus. EUROPEAN JOURNAL OF BIOCHEMISTRY 1990; 192:39-47. [PMID: 2169415 DOI: 10.1111/j.1432-1033.1990.tb19192.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
1. The kinetics of decay in the dark of the transmembrane pH difference (delta pH) induced by light in nonphosphorylating chromatophores of Rhodobacter capsulatus were studied using the fluorescent probe 9-aminoacridine, in the presence of 50 mM KCl and 2 microM valinomycin. The transient fluorescence changes induced by acid to base transitions of chromatophore suspensions were used as an empirical calibration [Casadio, R. & Melandri, B. A. (1985) Arch. Biophys. Biochem. 238, 219-228]. The kinetic competence of the probe response was tested by accelerating the delta pH decay with the ionophore nigericin. 2. The time course in the dark of the increase in the internal pH in pre-illuminated chromatophores was analyzed on the basis of a model which assumes a certain number of internal buffers in equilibrium with the free protons and a diffusion-controlled H+ efflux [Whitmarsh, J. (1987) Photosynt. Res. 12, 43-62]. This model was extended to include the effects of the transmembrane electric potential difference on the H+ efflux. 3. The diffusion constant for proton efflux was measured at different values of the internal pH by evaluating the frequency of trains of single-turnover flashes capable of maintaining different delta pH in a steady state. The steady-state equation derived from the model does not include any parameter relative to the internal buffers and allows unequivocal determination of the diffusion constant on the basis of the known H+/e- ratio (equal to two) for the active proton translocation by the bacterial photosynthetic chain. A value for the first-order diffusion constant corresponding to a permeability coefficient, PH = 0.2 micron.s-1, was obtained at an external pH of 8.0; this value was constant for an internal pH ranging over 7.0-4.7. 4. Using the value of the diffusion constant determined experimentally, a satisfactory fitting of the kinetics of delta pH decay in the dark could be obtained when the presence of two internal buffers (with pK values of 3.6 and 6.7, respectively) was assumed. For these calculations, the time course of the transmembrane electric potential difference was evaluated from the electrochromic signal of carotenoids, calibrated with K(+)-induced diffusion potentials. The two internal buffers, suitable for modelling the behaviour of the system, were at concentrations of 250 mM (pK = 3.6) and 24 mM (pK = 6.7) respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- M P Turina
- Department of Biology, University of Bologna, Italy
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Zółkiewska A, Zabłocka B, Duszyński J, Wojtczak L. Resting state respiration of mitochondria: reappraisal of the role of passive ion fluxes. Arch Biochem Biophys 1989; 275:580-90. [PMID: 2556969 DOI: 10.1016/0003-9861(89)90404-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Rat liver mitochondria respiring under resting state conditions in the presence of oligomycin were rapidly blocked with cyanide and the dissipation of the membrane potential, measured with a tetraphenylphosphonium-sensitive electrode, was followed over time. The plot of the rate of membrane potential dissipation versus the actual value of the membrane potential was nonlinear and identical to the plot of resting state respiration (titrated with small amounts of a respiratory inhibitor) versus the membrane potential. The relationship between the respiratory chain activity and the proton-motive force in mitochondria oxidizing succinate with either oxygen or ferricyanide as electron acceptors was also found to be identical. These results are interpreted as an indication that the passive permeability of the inner mitochondrial membrane toward ions is far more significant in maintaining resting state respiration than is the molecular slippage of the pumps in the respiratory chain. These results also confirm the non-ohmic characteristics of the inner mitochondrial membrane.
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Affiliation(s)
- A Zółkiewska
- Department of Cellular Biochemistry, Nencki Institute of Experimental Biology, Warsaw, Poland
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Abstract
During oxidative phosphorylation by mammalian mitochondria part of the free energy stored in reduced substrates is dissipated and energy is released as heat. Here I review the mechanisms and the physiological significance of this phenomenon.
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Affiliation(s)
- M P Murphy
- Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY
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Kelly DJ, Richardson DJ, Ferguson SJ, Jackson JB. Isolation of transposon Tn5 insertion mutants of Rhodobacter capsulatus unable to reduce trimethylamine-N-oxide and dimethylsulphoxide. Arch Microbiol 1988. [DOI: 10.1007/bf00425153] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Murphy MP, Brand MD. Membrane-potential-dependent changes in the stoichiometry of charge translocation by the mitochondrial electron transport chain. EUROPEAN JOURNAL OF BIOCHEMISTRY 1988; 173:637-44. [PMID: 2836195 DOI: 10.1111/j.1432-1033.1988.tb14046.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The charge/oxygen (q+/O) stoichiometry of mitochondria respiring on succinate was measured under conditions of high membrane potential (delta psi). The technique used was a variation of the steady-state method of Al-Shawi and Brand [(1981) Biochem. J. 200, 539-546]. We show that q+/O was about 2.7 at high values of delta psi (170 mV). As delta psi was lowered from 170 mV to 85 mV with the respiratory inhibitor malonate the q+/O stoichiometry increased to 6.0. A number of artefacts which could have led to an underestimation of the q+/O stoichiometry were eliminated. These included effects of any rapid change in mitochondrial volume, internal pH, activity of the endogenous K+/H+ exchanger or in H+ conductance due to changes in delta psi after the addition of inhibitor. The experiments presented here are the first direct demonstration that the stoichiometry of proton pumping by the mitochondrial respiratory chain changes as delta psi is varied.
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Affiliation(s)
- M P Murphy
- Department of Biochemistry, University of Cambridge, England
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Ferguson SJ, Jackson J, McEwan AG. Anaerobic respiration in the Rhodospirillaceae: characterisation of pathways and evaluation of roles in redox balancing during photosynthesis. FEMS Microbiol Lett 1987. [DOI: 10.1111/j.1574-6968.1987.tb02455.x] [Citation(s) in RCA: 128] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Brand MD, Murphy MP. Control of electron flux through the respiratory chain in mitochondria and cells. Biol Rev Camb Philos Soc 1987; 62:141-93. [PMID: 3300795 DOI: 10.1111/j.1469-185x.1987.tb01265.x] [Citation(s) in RCA: 160] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Protonmotive activity of the cytochrome bc1 complex in chromatophores of Rhodobacter capsulatus in the presence of myxothiazol and antimycin A. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1987. [DOI: 10.1016/0005-2728(87)90026-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Brown GC, Brand MD. Changes in permeability to protons and other cations at high proton motive force in rat liver mitochondria. Biochem J 1986; 234:75-81. [PMID: 3010957 PMCID: PMC1146528 DOI: 10.1042/bj2340075] [Citation(s) in RCA: 92] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We have confirmed that the respiration rate of rat liver mitochondria can be substantially inhibited with only a small drop in proton motive force. We have directly measured the passive proton permeability as a function of delta psi by using K+ diffusion potentials and have shown that there is a large increase in proton permeability at high delta psi. This can quantitatively account for the inhibitor titrations of respiration. delta psi and delta pH were shown to have roughly equal effects on the relatively high respiration rate in static head. The permeabilities to K+, tetramethylammonium+ and choline+ were shown to increase greatly at high delta psi, in a similar way to proton permeability, indicating a similar mechanism of entry.
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Knaff DB. Active transport in phototrophic bacteria. PHOTOSYNTHESIS RESEARCH 1986; 10:507-514. [PMID: 24435399 DOI: 10.1007/bf00118317] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Phototrophic bacteria utilize light-driven, cyclic electron flow to pump protons out of their cytoplasm, creating an electrochemical proton gradient, ΔμH+, outside acid and positive. These bacteria exchange external protons for internal cations (Na(+), K(+) and Ca(+2)), allowing the cells to maintain a nearly constant internal pH while maintaining the electrical component of ΔμH+. Na(+)/H(+) exchange also establishes an electrochemical Na(+) gradient. Phototrophic bacteria are able to utilize these electrochemical gradients as energy sources for the uptake of a wide variety of metabolites (e.g., sugars, organic acids and amino acids) via metabolite/cation symports.
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Affiliation(s)
- D B Knaff
- Department of Chemistry and Biochemistry, Texas Tech University, 79409-4260, Lubbock, Texas, (U.S.A.)
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Jackson JB, Nicholls DG. Methods for the determination of membrane potential in bioenergetic systems. Methods Enzymol 1986; 127:557-77. [PMID: 3526088 DOI: 10.1016/0076-6879(86)27044-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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McEwan A, Cotton N, Ferguson S, Jackson J. The role of auxiliary oxidants in the maintenance of a balanced redox poise for photosynthesis in bacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1985. [DOI: 10.1016/0005-2728(85)90129-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Proton translocation in intact cells of the photosynthetic bacterium Rhodopseudomonas capsulata. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1985. [DOI: 10.1016/0005-2728(85)90136-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Seren S, Caporin G, Galiazzo F, Lippe G, Ferguson SJ, Sorgato MC. Current-voltage relationships for proton flow through the F0 sector of the ATP-synthase, carbonylcyanide-p-trifluoromethoxyphenylhydrazone or leak pathways in submitochondrial particles. EUROPEAN JOURNAL OF BIOCHEMISTRY 1985; 152:373-9. [PMID: 2865136 DOI: 10.1111/j.1432-1033.1985.tb09207.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Respiring submitochondrial particles from which the F1 sector of ATP-synthase was displaced generated a membrane potential in the range of 115-140 mV. Addition of oligomycin raised the membrane potential by approximately 40 mV. The lower membrane potential in particles with F1 displaced is attributed to partial dissipation of the proton electrochemical gradient as a consequence of proton flow through the open proton channels provided by the F0 sectors of the ATP-synthase. The characteristics of proton flow through the open F0 channels were studied by varying the rate of electron transport-driven proton translocation which permitted the establishment of a range of steady-state membrane potentials. Open F0 channels appeared to have a gated response to the membrane potential such that they were inoperative when the potential fell below approximately 110 mV. The membrane potential was measured as a function of respiratory rate in intact Mg-ATP submitochondrial particles that had been treated with low concentrations of the protonophore carbonylcyanide-p-trifluoromethoxyphenylhydrazone. In general a linear dependence of membrane potential upon respiratory rate was observed except at the lowest concentrations of protonophore and highest respiratory rates, presumably because the effect of the protonophore was then offset by an increased rate of proton translocation driven by the respiratory chain. The effect of increasing concentrations of carbonylcyanide-p-trifluoromethoxyphenylhydrazone on the membrane potential of respiring submitochondrial particles was studied. It was found that equal amounts of the protonophore lowered the membrane potential to a lesser extent at lower values of the membrane potential. Treatment of Mg-ATP submitochondrial particles with oligomycin slightly increased (by approximately 10 mV) the size of the respiration-dependent membrane potential, but did not alter the profile of membrane potential as a function of succinate oxidation rate. The latter was controlled by titration with malonate. This result indicates that the F0 sector of the ATP-synthase does not significantly contribute to leak pathways in intact submitochondrial particles.
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Bashford CL, Pasternak CA. Plasma membrane potential of neutrophils generated by the Na+ pump. BIOCHIMICA ET BIOPHYSICA ACTA 1985; 817:174-80. [PMID: 2408670 DOI: 10.1016/0005-2736(85)90080-x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The plasma membrane potential of human neutrophils was monitored using the anionic dye oxonol-V. The cells maintain a potential of -75 +/- 17 mV when suspended in physiological saline solutions. The cells are scarcely depolarized by extracellular K+ and the depolarization induced by the chemotactic peptide fMet-Leu-Phe is of similar magnitude for cells suspended in 5 or 155 mM K+. Neutrophils are, however, depolarized by suspension in K+-free media or after treatment with ouabain. Neutrophils catalyse Na+-H+ exchange and possess other electroneutral ion transport systems. We propose that the neutrophil membrane potential is generated by an electrogenic Na+ pump, that osmotic stability is achieved by electroneutral ion transport systems and that electrical stability is maintained by anion leakage. Similar mechanisms may also operate in other biological membranes.
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Patchett RA, Quilter JA, Jones CW. Energy conservation in whole cells of the methylotrophic bacterium Methylophilus methylotrophus. Arch Microbiol 1985. [DOI: 10.1007/bf00446747] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Control of the protonmotive force in Rhodopseudomonas sphaeroides in the light and dark and its effect on the initiation of flagellar rotation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1985. [DOI: 10.1016/0005-2728(85)90080-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Fenoll C, Gómez-Amores S, Ramírez JM. The membrane potential of intact Rhodospirillum rubrum cells in the absence of light-dependent and oxygen-linked electron transfer. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1985. [DOI: 10.1016/0005-2728(85)90093-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Hitchens GD, Kell DB. On the effects of thiocyanate and venturicidin on respiration-driven proton translocation in Paracoccus denitrificans. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 766:222-32. [PMID: 6743650 DOI: 10.1016/0005-2728(84)90235-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
A fast-responding O2 electrode has been used to confirm and extend observations of a significant kinetic discrepancy between O2 reduction and consequent proton translocation in 'O2-pulse' experiments in intact cells of P. denitrificans. The permeant, chaotropic SCN- ion abolishes this discrepancy, and greatly increases the observable----H+/O ratio, to a value approaching its accepted, true, limiting stoichiometry. The observable H+ decay rates are very slow, particularly in the absence of SCN-. The submaximal----H+/O ratios observed in the absence of SCN- are essentially independent of the size of the O2 pulse, in a manner not easily explained by a delocalised chemiosmotic energy-coupling scheme. Osmotically active protoplasts of P. denitrificans do not show a significant kinetic discrepancy between O2 reduction and H+ translocation, even in the the absence of SCN-. However, the submaximal----H+/O ratios observed in the absence of SCN- are again essentially independent of the size of the O2 pulse. As in intact cells, the observable H+ decay rates are very slow. The energy-transfer inhibitor venturicidin causes a significant increase in the----H+/O ratio observed in protoplasts of P. denitrificans in the absence of SCN-; the decay kinetics of the H+ translocation process are also somewhat modified. Nevertheless, the----H+/O ratio observed in the presence of venturicidin is also independent of the size of the O2 pulse. This observation militates further against arguments in which (a) a non-ohmic leak of protons from the bulk aqueous phase might alone be the cause of the low----H+/O ratios observed in the absence of SCN-, and (b) in which there might be a delta p-dependent change ('redox slip') in the actual----H+/O ratio. It is concluded that the observable protonmotive activity of the respiratory chain of P. denitrificans in the absence of SCN- is directly influenced by the state of the H+-ATP synthetase in the cytoplasmic membrane of this organism. We are unable to explain the data in terms of a model in which the putative protonmotive force may be acting to affect the----H+/O ratio. The possibility is considered that the delocalised bulk-to-bulk phase membrane potential set up in response to protonmotive activity is energetically insignificant.
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Cotton NP, Clark AJ, Jackson JB. Changes in membrane ionic conductance, but not changes in slip, can account for the non-linear dependence of the electrochemical proton gradient upon the electron-transport rate in chromatophores. EUROPEAN JOURNAL OF BIOCHEMISTRY 1984; 142:193-8. [PMID: 6745265 DOI: 10.1111/j.1432-1033.1984.tb08269.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Decrease in the rate of cyclic electron transport (JE) measured from the absorbance changes associated with reaction centre bacteriochlorophyll led to a less than proportionate decrease in the membrane potential (delta psi) measured by electrochromism. In principle this result can be explained either by a delta psi-dependent slip in the H+/e- coupling ratio (nE) or by a delta psi-dependent change in the membrane ionic conductance. Simultaneous measurement of the membrane ionic current (JDIS) did not reveal any significant changes in the H+/e- ratio (JDIS/JE) and showed that conductance changes (JDIS/delta psi) account quantitatively for the curved dependence of delta psi on JE. Simultaneous recordings of JDIS and the extravesicular pH from cresol-red absorbance changes, suggest that protons are the main current-carrying species across the chromatophore membrane at high values of delta psi in the presence and absence of Fo-ATPase inhibitor. At reduced delta psi the flux of other ions outweighs the hydrogen ion current.
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McEwan AG, Jackson JB, Ferguson SJ. Rationalization of properties of nitrate reductases in Rhodopseudomonas capsulata. Arch Microbiol 1984. [DOI: 10.1007/bf00410732] [Citation(s) in RCA: 67] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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McEwan AG, Ferguson SJ, Jackson JB. Electron flow to dimethylsulphoxide or trimethylamine-N-oxide generates a membrane potential in Rhodopseudomonas capsulata. Arch Microbiol 1983; 136:300-5. [PMID: 6667089 DOI: 10.1007/bf00425221] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Under dark and essentially anaerobic conditions electron flow to either dimethylsulphoxide or trimethylamine-N-oxide in cells of Rhodopseudomonas capsulata has been shown to generate a membrane potential. This conclusion is based on the observation of a red shift in the carotenoid absorption band which is a well characterised indicator of membrane potential in this bacterium. The magnitude of the dimethylsulphoxide- or trimethylamine-N-oxide-dependent membrane potential was reduced either by a protonophore uncoupler of oxidative phosphorylation or synergistically by a combination of a protonophore plus rotenone, an inhibitor of electron flow from NADH dehydrogenase. These findings, together with the observation that venturicidin, an inhibitor of the proton translocating ATPase, did not reduce the membrane potential, show that electron flow to dimethylsulphoxide or trimethylamine-N-oxide is coupled to proton translocation. Thus contrary to some previous proposals dark and anaerobic growth of Rps. capsulata in the presence of dimethylsulphoxide or trimethylamine-N-oxide cannot be regarded as purely fermentative.
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Clark A, Cotton N, Jackson J. The relation between membrane ionic current and ATP synthesis in chromatophores from Rhodopseudomonas capsulata. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1983. [DOI: 10.1016/0005-2728(83)90051-8] [Citation(s) in RCA: 70] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Cotton NP, Clark AJ, Jackson JB. Interaction between the respiratory and photosynthetic electron transport chains of intact cells of Rhodopseudomonas capsulata mediated by membrane potential. EUROPEAN JOURNAL OF BIOCHEMISTRY 1983; 130:581-7. [PMID: 6825711 DOI: 10.1111/j.1432-1033.1983.tb07189.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
1. The inhibition of respiration by light and the relief from this inhibition by uncoupling agents have been studied in intact cells of Rhodopseudomonas capsulata. 2. The same concentration range of carbonylcyanide p-trifluoromethoxyphenylhydrazone [CF3OPhzC(CN)2] prevented light-inhibition of respiration and depressed the membrane potential (delta psi) in illuminated, aerobic bacterial suspensions. 3. For a wide range of CF3OPhzC(CN)2 concentration the dependence of the respiration rate on delta psi in darkened cells coincided with that in illuminated cells. 4. When present separately, antimycin A and low concentrations of CF3OPhzC(CN)2 had little effect on light-inhibition of respiration or on delta psi in illuminated, aerobic cells, but added together they gave relief from light-inhibition and they lowered delta psi. 5. In the absence of CF3OPhzC(CN)2 even very low light intensities were sufficient to inhibit respiration and increase delta psi. In the presence of CF3OPhzC(CN)2 much higher light intensities were necessary. 6. The results are interpreted as evidence that light-inhibition of respiration is mediated by delta psi. The modification of the response by uncouplers, inhibitors and with light intensity is critically determined by the ionic conductance properties of the membrane in accordance with the findings in [Clark, A.J., Cotton, N.P.J., and Jackson, J.B. (1983) Eur. J. Biochem. 130, 575-580].
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