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Evron Y, Johnson EA, McCarty RE. Regulation of proton flow and ATP synthesis in chloroplasts. J Bioenerg Biomembr 2009; 32:501-6. [PMID: 15254385 DOI: 10.1023/a:1005669008974] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The chloroplast ATP synthase is strictly regulated so that it is very active in the light (rates of ATP synthesis can be higher than 5 micromol/min/mg protein), but virtually inactive in the dark. The subunits of the catalytic portion of the ATP synthase involved in activation, as well as the effects of nucleotides are discussed. The relation of activation to proton flux through the ATP synthase and to changes in the structure of enzyme induced by the proton electrochemical gradient are also presented. It is concluded that the gamma and epsilon subunits of CF(1) play key roles in both regulation of activity and proton translocation.
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Affiliation(s)
- Y Evron
- Department of Biology, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA
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Gould J. The relationship between proton fluxes and the regulation of electron transport in chloroplasts. FEBS Lett 2001. [DOI: 10.1016/0014-5793(76)80529-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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5
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Evron Y, McCarty RE. Simultaneous measurement of deltapH and electron transport in chloroplast thylakoids by 9-aminoacridine fluorescence. PLANT PHYSIOLOGY 2000; 124:407-14. [PMID: 10982453 PMCID: PMC59153 DOI: 10.1104/pp.124.1.407] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2000] [Accepted: 05/29/2000] [Indexed: 05/22/2023]
Abstract
Electron transport and the electrochemical proton gradient across the thylakoid membrane are two fundamental parameters of photosynthesis. A combination of the electron acceptor, ferricyanide and the DeltapH indicator, 9-aminoacridine, was used to measure simultaneously electron transport rates and DeltapH solely by changes in the fluorescence of 9-aminoacridine. This method yields values for the rate of electron transport that are comparable with those obtained by established methods. Using this method a relationship between the rate of electron transport and DeltapH at various uncoupler concentrations or light intensities was obtained. In addition, the method was used to study the effect of reducing the disulfide bridge in the gamma-subunit of the chloroplast ATP synthase on the relation of electron transport to DeltapH. When the ATP synthase is reduced and alkylated, the threshold DeltapH at which the ATP synthase becomes leaky to protons is lower compared with the oxidized enzyme. Proton flow through the enzyme at a lower DeltapH may be a key step in initiation of ATP synthesis in the reduced enzyme and may be the way by which reduction of the disulfide bridge in the gamma-subunit enables high rates of ATP synthesis at low DeltapH values.
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Affiliation(s)
- Y Evron
- Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA
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6
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Apostolova EL, Ivanov AG. Effects of monofunctional sulfhydryl reagents on the proton permeability of pea thylakoid membranes. J Electroanal Chem (Lausanne) 1991. [DOI: 10.1016/0022-0728(91)85569-b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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7
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Evron Y, Avron M. Characterization of an alkaline pH-dependent proton ‘slip’ in the ATP synthase of lettuce thylakoids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1990. [DOI: 10.1016/0005-2728(90)90131-m] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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8
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Hopkins WG. Effect of low growth temperature on coupling between electron transport and proton flux in Vicia faba thylakoids. PHYSIOLOGIA PLANTARUM 1990; 79:649-655. [PMID: 21087274 DOI: 10.1111/j.1399-3054.1990.tb00039.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Coupling between electron transport and proton flux has been compared in chloroplasts from Vicia faba (cv. Windsor) plants grown at 20 and 5°C. Proton uptake by warm-grown thylakoids was sensitive to external pH and stimulated by micromolar adenine nucleotide above pH 7.0. Electron transport was modulated by pH, adenine nucleotide and energy transfer inhibitors (triphenyltin and Hg(2+) ). By contrast, proton uptake by cold-grown thylakoids was generally lower and was insensitive to micromolar ATP. The rate of non-phosphorylating electron flow in cold-grown thylakoids was relatively insensitive to pH and Hg(2+) and was not modulated by adenine nucleotides or triphenyltin. Stimulation of electron transport by phosphorylating conditions in cold-grown thylakoids was generally lower and insensitive to pH. It is concluded that the control of proton efflux through CF(0) -CF(1) differs in thylakoids of V. faba grown at warm and cold temperatures.
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Affiliation(s)
- W G Hopkins
- Dept of Plant Sciences, Univ. of Western Ontario, London, Ontario, Canada N6A 5B7
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9
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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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Double inhibitor titrations of photophosphorylation are consistent with delocalized coupling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1985. [DOI: 10.1016/0005-2728(85)90262-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Davenport JW, McCarty RE. An analysis of proton fluxes coupled to electron transport and ATP synthesis in chloroplast thylakoids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1984. [DOI: 10.1016/0005-2728(84)90252-4] [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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12
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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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Pietrobon D, Zoratti M, Azzone GF. Molecular slipping in redox and ATPase H+ pumps. BIOCHIMICA ET BIOPHYSICA ACTA 1983; 723:317-21. [PMID: 6221758 DOI: 10.1016/0005-2728(83)90131-7] [Citation(s) in RCA: 109] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The titration of the mitochondrial ATPase H+ pump with oligomycin has been compared with the titration of the redox H+ pump with antimycin. In both cases there is extensive inhibition of the pumps without significant depression of delta muH. The two pumps exhibit 'nonohmic' behavior in different ranges of delta muH. This discrepancy favors the hypothesis of nontightly coupled or 'slipping' H+ pumps with respect to that of a steep dependence of the membrane 'leak' conductance for H+ on delta muH.
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14
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Graan T, Ort DR. Initial events in the regulation of electron transfer in chloroplasts. The role of the membrane potential. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32792-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Moroney JV, Warncke K, McCarty RE. The distance between thiol groups in the gamma subunit of coupling factor 1 influences the proton permeability of thylakoid membranes. J Bioenerg Biomembr 1982; 14:347-59. [PMID: 6298195 DOI: 10.1007/bf00743063] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Spinach chloroplast thylakoids treated in the light with bifunctional maleimides were previously shown to be uncoupled. The increase in proton permeability by these reagents is caused by the cross-linking of an accessible group on the gamma subunit of coupling factor 1 (CF1) to a group that becomes exposed to reaction with maleimides only when the thylakoids are energized. In this study, several bifunctional maleimides, including o-, m-, and p-phenylenebismaleimides, 2,3- and 1,5-naphthalenebismaleimides, and azophenylbismaleimide, were tested for their ability to form cross-links and to uncouple photophosphorylation. These reagents form cross-links from about 6 to 19 A. Each reagent was found to form cross-links in the light and to inhibit photophosphorylation. However, the effectiveness of these compounds as uncouplers decreased as the distance between the cross-linked groups increased, indicating that the distance between two groups on the gamma subunit of CF1 can regulate proton flux through the membrane. Monofunctional maleimides cause a light-dependent energy transfer type of inhibition of photophosphorylation. Although this inhibition was correlated to the reaction of the maleimide with a group on the gamma subunit that is exposed only in energized thylakoids, the accessible group on this subunit was also modified by the reagent. However, we show here that the accessible group plays no role in the inhibition of photophosphorylation. This group may be blocked by incubating thylakoids in the dark with methyl methanethiolsulfonate. The light-dependent inhibition of photophosphorylation by N-ethylmaleimide was unaffected by this treatment or by the subsequent removal of the methanethiol moiety from the accessible group.
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Guerrieri F, Papa S. Effect of thiol reagents on the proton conductivity of the H+-ATPase of mitochondria. EUROPEAN JOURNAL OF BIOCHEMISTRY 1982; 128:9-13. [PMID: 6293829 DOI: 10.1111/j.1432-1033.1982.tb06923.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The role of thiol groups in the proton conduction by the H+-ATPase of mitochondria is examined. A detailed kinetic analysis of the effect of arsenite and N-ethylmaleimide on the anaerobic relaxation of the proton gradient set up by respiration in 'inside-out' submitochondrial particles from beef-heart has been carried out. Arsenite, which reacts with vicinal dithiols, is shown to enhance the proton conductivity of the H+-ATPase. This effect is exerted on the F0 moiety of the complex and apparently mimics and is, in fact, favoured by a state of high proton conductivity induced in the complex by the respiratory delta mu H+. N-Ethylmaleimide (MalNEt), which is a permeant monothiol blocking reagent, appears to attack critical -SH groups in a reaction leading to inhibition of the proton conductivity of the H+-ATPase. Also the inhibitory action of MalNEt on proton conduction is exerted on the F0 moiety of the H+-ATPase. Whilst the stimulatory effect of arsenite develops rapidly, the inhibitory action of MalNEt is sluggish and takes more than 10 min to fully develop. This and other kinetic characteristics, as well a partial additivity of the inhibition by MalNEt with that by oligomycin, indicate that the inhibitory action of MalNEt is associated to a substantial conformational transition in F0. Differences in the mechanism of inhibition of proton conduction by MalNEt and triphenyltin are also presented.
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Guerrieri F, Papa S. Effect of chemical modifiers of amino acid residues on proton conduction by the H+-ATPase of mitochondria. J Bioenerg Biomembr 1981; 13:393-409. [PMID: 6460757 DOI: 10.1007/bf00743212] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The effect of chemical modifiers of amino acid residues on the proton conductivity of H+-ATPase in "inside out" submitochondrial particles has been studied. Treatment of submitochondrial particles prepared in the presence of EDTA (ESMP) with the arginine modifiers, phenylglyoxal or butanedione, or the tyrosine modifier, tetranitromethane, caused inhibition of the ATPase activity. Phenylglyoxal and tetranitromethane also caused inhibition of the anaerobic release of respiratory delta micro H+ in ESMP as well as in particles deprived of F1 (USMP). Butanedione treatment caused, on the contrary, acceleration of anaerobic proton release in both particles. The inhibition of proton release caused by phenylglyoxal and tetranitromethane exhibition in USMP a sigmoidal titration curve. The same inhibitory pattern was observed with oligomycin and with N,N'-dicyclohexylcarbodiimide. In ESMP, relaxation of delta micro H+ exhibited two first-order phases, both an expression of the H+ conductivity of the ATPase complex. The rapid phase results from transient enhancement of H+ conduction caused by respiratory delta micro H+ itself. Oligomycin, N,N'-dicyclohexylcarbodiimide, and tetranitromethane inhibited both phases of H+ release, and butanedione accelerated both. Phenylglyoxal inhibited principally the slow phase of H+ conduction. In USMP, H+ release followed simple first-order kinetics. Oligomycin depressed H+ release, enhanced respiratory delta micro H+, and restored the biphasicity of H+ release. Phenylglyoxal and tetranitromethane inhibited H+ release in USMP without modifying its first-order kinetics. Butanedione treatment caused biphasicity of H+ release from USMP, introducing a very rapid phase of H+ release. Addition of soluble F1 to USMP also restored biphasicity of H+ release. A mechanism of proton conduction by Fo is discussed based on involvement of tyrosine or other hydroxyl residues, in series with the DCCD-reactive acid residue. There are apparently two functionally different species of arginine or other basic residues: those modified by phenylglyoxal, which facilitate H+ conduction, and those modified by butanedione, which retard H+ diffusion.
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19
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Quantitative aspects of adenosine triphosphate-driven proton translocation in spinach chloroplast thylakoids. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)52491-7] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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20
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Underwood C, Gould JM. Modulation of proton efflux from chloroplasts in the light by external pH. Arch Biochem Biophys 1980; 204:241-6. [PMID: 7425639 DOI: 10.1016/0003-9861(80)90029-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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21
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Moroney J, Andreo C, Vallejos R, McCarty R. Uncoupling and energy transfer inhibition of photophosphorylation by sulfhydryl reagents. J Biol Chem 1980. [DOI: 10.1016/s0021-9258(18)43622-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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[66] Delineation of the mechanism of ATP synthesis in chloroplasts: Use of uncouplers, energy transfer inhibitors, and modifiers of coupling factor 1. Methods Enzymol 1980. [DOI: 10.1016/s0076-6879(80)69068-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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23
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24
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Ho YK, Liu CJ, Saunders DR, Wang JH. Light dependence of the decay of the proton gradient in broken chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 547:149-60. [PMID: 37901 DOI: 10.1016/0005-2728(79)90103-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The initial rates and steady-state values of proton uptake by broken chloroplasts have been measured as functions of light intensity at various concentrations of chlorophyll, pyocyanine, supporting electrolyte, buffer, as well as pH and temperature. Kinetics analysis of the data shows that the rate of decay of proton gradient due to backward leakage depends on light intensity. Under steady illumination, the decay constant kL is equal to kD + mR0, where R0 is the initial rate of proton uptake which is a function of light intensity, kD is the decay constant in the dark and m is a parameter which is independent of light intensity. Treatment of chloroplasts with lysolecithin, neutral detergent, 2,4-dinitrophenol, or valinomycin in the presence of K+ increases kD without affecting m. Treatment with N,N'-dicyclohexylcarbodiimide or adenylyl imidodiphosphate under appropriate conditions decreases m without affectsity and hence m = 0. These results suggest that the light-dependent part (mR0) of kL is due to leakage of protons through the coupling factor (CF1-CF0) complex which can open or close depending on light intensity and that the light independent part (kD) of the decay constant kL is due to proton leakage elsewhere.
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25
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Pansini A, Guerrieri F, Papa S. Control of proton conduction by the H+ -ATPase in the inner mitochondrial membrane. EUROPEAN JOURNAL OF BIOCHEMISTRY 1978; 92:545-51. [PMID: 153836 DOI: 10.1111/j.1432-1033.1978.tb12776.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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26
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Cohen WS. The coupling of electron flow to ATP synthesis in pea chloroplasts stored in the presence of glycerol at −70°C. ACTA ACUST UNITED AC 1978. [DOI: 10.1016/0304-4211(78)90003-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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27
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Cross-linking within a subunit of coupling factor 1 increases the proton permeability of spinach chloroplast thylakoids. J Biol Chem 1977. [DOI: 10.1016/s0021-9258(17)40926-4] [Citation(s) in RCA: 79] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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28
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Slooten L, Sybesma C. Photoinactivation of photophosphorylation and dark ATPase in Rhodospirillum rubrum chromatophores. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 449:565-80. [PMID: 11818 DOI: 10.1016/0005-2728(76)90165-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Preillumination of Rhodospirillum rubrum chromatophores with strong, far-red light in the presence of phenazine methosulfate under non-phosphorylation conditions results in a selective, irreversible inactivation (typically about 70%) of photophosphorylation and of uncoupler-stimulated dark ATPase. The time course of the photoinactivation is similar to the light-on kinetics of the light-induced proton uptake in the absence of ADP. Only little photoinactivation occurs when the uncoupler carbonyl cyanide m-chlorophenyl hydrazone is present or when phenazine methosulfate is absent during the preillumination, indicating that the reaction occurs only when the membrane is energized. Phosphorylation conditions offer a practically complete protection against the photoinactivation. Inorganic phosphate, Mg2+ or ADP do not provide a significant protection against the photoinactivation, nor does ATP. The pH-dependence of the reaction(s) leading to photoinactivation may indicate that a partial reaction of the photophosphorylation process (perhaps only a conformational change of the coupling factor) precedes the photoinactivation.
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Magnusson RP, McCarty RE. Light-induced exchange of nucleotides into coupling factor 1 in spinach chloroplast thylakoids. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(17)32865-x] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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31
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Oliver D, Jagendorf A. Exposure of free amino groups in the coupling factor of energized spinach chloroplasts. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(17)32958-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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32
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Posorske L, Jagendorf AT. Nucleotide and metal interactions affecting inactivation of spinach chloroplast coupling factor by NaCl in the cold. Arch Biochem Biophys 1976; 177:276-83. [PMID: 999287 DOI: 10.1016/0003-9861(76)90437-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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33
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Horton P, Cramer WA. Stimulation of photosystem I-induced oxidation of chloroplast cytochrome b-559 by pre-illumination and by low pH. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 430:122-34. [PMID: 4140 DOI: 10.1016/0005-2728(76)90228-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
(1) The proportion of higher plant chloroplast cytochrome b-559 oxidizable during illumination by low intensity 732 nm light increases as the pH is decreased below 6.5. At pH 5.0-5.3 total oxidation is seen and subsequent red light can cause reduction of up to 2/3 of the oxidized cytochrome. The oxidation by far red light at pH 5 is inhibited by 2 muM 2,5-dibromo-3-methyl-6-isopropyl-rho-benzoquinone whereas the red light-induced reduction is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. In this pH range ferricyanide-oxidized cytochrome b-559 exists in a form not reducible by ferrocyanide. (2) An increase in the amplitude of far-red induced oxidation also occurs at higher pH (up to pH 7.8) after pre-treatment of chloroplasts with substantially higher levels of light (approx. 10(6) ergs-cm-2-s-1). The degree of light activation is pH dependent, being more pronounced at lower pH. After light activation, cytochrome b-559 can be completely oxidized by far-red light in a manner reversible by red light up to pH values of 6, and the curve describing the amplitude of far-red oxidation as a function of pH is shifted by 0.5-1.0 pH unit toward higher pH. Far-red oxidation and red light reduction are again inhibited by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, respectively. (3) Light activation at pH 5.2-6.0 is also manifested in a small decrease in the amplitude of subsequent dark ferrocyanide reduction, and this decrease is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (10 muM). (4) The effect of intramembranal acidity on the effective redox potential of cytochrome b-559 and its function is discussed.
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Gould JM. Inhibition by triphenyltin chloride of a tightly-bound membrane component involved in photophosphorylation. EUROPEAN JOURNAL OF BIOCHEMISTRY 1976; 62:567-75. [PMID: 131035 DOI: 10.1111/j.1432-1033.1976.tb10191.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
At very low concentrations (less than 1 muM) triphenyltin chloride inhibits ATP formation and coupled electron transport in isolated spinach chloroplasts. Basal (-Pi) and uncoupled electron transport are not affected by triphenyltin. The membrane-bount ATP in equilibrium Pi exchange and Mg2+-dependent ATPase activities of chloroplasts are also completely sensitive to triphenyltin, although the Ca2+-dependent and Mg2+-dependent ATPase activities of the isolated coupling factor protein are insensitive to triphenyltin. The light-driven proton pump in chloroplasts is stimulated (up to 60%) by low levels of triphenyltin. Indeed, the amount of triphenyltin necessary to inhibit ATP formation or stimulate proton uptake is dependent upon the amount of chloroplasts present in the reaction mixture, with an apparent stoichiometry of 2-2.5 triphenyltin molecules/100 chlorophyll molecules at 50% inhibition of ATP formation and half-maximal stimulation of proton uptake. Chloroplasts partially stripped of coupling factor by an EDTA was are no longer able to accumulate protons in the light. However, low levels of triphenyltin can effectively restore this ability. The amount of triphenyltin required for the restoration of net proton uptake is also dependent upon the amount of chloroplasts, with a stoichiometry of 4-5 triphenyltin molecules/100 chlorophyll molecules at 50% reconstitution. On the basis of this and other evidence it is concluded that triphenyltin chloride inhibits phosphorylation, ATP + Pi exchange and membrane-bound ATPase activities in chloroplasts by specifically blocking the transport of protons through a membrane-bound carrier or channel located in a hydrophobic region of the membrane at or near the functional binding site for the coupling factor.
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35
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Portis AR, McCarty RE. Quantitative relationships between phosphorylation, electron flow, and internal hydrogen ion concentrations in spinach chloroplasts. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(17)33692-x] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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