Increased Superoxide Production in the Cytochrome B6F Complex: A Function for the Enigmatic Chlorophyll-A (original) (raw)
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Biophysical Journal, 2013
wild-type RBS COX; however, the a-region of the reduced spectrum for E90H(SIII) displayed a slight red shift of the absorbance maximum by 1 nm, resembling that seen for the SIII-depleted oxidase. E90H(III) and E90H/ H212(III) mutant proteins were determined to contain stoichiometric amount of each subunit by SDS-PAGE gel, similar to wild-type COX. Electron transfer rates observed at pH 6.5, for E90H(III)/H212E(III) and E90H(SIII) COX, were decreased by 17 and 39% respectively, as compared to WT COX. The mutants exhibit little or no suicide inactivation when compared to the SIII-depleted RBS COX. pH dependence of electron transfer activity for E90H(III)/ H212E(III) and E90H(III) were also not altered when compared to WT enzyme. Proton pumping experiments on reconstituted E90H(III) and E90H(III)/ H212E(III) in liposomes will be discussed.
An Anhydrous Proton Transfer Pathway in the Cytochrome B6F Complex
Biophysical Journal, 2013
wild-type RBS COX; however, the a-region of the reduced spectrum for E90H(SIII) displayed a slight red shift of the absorbance maximum by 1 nm, resembling that seen for the SIII-depleted oxidase. E90H(III) and E90H/ H212(III) mutant proteins were determined to contain stoichiometric amount of each subunit by SDS-PAGE gel, similar to wild-type COX. Electron transfer rates observed at pH 6.5, for E90H(III)/H212E(III) and E90H(SIII) COX, were decreased by 17 and 39% respectively, as compared to WT COX. The mutants exhibit little or no suicide inactivation when compared to the SIII-depleted RBS COX. pH dependence of electron transfer activity for E90H(III)/ H212E(III) and E90H(III) were also not altered when compared to WT enzyme. Proton pumping experiments on reconstituted E90H(III) and E90H(III)/ H212E(III) in liposomes will be discussed.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1967
Light-induced absorbance changes of cytochromes b and f in chloroplasts have been measured in the cytochrome a-band region with a dual-wavelength spectrophotometer. The data indicate that there are b-type cytochromes at two different places in the electron-transport system. Whereas the cytochrome f changes induced by red (645 m/~) and far-red (715 m/z) light are typical of the two pigment system antagonism, the cytochrome b changes are more complex. With an actinic light intensity of 2-3"10 4 ergs.cm-2.sec-1 and no electron acceptor, the cytochrome b changes show two components, with difference spectra peaking at 563 and 56o m/~, respectively. Cytochrome b-563 is associated with a fast transient reduction upon illumination with far-red light. On turning off the far-red, cytochrome b-56o shows an oxidation which is reversible by red light. Cytochrome b-563 is oxidized in the dark and is not reduced by ascorbate, whereas cytochrome b-56o, when oxidized, is ascorbate reducible. Both components are reduced by NADPH via a diaphorase. The cytochrome b-56o shows red, far-red reversibility at lower actinic light intensities and in the presence of carbonylcyanide m-chlorophenylhydrazone. It is concluded that cytochrome b-563 is reduced by Photosystem I and that cytochrome b-56o is in the electron transport chain between Photosystems i and 2. IN'[RODUCTION The existence of b-type cytochrome in the chloroplasts of green plants was first demonstrated by HILL and co-workers 1,2. The participation of cytochrome b in the two light reactions of photosynthesis has been inferred from studies on the green alga, Chlamydomonas reinhardi, and various mutants of it by CHANCE, SCHLEYER AND LEGALLAIS 3, LEVINE et al. 4, and LEVINE AND GORMAN 5 ; on Euglena and the bluegreen alga Anacystis by OLSON AND SMILLIEe; on red algae by NISHIMURAT; and on spinach chloroplasts by RUMBERG 8, HIND AND OLSON °, and BUTLER 1°. Although the existence of cytochrome b in the photosynthetic electron transport chain is well Abbreviations: cyt, cytochrome; DCMU, 3-(3,4-dichlorophenyl)-I,I-dimethylurea; CCCP, carbonylcyanide m-chlorophenylhydrazone. * National Science Foundation postdoctoral fellow.
Generation and scavenging of reactive oxygen species in chloroplasts: a submolecular approach
Agriculture, Ecosystems & Environment, 2005
Wheat (Triticum aestivum L.) plants were subjected to combined waterlogging and shading (WS) at 0-7, 8-15, 16-23 and 24-31 days after anthesis (DAA). WS at 0-7, 8-15, 16-23 and 24-31 DAA caused a yield loss of 17.18%, 14.98%, 7.93% and 7.05%, respectively. These losses were related to reductions in post-anthesis photoassimilate accumulation and 1000-kernel weight. WS reduced net photosynthetic rate (P n), the maximum efficiency of PSII photochemistry under dark adaptation, actual photosynthetic efficiency and the photochemical quenching coefficient, but increased the quantum yield of quenching. WS caused enhanced concentrations of malondialdehyde and H 2 O 2 , and an increased superoxide anion release. Superoxide dismutase and catalase activity were stimulated at 4 days after the onset of WS at 0-7 and 8-15 DAA, but decreased at 8 days after the onset of WS at 0-7, 8-15 and 16-23 DAA. Ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase activity increased during 0-8 days after the onset of WS at 0-7, 8-15 and 16-23 DAA. At 16-24 DAA, P n , the level of reactive oxygen species and activity of the antioxidative enzymes fully recovered in plants subjected to WS at 0-7 DAA, but only partially recovered under WS at 8-15 DAA. Expression of the photosythesis-responsive genes RcaB and Cab, and the antioxidative enzyme-related genes Mn-SOD, Cu/Zn-SOD, CAT and GR were consistent with the performance of P n and the activity of the antioxidative enzymes.
Functional Plant Biology, 2017
Reduction of O2 molecule to superoxide radical, O2•−, in the photosynthetic electron transport chain is the first step of hydrogen peroxide, H2O2, production in chloroplasts in the light. The mechanisms of O2 reduction by ferredoxin, by the components of the plastoquinone pool, and by the electron transfer cofactors in PSI are analysed. The data indicating that O2•− and H2O2 can be produced both outside and within thylakoid membrane are presented. The H2O2 production in the chloroplast stroma is described as a result of either dismutation of O2•− or its reduction by stromal reductants. Formation of H2O2 within thylakoid membrane in the reaction of O2•− with plastohydroquinone is examined. The significance of both ways of H2O2 formation for specificity of the signal being sent by photosynthetic electron transport chain to cell adaptation systems is discussed.
Photooxidation of cytochrome b559 and the electron donors in chloroplast Photosystem II
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1973
The effect of light on the reaction center of Photosystem lI was studied by differential absorption spectroscopy in spinach chloroplasts. At-196 °C, continuous illumination results in a parallel reduction of C-550 and oxidation of cytochrome b559 high potential. With flash excitation, C-550 is reduced, but only a small fraction of cytochrome b559 is oxidized. The specific effect of flash illumination is suppressed if the chloroplasts are preilluminated by one flash at 0 °C. At-50 °C, continuous illumination results in the reduction of C-550 but little oxidation of cytochrome b559. However, complete oxidation is obtained if the chloroplasts have been preilluminated by one flash at 0 °C. The effect of preillumination is not observed in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. A model is discussed for the reaction center, with two electron donors, cytochrome b559 and Z, acting in competition. Their respective efficiency is dependent on temperature and on their states of oxidation. The specific effect of flash excitation is attributed to a two-photon reaction, possibly based on energy-trapping properties of the oxidized trap chlorophyll.