Light-dependent reduction of hydrogen peroxide by intact spinach chloroplasts |
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Authors: | JW Anderson Christine H Foyer DA Walker |
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Institution: | ARC Research Group on Photosynthesis, Department of Botany, University of Sheffield, Sheffield S10 2TN U.K. |
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Abstract: | Intact spinach chloroplasts, washed four times in buffered sorbitol to decrease catalase contamination, supported O2 evolution in the dark at very low rates (less than 2 μmol/mg Chl per h) in the presence of low concentrations of H2O2 (0.25 mM); H2O2 was not significantly metabolished under these conditions. In the light, washed chloroplasts supported H2O2-dependent O2 evolution at rates of 28–46 μmol/mg Chl per h in the presence of 0.1–0.25 mM H2O2; the concentration of H2O2 supporting 0.5Vmax was estimated to be 25 μM. O2 evolution in the light was associated with H2O2 consumption and ceased after the production of 0.45 mol per mol H2O2 consumed. Both O2 evolution and H2O2 consumption were abolished by 5 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Washed intact chloroplasts contained endogenous pools of GSH and ascorbate estimated at 10 and 33 mM, respectively. H2O2-dependent O2 evolution in the light was associated with a decrease in these levels which increased as O2 evolution gradually ceased. The results are consistent with the hypothesis that H2O serves as eventual electron donor for the reduction of H2O2 in illuminated chloroplasts and that GSH/GSSG and ascorbate/dehydroascorbate serve as intermediate electron carriers. Preincubation of chloroplasts in the dark with 0.1 mM H2O2 abolished O2 evolution in the light. |
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Keywords: | Hydrogen peroxide reduction Oxygen evolution Glutathione metabolism Ascorbate metabolism Catalase (Spinach chloroplast) Chl chlorophyll DCMU 3-(3 4-dichlorophenyl)-1 1-dimethylurea Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid |
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