Photosystem II energy coupling in chloroplasts with H2O2 as electron donor |
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Authors: | RL Pan S Izawa |
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Institution: | Department of Biology, Wayne State University, Detroit, MI 48202, U.S.A. |
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Abstract: | NH2OH-treated, non-water-splitting chloroplasts can oxidize H2O2 to O2 through Photosystem II at substantial rates (100–250 μequiv · h?1 · mg?1 chlorophyll with 5 mM H2O2) using 2,5-dimethyl-p-benzoquinone as an electron acceptor in the presence of the plastoquinone antagonist dibromothymoquinone. This H2O2 → Photosystem II → dimethylquinone reaction supports phosphorylation with a ratio of 0.25–0.35 and proton uptake with values of 0.67 (pH 8)–0.85 (pH 6). These are close to the value of 0.3–0.38 and the values of 0.7–0.93 found in parallel experiments for the H2O → Photosystem II → dimethylquinone reaction in untreated chloroplasts. Semi-quantitative data are also presented which show that the donor → Photosystem II → dibromothymoquinone (→O2) reaction can support phosphorylation when the donor used is a proton-releasing reductant (benzidine, catechol) but not when it is a non-proton carrier (I?, ferrocyanide). |
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Keywords: | Photosystem II Energy coupling Hydrogen peroxide Dibromothymoquinone Electron transport DBMIB DCMU 3-(3 4-dichlorophenyl)-1 1-dimethylurea Hepes Mes |
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