Dark production of reactive oxygen species in photosystem II membrane particles at elevated temperature: EPR spin-trapping study |
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Authors: | Pavel Pospíšil Iva Šnyrychová Jan Nauš |
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Institution: | Laboratory of Biophysics, Department of Experimental Physics, Faculty of Science, Palacký University, t?. Svobody 26, 771 46 Olomouc, Czech Republic |
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Abstract: | In our study, EPR spin-trapping technique was employed to study dark production of two reactive oxygen species, hydroxyl radicals (OH ) and singlet oxygen (1O2), in spinach photosystem II (PSII) membrane particles exposed to elevated temperature (47 °C). Production of OH , evaluated as EMPO-OH adduct EPR signal, was suppressed by the enzymatic removal of hydrogen peroxide and by the addition of iron chelator desferal, whereas externally added hydrogen peroxide enhanced OH production. These observations reveal that OH is presumably produced by metal-mediated reduction of hydrogen peroxide in a Fenton-type reaction. Increase in pH above physiological values significantly stimulated the formation of OH , whereas the presence of chloride and calcium ions had the opposite effect. Based on our results it is proposed that the formation of OH is linked to the thermal disassembly of water-splitting manganese complex on PSII donor side. Singlet oxygen production, followed as the formation of nitroxyl radical TEMPO, was not affected by OH scavengers. This finding indicates that the production of these two species was independent and that the production of 1O2 is not closely linked to PSII donor side. |
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Keywords: | desferal deferoxamine mesylate DMPO 5 5-Dimethyl-1-pyrroline N-oxide EDTA Ethylenediamine-N N N&prime N&prime -tetraacetic acid EMPO 2-ethoxycarbonyl-2-methyl-3 4-dihydro-2H-pyrrole-1-oxide EPR electron paramagnetic resonance PSII photosystem II ROS reactive oxygen species TEMP 2 2 6 6-tetramethylpiperidine TyrD Tyr-161 of subunit D2 of PSII TyrZ Tyr-161 of subunit D1 of PSII |
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