Slow oxygen release on the first two flashes in chemically stressed Photosystem II membrane fragments results from hydrogen peroxide oxidation |
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Authors: | Shinichi Taoka Paul A Jursinic Michael Seibert |
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Institution: | (1) National Renewable Energy Laboratory, 1617 Cole Boulevard, 80401-3393 Golden, CO, USA;(2) Northern Regional Research Center, USDA-Agricultural Research Service, 61604 Peoria, IL, USA;(3) Present address: Department of Biochemistry, University of Nebraska, 68588 NE, Lincoln, USA;(4) Present address: Department of Radiation Oncology, Bronson Methodist Hospital, 49007 Kalamazoo, MI, USA |
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Abstract: | Flash-induced amperometric signals were measured with a Joliot-type O2 rate electrode in spinach Photosystem II (PS II) membrane fragments exposed to very low concentrations of added hydroxylamine or hydrogen peroxide. In both cases anomalous O2 signals were observed on the first two flashes, and oscillating four-flash patterns were observed on subsequent flashes. The anomalous signals were eliminated in the presence of catalase but not EDTA. The rise times of the O2-release kinetics associated with the anomalous signals were slow (ca. 20 ms with NH2OH and ca. 120 ms with H2O2) compared to the kinetics of O2 release on subsequent flashes and in control membranes (3–6 ms). It is proposed that when the intact PS II O2-evolving complex is perturbed with small concentrations of added reductant, H2O2 can gain access and bind to the complex. Bound H2O2 can then reduce lower S states in some centers leading to anomalous O2 signals on the first two flashes. A model is presented to explain both types of anomalous O2 production. Oxygen observed on the third and subsequent flashes is due to the normal photosynthetic O2-evolution process arising from the S3-state. Anomalous O2 production could be a protective mechanism in PS II centers subjected to stress conditions.Abbreviations DCIP
2,6-dichlorophenolindophenol
- EDTA
ethylenediaminetetraacetic acid
- MES
4-morpholine-ethanesulfonic acid
- OEC
oxygen-evolving complex
- PS II
Photosystem II
- Yi
O2 flash yield on the ith flash
- Yss
steady-state O2 flash yield level in algae, chloroplasts, or thylakoids after flash-driven S-state oscillations have been damped
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Keywords: | hydrogen peroxide hydroxylamine kinetics manganese oxygen release photosynthesis Photosystem II |
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