Production of reactive oxygen species in decoupled, Ca2+-depleted PSII and their use in assigning a function to chloride on both sides of PSII
| Autor: | Michael Seibert, K. N. Timofeev, I. I. Ivanov, Andrei B. Rubin, L. N. Davletshina, Boris K. Semin |
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| Rok vydání: | 2013 |
| Předmět: |
Light
Photosystem II Inorganic chemistry macromolecular substances Plant Science Oxygen-evolving complex Photochemistry Biochemistry Chloride Substrate Specificity chemistry.chemical_compound Chlorides Spinacia oleracea Superoxides medicine Amino Acids Hydrogen peroxide chemistry.chemical_classification Hydroxyl Radical Cytochromes c Photosystem II Protein Complex Water food and beverages Substrate (chemistry) Hydrogen Peroxide Cell Biology General Medicine Hydrogen-Ion Concentration Electron acceptor Electron transport chain Oxygen Membrane chemistry 2 6-Dichloroindophenol Calcium Reactive Oxygen Species Oxidation-Reduction medicine.drug |
| Zdroj: | Photosynthesis Research. 117:385-399 |
| ISSN: | 1573-5079 0166-8595 |
| DOI: | 10.1007/s11120-013-9870-x |
| Popis: | Extraction of Ca(2+) from the oxygen-evolving complex of photosystem II (PSII) in the absence of a chelator inhibits O2 evolution without significant inhibition of the light-dependent reduction of the exogenous electron acceptor, 2,6-dichlorophenolindophenol (DCPIP) on the reducing side of PSII. The phenomenon is known as "the decoupling effect" (Semin et al. Photosynth Res 98:235-249, 2008). Extraction of Cl(-) from Ca(2+)-depleted membranes (PSII[-Ca]) suppresses the reduction of DCPIP. In the current study we investigated the nature of the oxidized substrate and the nature of the product(s) of the substrate oxidation. After elimination of all other possible donors, water was identified as the substrate. Generation of reactive oxygen species HO, H2O2, and O 2 (·-) , as possible products of water oxidation in PSII(-Ca) membranes was examined. During the investigation of O 2 (·-) production in PSII(-Ca) samples, we found that (i) O 2 (·-) is formed on the acceptor side of PSII due to the reduction of O2; (ii) depletion of Cl(-) does not inhibit water oxidation, but (iii) Cl(-) depletion does decrease the efficiency of the reduction of exogenous electron acceptors. In the absence of Cl(-) under aerobic conditions, electron transport is diverted from reducing exogenous acceptors to reducing O2, thereby increasing the rate of O 2 (·-) generation. From these observations we conclude that the product of water oxidation is H2O2 and that Cl(-) anions are not involved in the oxidation of water to H2O2 in decoupled PSII(-Ca) membranes. These results also indicate that Cl(-) anions are not directly involved in water oxidation by the Mn cluster in the native PSII membranes, but possibly provide access for H2O molecules to the Mn4CaO5 cluster and/or facilitate the release of H(+) ions into the lumenal space. |
| Databáze: | OpenAIRE |
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