The photosystem II-associated Cah3 in Chlamydomonas enhances the O-2 evolution rate by proton removal
Autor(en): | Shutova, Tatiana Kenneweg, Hella Buchta, Joachim Nikitina, Julia Terentyev, Vasily Chernyshov, Sergey Andersson, Bertil Allakhverdiev, Suleyman I. Klimov, Vyacheslav V. Dau, Holger Junge, Wolfgang Samuelsson, Goran |
Stichwörter: | BICARBONATE; Biochemistry & Molecular Biology; carbonic anhydrase; CARBONIC-ANHYDRASE ACTIVITY; Cell Biology; Chlamydomonas reinhardtii; ELECTRON-TRANSFER; FLUORESCENCE; MOLECULAR-MECHANISM; PHOTOSYNTHETIC OXYGEN EVOLUTION; photosystem II; proton removal; QUANTITATIVE ASSESSMENT; REACTION CYCLE; THYLAKOID MEMBRANE; WATER OXIDATION | Erscheinungsdatum: | 2008 | Herausgeber: | WILEY | Journal: | EMBO JOURNAL | Volumen: | 27 | Ausgabe: | 5 | Startseite: | 782 | Seitenende: | 791 | Zusammenfassung: | Water oxidation in photosystem II ( PSII) is still insufficiently understood and is assumed to involve HCO3-. A Chlamydomonas mutant lacking a carbonic anhydrase associated with the PSII donor side shows impaired O-2 evolution in the absence of HCO3-. The O-2 evolution for saturating, continuous illumination (R-O2) was slower than in the wild type, but was elevated by HCO3- and increased further by Cah3. The R-O2 limitation in the absence of Cah3/HCO3- was amplified by H2O/D2O exchange, but relieved by an amphiphilic proton carrier, suggesting a role of Cah3/HCO3- in proton translocation. Chlorophyll fluorescence indicates a Cah3/HCO3- effect at the donor side of PSII. Time-resolved delayed fluorescence and O-2-release measurements suggest specific effects on proton-release steps but not on electron transfer. We propose that Cah3 promotes proton removal from the Mn complex by locally providing HCO3-, which may function as proton carrier. Without Cah3, proton removal could become rate limiting during O-2 formation and thus, limit water oxidation under high light. Our results underlie the general importance of proton release at the donor side of PSII during water oxidation. |
ISSN: | 02614189 | DOI: | 10.1038/emboj.2008.12 |
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