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The photosystem II-associated Cah3 in Chlamydomonas enhances the O-2 evolution rate by proton removal
Umea Univ, Dept Plant Physiol, Umea Plant Sci Ctr, S-90187 Umea, Sweden.
Univ Osnabruck, Dept Biophys, Osnabruck, Germany.
Free Univ Berlin, Dept Phys, D-1000 Berlin, Germany.
Russian Acad Sci, Inst Basic Biol Problems, Pushchino 142292, Russia.
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2008 (English)In: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 27, no 5, 782-791 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2008. Vol. 27, no 5, 782-791 p.
Keyword [en]
carbonic anhydrase, Chlamydomonas reinhardtii, photosystem II, proton removal, water oxidation
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-45905DOI: 10.1038/emboj.2008.12OAI: diva2:266801
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2010-05-24

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