The photosystem II-associated Cah3 in Chlamydomonas enhances the O 2 evolution rate by proton removal

Tatiana Shutova, Hella Kenneweg, Joachim Buchta, Julia Nikitina, Vasily Terentyev, Sergey Chernyshov, Bertil Andersson, Suleyman I. Allakhverdiev, Vyacheslav V. Klimov, Holger Dau, Wolfgang Junge, Göran Samuelsson

Research output: Contribution to journalArticlepeer-review

79 Citations (Scopus)


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 O2 evolution in the absence of HCO3-. The O2 evolution for saturating, continuous illumination (RO2) was slower than in the wild type, but was elevated by HCO3 - and increased further by Cah3. The RO2 limitation in the absence of Cah3/HCO3- was amplified by H 2O/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 O2-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 O2 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.

Original languageEnglish
Pages (from-to)782-791
Number of pages10
JournalEMBO Journal
Issue number5
Publication statusPublished - Mar 5 2008
Externally publishedYes


  • Carbonic anhydrase
  • Chlamydomonas reinhardtii
  • Photosystem II
  • Proton removal
  • Water oxidation

ASJC Scopus subject areas

  • General Neuroscience
  • Molecular Biology
  • General Biochemistry,Genetics and Molecular Biology
  • General Immunology and Microbiology


Dive into the research topics of 'The photosystem II-associated Cah3 in Chlamydomonas enhances the O 2 evolution rate by proton removal'. Together they form a unique fingerprint.

Cite this