Enhancement of Y-D(center dot) spin relaxation by the CaMn4 cluster in photosystem II detected at room temperature: A new probe for the S-cycle

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The long-lived, light-induced radical Y-D(.) of the Tyr161 residue in the D2 protein of Photosystem 11 (PSII) is known to magnetically interact with the CaMn4 cluster, situated similar to 30 angstrom away. In this study we report a transient step-change increase in YD EPR intensity upon the application of a single laser flash to S, state-synchronised PSII-enriched membranes from spinach. This transient effect was observed at room temperature and high applied microwave power (100 mW) in samples containing PpBQ, as well as those containing DCMU. The subsequent decay lifetimes were found to differ depending on the additive used. We propose that this flash-induced signal increase was caused by enhanced spin relaxation of YD by the OEC in the S-2 state, as a consequence of the single laser flash turnover. The post-flash decay reflected S-2 -> S-1 back-turnover, as confirmed by their correlations with independent measurements of S-2 multiline EPR signal and flash-induced variable fluorescence decay kinetics under corresponding experimental conditions. This flash-induced effect opens up the possibility to study the kinetic behaviour of S-state transitions at room temperature using YD as a probe. (c) 2006 Elsevier B.Z. All rights reserved.


  • Felix M. Ho
  • Susan F Morvaridi
  • Fikret Mamedov
  • Stenbjörn Styring
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences


  • S-state transitions, oxygen evolving complex, photosystem II, EPR, tyrosine D, spin relaxation
Original languageEnglish
Pages (from-to)5-14
JournalBiochimica et Biophysica Acta - Bioenergetics
Issue number1
Publication statusPublished - 2007
Publication categoryResearch