Flash-induced relaxation changes of the EPR signals from the manganese cluster and YD reveal a light-adaptation process of Photosystem II

Research output: Contribution to journalArticle

Abstract

By exposing photosystem II (PSII) samples to an incrementing number of excitation flashes at room temperature, followed by freezing, we could compare the Mn-derived multiline EPR signal from the S-2 oxidation state as prepared by 1, 5, 10, and 25 flashes of light. While the S-2 multiline signals exhibited by these samples differed very little in spectral shape, a significant increase of the relaxation rate of the signal was detected in the multiflash samples as compared to the S-2-state produced by a single oxidation. A similar relaxation rate increase was observed for the EPR signal from Y-D(.). The temperature dependence of the multiline spin-lattice relaxation rate is similar after 1 and 5 flashes. These data are discussed together with previously reported phenomena in terms of a light-adaptation process of PSII, which commences on the third flash after dark-adaptation and is completed after 10 flashes. At room temperature, the fast-relaxing, light-adapted state falls back to the slow-relaxing, dark-adapted state with t(1/2) = 80 s. We speculate that light-adaptation involves changes necessary for efficient continuous water splitting. This would parallel activation processes found in many other large redox enzymes, such as Cytochrome c oxidase and Ni-Fe hydrogenase. Several mechanisms of light-adaptation are discussed, and we find that the data may be accounted for by a change of the PSII protein matrix or by the light-induced appearance of a paramagnetic center on the PSII donor side. At this time, no EPR signal has been detected that correlates with the increase of the relaxation rates, and the nature of such a new paramagnet remains unclear. However, the relaxation enhancement data could be used, in conjunction with the known Mn-Y-D distance, to estimate the position of such an unknown relaxer. If positioned between Y-D and the Mn cluster, it would be located 7-8 Angstrom from the spin center of the S-2 multiline signal.

Details

Authors
  • Sindra Peterson Årsköld
  • Karin A Åhrling
  • Joakim Högblom
  • Stenbjörn Styring
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biochemistry and Molecular Biology

Keywords

  • MULTILINE SIGNAL, SATURATION-RECOVERY EPR, SPIN-LATTICE RELAXATION, PHOTOSYNTHETIC O2 EVOLUTION, OXYGEN-EVOLVING COMPLEX, S-2 STATE, ELECTRON-PARAMAGNETIC-RESONANCE, IRON-SULFUR PROTEINS, DYSPROSIUM COMPLEXES, INDUCED ENHANCEMENTS
Original languageEnglish
Pages (from-to)2748-2758
JournalBiochemistry
Volume42
Issue number9
Publication statusPublished - 2003
Publication categoryResearch
Peer-reviewedYes