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EPR studies of the oxygen-evolving complex reveal a light-adaption process in Photosystem II

Peterson Årsköld, Sindra LU ; Åhrling, Karin A.; Högblom, Joakim LU and Styring, Stenbjörn LU (2001) In PS2001 Proceedings
Abstract
Photosystem II utilizes solar energy to drive electrons from the Mn cluster at the lumenal side to the quinone at the stromal side of the thylakoid membrane. The source of electrons is H2O, which is split to oxygen by the OEC. The water-splitting process involves cycling of the Mn-cluster through four semi-stable oxidation states, termed the S0, S1, S2, and S3 states. The OEC can be trapped in the different S-states, and studied by EPR techniques.

The S2 state is often obtained by exposing a dark-adapted (S1 state) sample to continuous illumination at low temperature, or to a single flash of light at room temperature followed by freezing. Both procedures capture the S2 state, as reached by a single oxidation of the OEC following a... (More)
Photosystem II utilizes solar energy to drive electrons from the Mn cluster at the lumenal side to the quinone at the stromal side of the thylakoid membrane. The source of electrons is H2O, which is split to oxygen by the OEC. The water-splitting process involves cycling of the Mn-cluster through four semi-stable oxidation states, termed the S0, S1, S2, and S3 states. The OEC can be trapped in the different S-states, and studied by EPR techniques.

The S2 state is often obtained by exposing a dark-adapted (S1 state) sample to continuous illumination at low temperature, or to a single flash of light at room temperature followed by freezing. Both procedures capture the S2 state, as reached by a single oxidation of the OEC following a period of dark-adaptation. With a laser flash procedure, the S2 state can be obtained a second time after 5 flashes, when the S-cycle has been completed once.

We have discovered differences between the S2 state formed after one flash and the S2 state formed after five flashes, in terms of the relaxation behavior of the S2 multiline EPR signal. These data indicate a change within the Mn cluster that builds up during the first turnovers after dark-adaptation. Pulsed field-swept spectra of samples given 0-5 flashes of light show a similar trend: the S1 state obtained by zero and four flashes differ significantly from one another.

Based on the data presented and similar reports in the literature, we propose that the OEC undergoes a light-adaptation process during the first two turnovers after dark-adaptation, adjusting the system for efficient continuous water-splitting. We tentatively suggest that light-adaptation involves rearrangements of the proton network in the OEC, possibly as a means of setting up proton channels. (Less)
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organization
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Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
S-cycle, Oxygen evolution, Manganese, Saturation, Relaxation
in
PS2001 Proceedings
publisher
CSIRO Publishing
ISBN
CD-ROM - 0643067116
language
English
LU publication?
yes
id
17b63d3b-99a4-434f-b9fe-7c12ebc68c38 (old id 527315)
alternative location
http://www.publish.csiro.au/PS2001/cf/search/article.cfm?ID=453065915
date added to LUP
2007-09-24 15:03:24
date last changed
2016-04-16 08:03:58
@inproceedings{17b63d3b-99a4-434f-b9fe-7c12ebc68c38,
  abstract     = {Photosystem II utilizes solar energy to drive electrons from the Mn cluster at the lumenal side to the quinone at the stromal side of the thylakoid membrane. The source of electrons is H2O, which is split to oxygen by the OEC. The water-splitting process involves cycling of the Mn-cluster through four semi-stable oxidation states, termed the S0, S1, S2, and S3 states. The OEC can be trapped in the different S-states, and studied by EPR techniques.<br/><br>
The S2 state is often obtained by exposing a dark-adapted (S1 state) sample to continuous illumination at low temperature, or to a single flash of light at room temperature followed by freezing. Both procedures capture the S2 state, as reached by a single oxidation of the OEC following a period of dark-adaptation. With a laser flash procedure, the S2 state can be obtained a second time after 5 flashes, when the S-cycle has been completed once. <br/><br>
We have discovered differences between the S2 state formed after one flash and the S2 state formed after five flashes, in terms of the relaxation behavior of the S2 multiline EPR signal. These data indicate a change within the Mn cluster that builds up during the first turnovers after dark-adaptation. Pulsed field-swept spectra of samples given 0-5 flashes of light show a similar trend: the S1 state obtained by zero and four flashes differ significantly from one another.<br/><br>
Based on the data presented and similar reports in the literature, we propose that the OEC undergoes a light-adaptation process during the first two turnovers after dark-adaptation, adjusting the system for efficient continuous water-splitting. We tentatively suggest that light-adaptation involves rearrangements of the proton network in the OEC, possibly as a means of setting up proton channels.},
  author       = {Peterson Årsköld, Sindra and Åhrling, Karin A. and Högblom, Joakim and Styring, Stenbjörn},
  booktitle    = {PS2001 Proceedings},
  isbn         = {CD-ROM - 0643067116},
  keyword      = {S-cycle,Oxygen evolution,Manganese,Saturation,Relaxation},
  language     = {eng},
  publisher    = {CSIRO Publishing},
  title        = {EPR studies of the oxygen-evolving complex reveal a light-adaption process in Photosystem II},
  year         = {2001},
}