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Formation Spectra of the EPR Split Signals from the S(0), S(1), and S(3) States in Photosystem II Induced by Monochromatic Light at 5 K
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
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2007 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 46, no 37, 10703-10712 p.Article in journal (Refereed) Published
Abstract [en]

The interaction EPR split signals from photosystem II (PSII) have been reported from the S0, S1, and S3 states. The signals are induced by illumination at cryogenic temperatures and are proposed to reflect the magnetic interaction between YZ* and the Mn4Ca cluster. We have investigated the formation spectra of these split EPR signals induced in PSII enriched membranes at 5 K using monochromatic laser light from 400 to 900 nm. We found that the formation spectra of the split S0, split S1, and split S3 EPR signals were quite similar, but not identical, between 400 and 690 nm, with maximum formation at 550 nm. The major deviations were found between 440 and 480 nm and between 580 and 680 nm. In the regions around 460 and 680 nm the amplitudes of the formation spectra were 25-50% of that at 550 nm. A similar formation spectrum was found for the S2-state multiline EPR signal induced at 0 degrees C. In general, the formation spectra of these signals in the visible region resemble the reciprocal of the absorption spectra of our PSII membranes. This reflects the high chlorophyll concentration necessary for the EPR measurements which mask the spectral properties of other absorbing species. No split signal formation was found by the application of infrared laser illumination between 730 and 900 nm from PSII in the S0 and S1 states. However, when such illumination was applied to PSII membranes poised in the S3 state, formation of the split S3 EPR signal was observed with maximum formation at 740 nm. The quantum yield was much less than in the visible region, but the application of intensive illumination at 830 nm resulted in accumulation of the signal to an amplitude comparable to that obtained with illumination with visible light. The split S3 EPR signal induced by NIR light was much more stable at 5 K (no observable decay within 60 min) than the split S3 signal induced by visible light (50% of the signal decayed within 30 min). The split S3 signals induced by each of these light regimes showed the same EPR spectral features and microwave power saturation properties, indicating that illumination of PSII in the S3 state by visible light or by NIR light produces a similar configuration of YZ* and the Mn4Ca cluster.

Place, publisher, year, edition, pages
2007. Vol. 46, no 37, 10703-10712 p.
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:uu:diva-11415DOI: 10.1021/bi7004174ISI: 000249433100030PubMedID: 17718509OAI: oai:DiVA.org:uu-11415DiVA: diva2:39184
Available from: 2007-09-12 Created: 2007-09-12 Last updated: 2017-12-11Bibliographically approved
In thesis
1. EPR Studies of Photosystem II: Characterizing Water Oxidizing Intermediates at Cryogenic Temperatures
Open this publication in new window or tab >>EPR Studies of Photosystem II: Characterizing Water Oxidizing Intermediates at Cryogenic Temperatures
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The principles of natures own light-driven water splitting catalyst, Photosystem II (PSII), can in the future inspire us to use water as electron and proton source to generate light-driven H2 production. To mimic this challenging step, it is important to understand how the enzyme system can oxidize water. The mechanism of light-driven water oxidation in PSII is in this thesis addressed by EPR spectroscopy. P680+ is a strong oxidant formed by light-oxidation of the chlorophyll species P680 positioned in the center of PSII. The redox active tyrosine-Z (YZ) can reduce P680+ and the YZ radical is formed. This transient radical is further reduced by the CaMn4-cluster, which is the binding site of the substrate water molecules. In a cyclic process called the S-cycle, this catalytic cluster accumulates four oxidizing equivalents to evolve one molecule of O2 and to oxidize two molecules of water. We can induce the YZ radical at cryogenic temperatures in the different oxidation states of the catalytic S-cycle and observe this in metalloradical EPR signals. These metalloradical EPR signals are here characterized and used to deduce mechanistic information from the intact PSII. The "double nature" of these spin-spin interaction signals, so called split EPR signals, makes them excellent probes to both YZ oxidation and, when YZ is present, also to the S-states of the CaMn4-cluster. The metalloradical EPR signals presented here, form a way to study the transient YZ radical in active PSII that has not been depleted of the catalytic metal cluster. This depleting method that has often been used in the past to study YZ is not representing studies of a mechanistically relevant material. The previously suggested disorder around YZ and accessibility to the bulk can be artifactual properties induced in the mechanistically defect PSII. On the contrary, our observation that proton coupled electron transfer from YZ to the light induced P680+ can occur in a high yield at cryogenic temperatures, suggests a well ordered catalytic site in the protein positioned for optimal performance. The optimized positioning of the redox components found in PSII might be a feature also important to build in an efficient water oxidizing catalyst.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 72 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 621
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:uu:diva-99109 (URN)978-91-554-7458-4 (ISBN)
Public defence
2009-04-24, Häggsalen, Ångströmslabortoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
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Available from: 2009-04-03 Created: 2009-03-09 Last updated: 2010-01-13Bibliographically approved

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Ho, Felix M.Han, GuangyeMamedov, FikretStyring, Stenbjörn

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