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The formation of the split EPR signal from the S(3) state of Photosystem II does not involve primary charge separation
Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany. (Molecular Biomimetics, Department of Photochemistry and Molecular Science, Uppsala University, The Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden)
Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui, 230026, China. (Molecular Biomimetics, Department of Photochemistry and Molecular Science, Uppsala University, The Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden)
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Molecular Biomimetics, Department of Photochemistry and Molecular Science, Uppsala University, The Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden)
Molecular Biomimetics, Department of Photochemistry and Molecular Science, Uppsala University, The Ångström Laboratory, P.O. Box 523, S-751 20 Uppsala, Sweden.
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2011 (English)In: Biochimica et Biophysica Acta, ISSN 0006-3002, E-ISSN 1878-2434, Vol. 1807, no 1, 11-21 p.Article in journal (Refereed) Published
Abstract [en]

Metalloradical EPR signals have been found in intact Photosystem II at cryogenic temperatures. They reflect the light-driven formation of the tyrosine Z radical (Y(Z)) in magnetic interaction with the CaMn(4) cluster in a particular S state. These so-called split EPR signals, induced at cryogenic temperatures, provide means to study the otherwise transient Y(Z) and to probe the S states with EPR spectroscopy. In the S(0) and S(1) states, the respective split signals are induced by illumination of the sample in the visible light range only. In the S(3) state the split EPR signal is induced irrespective of illumination wavelength within the entire 415-900nm range (visible and near-IR region) [Su, J. H., Havelius, K. G. V., Ho, F. M., Han, G., Mamedov, F., and Styring, S. (2007) Biochemistry 46, 10703-10712]. An important question is whether a single mechanism can explain the induction of the Split S(3) signal across the entire wavelength range or whether wavelength-dependent mechanisms are required. In this paper we confirm that the Y(Z) radical formation in the S(1) state, reflected in the Split S(1) signal, is driven by P680-centered charge separation. The situation in the S(3) state is different. In Photosystem II centers with pre-reduced quinone A (Q(A)), where the P680-centered charge separation is blocked, the Split S(3) EPR signal could still be induced in the majority of the Photosystem II centers using both visible and NIR (830nm) light. This shows that P680-centered charge separation is not involved. The amount of oxidized electron donors and reduced electron acceptors (Q(A)(-)) was well correlated after visible light illumination at cryogenic temperatures in the S(1) state. This was not the case in the S(3) state, where the Split S(3) EPR signal was formed in the majority of the centers in a pathway other than P680-centered charge separation. Instead, we propose that one mechanism exists over the entire wavelength interval to drive the formation of the Split S(3) signal. The origin for this, probably involving excitation of one of the Mn ions in the CaMn(4) cluster in Photosystem II, is discussed.

Place, publisher, year, edition, pages
Elsevier , 2011. Vol. 1807, no 1, 11-21 p.
Keyword [en]
Photosystem II, EPR, S3 state, Near-infrared, Split signal
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-45410DOI: 10.1016/j.bbabio.2010.09.006PubMedID: 20863810OAI: oai:DiVA.org:umu-45410DiVA: diva2:429391
Available from: 2011-07-04 Created: 2011-07-04 Last updated: 2017-12-11Bibliographically approved

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