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EPR and optical changes of the photosystem II reaction center produced by low temperature illumination |
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| Authors: | Harry A Frank Örjan Hansson Paul Mathis |
| Institution: | (1) Service de Biophysique, Département de Biologie, Centre d'Etudes Nucléaires de Saclay, 91191 Gif-sur-Yvette, Cedex, France;(2) Department of Chemistry, University of Connecticut, 215 Glenbrook Road, U-60, 06268 Storrs, Connecticut, USA;(3) Department of Biochemistry and Biophysics, Chalmers Institute of Technology, S-41296 Göteborg, Sweden;(4) University of Göteborg, S-41296 Göteborg, Sweden |
| Abstract: | Electron paramagnetic resonance (EPR) and absorption spectroscopy have been used to study the low temperature photochemical behavior of the Photosystem II D-1/D-2/ cytochrome b559 reaction center complex. The reaction center displays large triplet state EPR signals which are attenuated after actinic illumination at low temperatures in the presence of sodium dithionite. Concomitant with the triplet attenuation is the buildup of a structured radical signal with an effective g value of 2.0046 and a peak-to-peak width of 11.9 G. The structure in the signal is suggestive of it being comprised in part of the anion radical of pheophytin a. This assignment is corroborated by low temperature optical absorbance measurements carried out after actinic illumination at the low temperatures which show absorption bleachings at 681 nm, 544 nm and 422 nm and an absorbance buildup at 446 nm indicating the formation of reduced pheophytin.Abbreviations EPR electron paramagnetic resonance |
| Keywords: | electron paramagnetic resonance electron transfer pheophytin photosystem II radical triplet state |
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