Flash-induced redox changes in oxygen-evolving spinach Photosystem II core particles |
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Authors: | Peter J van Leeuwen Claudia Heimann Peter Gast Jan P Dekker Hans J van Gorkom |
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Institution: | (1) Department of Biophysics, Huygens Laboratory of the State University, P.O. Box 9504, 2300 RA Leiden, The Netherlands;(2) Department of Physics and Astronomy, Free University, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands |
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Abstract: | Flash-induced redox reactions in spinach PS II core particles were investigated with absorbance difference spectroscopy in the UV-region and EPR spectroscopy. In the absence of artificial electron acceptors, electron transport was limited to a single turnover. Addition of the electron acceptors DCBQ and ferricyanide restored the characteristic period-four oscillation in the UV absorbance associated with the S-state cycle, but not the period-two oscillation indicative of the alternating appearance and disappearance of a semiquinone at the QB-site. In contrast to PS II membranes, all active centers were in state S1 after dark adaptation. The absorbance increase associated with the S-state transitions on the first two flashes, attributed to the Z+S1 ZS2 and Z+S2 ZS3 transitions, respectively, had half-times of 95 and 380 s, similar to those reported for PS II membrane fragments. The decrease due to the Z+S3 ZS0 transition on the third flash had a half-time of 4.5 ms, as in salt-washed PS II membrane fragments. On the fourth flash a small, unresolved, increase of less than 3 s was observed, which might be due to the Z+S0 ZS1 transition. The deactivation of the higher S-states was unusually fast and occurred within a few seconds and so was the oxidation of S0 to S1 in the dark, which had a half-time of 2–3 min. The same lifetime was found for tyrosine D+, which appeared to be formed within milliseconds after the first flash in about 10% inactive centers and after the third and later flashes by active centers in Z+S3.Abbreviations Bis-Tris
(bis2-hydroxyethyl]imino-trishydroxymethyl]methane)
- D
secondary electron donor of PS II
- DCBQ
2,5-dichloro-p-benzoquinone
- DCMU
3-(3 ,4 dichlorophenyl)-1,1-dimethylurea
- PS II
Photosystem II
- QA
secondary electron acceptor of PS II
- S0–3
redox state of the oxygen-evolving complex
- Z
secondary electron donor of PS II |
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Keywords: | Photosystem II PS II core oxygen-evolving complex UV asorbance changes EPR signal II |
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