S-state dependence of the miss probability in Photosystem II |
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Authors: | Rik de Wijn Hans J van Gorkom |
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Institution: | (1) Department of Biophysics, Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands |
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Abstract: | The oxygen production of dark-adapted Photosystem II upon illumination by a series of single-turnover flashes shows a damped
period four oscillation with flash number. The damping is attributed to `misses' resulting from a statistical probability
that a reaction center fails to produce a stable charge separation after a saturating flash. The origin of misses is of interest
because its probable dependence on flash number, in principle, affects the quantitative interpretation of all measurements
on phenomena associated with the period four oscillation. We show that the kinetics of chlorophyll fluorescence yield transients
induced by a flash series can be used to estimate the relative amplitudes of the miss probability on each flash. It is concluded
that a major part of the misses must be caused by failure of the reduction of the oxidized primary electron donor chlorophyll
P680+ by the secondary donor tyrosine YZ before the charge separation is lost by recombination. The probability of this failure is found to increase with the oxidation
state of the oxygen-evolving complex: more than half of it occurs upon charge separation in the S3 state, which is attributed to the presence of YZ
ox S2 in Boltzmann equilibrium with YZS3.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | charge recombination fluorescence yield miss probability oxygen evolution Photosystem II S-states |
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