Kinetic Modelling of Processes Behind S _2, 3 -states Deactivation in Photosynthetic Oxygen Evolution

Photosynthetic water splitting, localized in photosystem II, is the source of atmospheric oxygen and possible alternative energy source. It is therefore important to understand the related processes which influence the efficiency of water splitting. We have employed kinetic models of photosystem II to study deactivation processes of higher S-states (redox states of water splitting) in the dark. Our analysis of spinach samples, treated or untreated by electron acceptor phenylparabenzoquinone (PPBQ) indicated an unknown mechanism, decay, related to S\(_{2,3}\)-state deactivation. We concluded that: (1) S\(_3\)-state decay occurs independently on the PPBQ treatment, i.e., independently on the redox state of the acceptor side of photosystem II, (2) S\(_2\)-state decay can be fully described by S\(_2\)-\(Q^{-}_{A,B}\) charge recombination, neglected in previous models, and (3) the mechanism of S\(_3\)-state decay can be explained by the involvement of slow cooperation within photosystem II dimer between S\(_3\) PSIIa and S\(_{3,2,1}\) PSIIb in higher plants. Finally, the slow cooperation is able to explain experimental data both from PPBQ-free and PPBQ treated samples.