Berlin 2005 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 30: POSTER: Chemical physics
CPP 30.24: Poster
Tuesday, March 8, 2005, 16:30–18:30, Poster TU D
Transient EPR Study of Electron Transfer in Photosystem I: A0 to A1(Anthraquinone) to FX — •Irina Karyagina1, Yulia Pushkar2, and Dietmar Stehlik1 — 1Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany — 2Calvin Laboratory, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720-5230
In Photosystem I (PS I) phylloquinone (PhQ) acts as a low potential electron acceptor during light induced electron transfer (ET). The origin of the very low midpoint potential is investigated by introducing the lower potential acceptor anthraquinone (AQ) into the A1 site of PS I in the presence and absence of the partial negative charge on the iron-sulphur clusters (FeS). Using multi-frequency transient EPR spectroscopy, structural and dynamic properties of the sequential radical pair (RP) states are investigated. The orientation of AQ in all samples is the same as that of PhQ in native PS I. The kinetics show: (i) ET from the second to the third RP is faster from AQ than from PhQ to FeS as expected from the more negative reduction midpoint potential of AQ. (ii) By the same change of midpoint potential the preceding ET step from the first to the second RP is slowed down. The lifetime of the first RP state is observed to lengthen with increasing temperature. This unusual temperature dependence and the observed changes in spin polarisation pattern are explained by a model based on a distribution of lifetimes/midpoint redox potentials of A0.