Characterisation of Triplet and Quinone Induced Cation Radical States in the Isolated Photosystem Two Reaction Centre

Transient absorption spectroscopy has been used to study isolated Photosystem 2 (PS2) reaction centres stabilised by the use of anaerobic conditions. In the absence of added artificial electron donors and acceptors, the light induced electron transfer properties of the reaction centre are restricted to the formation of the radical pair P680+Pheophytin− and charge recombination pathways from this state [1]. This charge recombination has been observed to produce a 23% yield of a chlorophyll triplet state [1]. Attempts to reconstitute these particles with quinone have until now been limited to the observation of a steady state, quinone-mediated photoreduction of the cytochrome b-559 [2].