Are the trapping dynamics in Photosystem II sensitive to QA redox potential?

Removal of the manganese complex from photosystem II (PSII) causes a 145 meV shift in the redox potential of the plastoquinone QA [Biochim. Biophys. Acta 1229 (1995) 193; Photosynthetica 27 (1–2) (1992) 89; Biochim. Biophys. Acta 1229 (1995) 202]. Time resolved single photon counting has been used to monitor the time dependent concentrations of the singlet states in intact and manganese depleted BBY-type core particles studied with QA in a fully open state. Surprisingly, no difference is observed between the experimental results obtained from the intact and manganese depleted samples. We demonstrate that this could be indicative of a very deep primary radical pair trap formed in PSII core particles with QA in a fully open state. Alternatively, static inhomogeneity or a possible time-dependence of the QA redox potential via relaxations such as proton motions should be considered.