Are the trapping dynamics in Photosystem II sensitive to Q(A) redox potential?

Removal of the manganese complex from photosystem Il (PSII) causes a 145 me V shift in the redox potential of the plastoquinone Q(A) [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 inta ct and manganese depleted BBY-type core particles studied with Q(A) in a fu lly open state. Surprisingly, no difference is observed between the experim ental results obtained from the intact and manganese depleted samples. We d emonstrate that this could be indicative of a very deep primary radical pai r trap formed in PSII core particles with Q(A) in a fully open state. Alter natively, static inhomogeneity or a possible time-dependence of the Q(A) re dox potential via relaxations such as proton motions should be considered. (C) 2001 Elsevier Science B.V. All rights reserved.