Time resolved EPR on photosystem II particles after irreversible and reversible inhibition of water cleavage with high concentrations of acetate

Abstract Electron transfer in irreversibly acetate-inhibited PS II preparations from Synechococcus is investigated with EPR. A 1.4 mT wide EPR line with a decay rate consistent with the P + 680 Q − A back reaction is tentatively assigned to be a broadened P + 680 spectrum. With reversible inhibition of water cleavage by the ADRY reagent FCCP added with acetate electron transfer is studied as well. Under these conditions the spectrum of the immediate donor to P + 680 is the same as the spectrum of Z + in systems with irreversibly inhibited water cleavage (signal II fast) and the same as that of D + (signal II slow). The consequences are discussed.