Effect of the redox state of QB on electric field-induced charge recombination in Photosystem II

Electric field-induced charge recombination in Photosystem II (PS II) was studied in osmotically swollen spinach chloroplasts (blebs) by measurement of the concomitant chlorophyll luminescence emission (electroluminescence). A pronounced dependence on the redox state of the two-electron gate Q_B was observed and the earlier failure to detect it is explained. The influence of the Q_B/Q_B^– oscillation on electroluminescence was dependent on the redox state of the oxygen evolving complex; at times around one millisecond after flash illumination a large effect was observed in the states S₂ and S₃, but not in the state S₄ (actually Z⁺S₃). The presence of the oxidized secondary electron donor, tyrosine Z⁺, appeared to prevent expression of the Q_B/Q_B^– effect on electroluminescence, possibly because this effect is primarily due to a shift of the redox equilibrium between Z/Z⁺ and the oxygen evolving complex.Abbreviations BSA bovine serum albumin - EDTA ethylene-diaminetetraacetic acid - EL electroluminescence - FCCP carbonylcyanide p-trifluoromethyloxyphenyl-hydrazone - HEPESI 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - I primary electron acceptor - MOPS 3-(N-morpholino) propane sulfonic acid - P680 primary electron donor of Photosystem II - P700 primary electron donor of Photosystem I - Q_A and Q_B secondary and tertiary electron acceptors of Photosystem II - Z secondary electron donor (D1 Tyr 161)