Electrochemically produced hydrogen peroxide affects Joliot-type oxygen-evolution measurements of photosystem II

The main technique employed to characterize the efficiency of water-splitting in photosynthetic preparations in terms of miss and double hit parameters and for the determination of S-i (i = 2,3,0) state lifetimes is the measurement of flash-induced oxygen oscillation pattern on bare platinum (Joliot-type) electrodes. We demonstrate here that this technique is not innocent. Polarization of the electrode against an Ag/AgCl electrode leads to a time-dependent formation of hydrogen peroxide by two-electron reduction of dissolved oxygen continuously supplied by the flow buffer. While the miss and double hit parameters are almost unaffected by H2O2, a time dependent reduction of S-1 to S-1 occurs over a time period of 20 mm. The S-1 reduction can be largely prevented by adding catalase or by removing O-2 from the flow buffer with N-2. Importantly, we demonstrate that even at the shortest possible polarization times (40 s in our set up) the S-2 and S-0 decays are significantly accelerated by the side reaction with H2O2. The removal of hydrogen peroxide leads to unperturbed S-2 state data that reveal three instead of the traditionally reported two phases of decay. In addition, even under the best conditions (catalase + N-2; 40 s polarization) about 4% of S-1 state is observed in well dark-adapted samples, likely indicating limitations of the equal fit approach. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy. (C) 2014 Elsevier B.V. All rights reserved.