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

Abstract

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 Si (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 S1 to S−1 occurs over a time period of 20min. The S1 reduction can be largely prevented by adding catalase or by removing O2 from the flow buffer with N2. Importantly, we demonstrate that even at the shortest possible polarization times (40s in our set up) the S2 and S0 decays are significantly accelerated by the side reaction with H2O2. The removal of hydrogen peroxide leads to unperturbed S2 state data that reveal three instead of the traditionally reported two phases of decay. In addition, even under the best conditions (catalase+N2; 40s 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.