Pham Long Vo, Messinger Johannes
Department of Chemistry, Chemistry Biology Center (KBC), Umeå University, Linnaeus väg 6, SE-901 87 Umeå, Sweden.
Department of Chemistry, Chemistry Biology Center (KBC), Umeå University, Linnaeus väg 6, SE-901 87 Umeå, Sweden.
Biochim Biophys Acta. 2014 Sep;1837(9):1411-6. doi: 10.1016/j.bbabio.2014.01.013. Epub 2014 Jan 29.
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 20 min. 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.
