Comparative Analysis of the Interaction of the Primary Quinone Q in Intact and Mn-Depleted Photosystem II Membranes Using Light-Induced ATR-FTIR Spectroscopy

In photosystem II, redox potential E of primary quinone Q shifts by approximately +150 mV upon inactivation of the MnCaO cluster. Although this phenomenon is important in photoprotection, the molecular mechanism of the positive E(Q/Q) shift remains unclear. Here, we investigated the effect of Mn depletion on the interaction of Q using light-induced ATR-FTIR spectroscopy. It was shown that Mn depletion hardly changed a Q/Q FTIR difference spectrum, indicating that the H-bond interaction of Q and its immediate surroundings were virtually unchanged by MnCaO cluster inactivation. On the basis of this result, a possible mechanism of the E(Q/Q) shift is discussed.