High-efficiency oxygen evolution by photosystem II oxygen-evolving complex containing 3Mn per reaction center.

Ca-depleted photosystem II membranes obtained by treatment with acidic buffer do not contain Ca in the MnCaO cluster but contain all extrinsic proteins protecting this cluster (PSII(-Ca/low pH)). However, unlike native photosystem II, Mn cluster in PSII(-Ca/low pH) samples is available for small-sized reductants. Using this property, we investigated the substitution possibility of Mn cation(s) with Fe cation(s) to obtain a chimeric cluster in PSII(-Ca/low pH) samples containing extrinsic proteins. We found that Fe(II) cation replaces Mn cation at pH 6.5, however, PSII(-Ca/low pH) membranes with the 3Mn1Fe chimeric cluster in the oxygen-evolving complex evolve O with high intensity in the presence of exogenous Ca. The O evolution rate is about 80% of the same rate in PSII(-Ca/low pH) membranes.