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 Ca2+ in the Mn4CaO5 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-2 with high intensity in the presence of exogenous Ca2+. The O-2 evolution rate is about 80% of the same rate in PSII(-Ca/low pH) membranes. [GRAPHICS]

Automated summary

Ca-depleted photosystem II membranes obtained by treatment with acidic buffer lack Ca2+ in the Mn4CaO5 cluster, but contain all extrinsic proteins protecting this cluster (PSII(-Ca/low pH)). Unlike native photosystem II, the Mn cluster in PSII(-Ca/low pH) samples can be reduced by small-sized reductants. By substituting Mn cation(s) with Fe cation(s) at pH 6.5, a chimeric cluster (3Mn1Fe) was obtained in PSII(-Ca/low pH) membranes containing extrinsic proteins. The resulting membranes exhibited high intensity O-2 evolution in the presence of exogenous Ca2+, reaching about 80% of the rate in PSII(-Ca/low pH) membranes.