A XANES study of the manganese complex of inhibited PS II membranes indicates manganese redox changes between the modified S 1, S 2 and S 3 states

Abstract

Manganese K-edge X-ray spectra have been obtained for Photosystem II samples treated to inhibit oxygen evolution without displacement of manganese. Inhibition treatments included the use of ammonia, acetate and high concentrations of sodium chloride. These treatments affect the binding of calcium and chloride cofactors and result in either a block or slowing of OEC S-state cycling at the S 3 → S 0 transition. Following each inhibition treatment the S-states show characteristic K-edge energies and EPR spectra. The differences between each type of inhibitory treatment in the K-edge energy for each S-state may result from conformational and/or ligand changes to the manganese complex. However for each of the inhibitory treatments, the K-edge energies showed edge shifts between S-states consistent with manganese oxidation on both the S 1 → S 2 and S 2 → S 3 transitions.