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

Manganese K-edge X-ray spectra have been obtained for Photosystem II s amples treated to inhibit oxygen evolution without displacement of man ganese. Inhibition treatments included the use of ammonia, acetate and high concentrations of sodium chloride. These treatments affect the b inding of calcium and chloride cofactors and result in either a block or slowing of OEC S-state cycling at the S3 --> S0 transition. Followi ng each inhibition treatment the S-states show characteristic K-edge e nergies and EPR spectra. The differences between each type of inhibito ry treatment in the K-edge energy for each S-state may result from con formational and/or ligand changes to the manganese complex. However fo r each of the inhibitory treatments, the K-edge energies showed edge s hifts between S-states consistent with manganese oxidation on both the S1 --> S2 and S2 --> S3 transitions.