Dual-mode EPR study of new signals from the S3-state of oxygen-evolving complex in photosystem II

The light-induced new EPR signals at g = 12 and 8 were observed in photosystem II (PS II) membranes by parallel polarization EPR. The signals were generated after two flashes of illumination at room temperature, and the signal intensity had four flashes period oscillation, indicating that the signal origin could be ascribed to the S-3-state, Successful simulations were obtained assuming S = 1 spin for the values of the zero-field parameters, D = +/-0.435 +/- 0.005 cm(-1) and E/D = -0.317 +/- 0.002, Orientation dependence of the g = 12 and 8 signal intensities shows that the axial direction of the zero-field interaction of the manganese cluster is nearly parallel to the membrane normal.