Electron paramagnetic resonance study of the magnetic structure of the S1-state in oriented oxygen evolving photosystem II membranes

The S-1-state of the oxygen evolving complex was studied in oriented photosystem II membranes by parallel polarization electron paramagnetic resonance (EPR) spectroscopy. The EPR intensity, ascribed to the S-1-state Mn-cluster with S = 1, varies depending on the magnetic field direction relative to the membrane normal: maximum and minimum were observed at angles of 0 and 90 degrees, respectively. Successful simulations of line shape and intensity observed in the non-oriented and the oriented membranes were obtained using the values of the zero-field parameter, D = +/- 0.14 +/- 0.01 cm(-1) and E/D = - 0.11 +/- 0.02, by assuming an isotropic g-value of 2.0. The anisotropy in EPR intensity shows that the axial direction of the zero-field interaction of the manganese cluster is almost parallel to the membrane plane. (C) 1999 Elsevier Science B.V. All rights reserved.