X-RAY-DETECTION OF THE PERIOD-4 CYCLING OF THE MANGANESE CLUSTER IN PHOTOSYNTHETIC WATER OXIDIZING ENZYME

X-ray absorption near-edge structure spectra of the manganese (Mn) cluster in physiologically native intermediate states of photosynthetic water oxidation induced by short laser flash were measured with a compact heat-insulated chamber equipped with an x-ray detector near the sample surface. The half-height energy of the Mn K-edge showed a period-four oscillation dependent on cycling of the Joliot-Kok's oxygen clock. The flash number-dependent shift in the Mn K-edge suggests that the Mn cluster is oxidized by one electron upon the S0-to-S1, S1-to-S2, and S2-to-S3 transitions and then reduced upon the S3-to-S0 transition that releases molecular oxygen.