Lawrence Berkeley National Laboratory

In natural photosynthesis, the water oxidation reaction takes place in the oxygen evolving complex (OEC) in Photosystem II (PSII), that cycles through a series of five intermediate S-states. Mechanistic studies of this catalytic reaction have been carried out with various spectroscopic methods, structural analysis, and theoretical studies. Among them, the structural information of the metal cluster has been obtained largely from the X-ray techniques that include X-ray crystallography and X-ray spectroscopy. This chapter describes the recent studies of the OEC in PSII with X-ray spectroscopy and crystallography.