The long term goal of this research is to characterize in molecular detail the nature of biological oxidation-reduction reactions. Specifically, we will investigate the active sites of manganoproteins involved in the biological production of dioxygen. These enzymes include the Mn cluster in the Oxygen Evolving Complex of Photosystem II, a Mn-containing catalase, and Mn superoxide dismutase and one electron chemistry of dioxygen. XAS will be used in conjunction with other spectroscopic methods to probe the structure of the Mn active sites of these enzymes.