My research is focused on elucidating the structure and function of metalloenzymes using a combination of X-ray methods. The main emphasis is on understanding the mechanism of light-driven water oxidation in Photosystem II, a large membrane protein present in all organisms that conduct oxygenic photosynthesis. For this purpose, we use very intense femtosecond X-ray pulses as delivered by the X-ray free electron laser, Linac Coherent Light Source (LCLS), at Stanford. This technique allows us to record X-ray diffraction and X-ray spectroscopic data from the enzyme under working (physiological) conditions and provide information about the geometric and electronic structure of the catalytic site (a Mn4CaO5 cluster) of the enzyme during the water oxidation reaction. Also, we are working on generalizing these approaches to other metalloenzymes to study reaction intermediates not accessible with conventional X-ray methods.