Time-resolved structure determinations are at the forefront of attempts to understand the mechanisms of protein reactions. X-ray absorption spectroscopy (XAS) provides a window on the environment of specific atoms in chemical and biological systems, and is well suited to examining the chemistry of metal atoms in biological milieu. In addition, XAS can be applied to a wide range of sample phases, and can successfully probe the chemical environment of a wide range of atoms in the periodic table (from low Z atoms, like sulfur, to heavy atoms, like third row transition metals). We are developing a system for collecting high quality x-ray absorption spectroscopy data on s and longer timescales. The method can be used for both full spectra accumulation and kinetic spectrophotometry. Experiments using this technology have vast potential, not only for examining metalloproteins, but also for observing the dynamic behavior of a wide range of chemical elements in conjunciton with photo-chemical, rapid mixing, and temperature jump techniques. We have tested the system by examining the structural evolution of the myoglobin-carbon monoxide complex after photolysis at low temperature.
