This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Measurement of the auto-reduction rate by the x-ray beam was continued for the oxidized form of cytochrome ba3. X-ray diffraction data and single crystal absorption spectra in the UV/Visible region were recorded at ~15 K. Based on these measurements and previous measuremetns, the rate of reduction was reduced by a factor of 2-3 at the lower temperature. Approximetely 2-4 frames could be collected from a single crystal that diffracted to ~3.0 A. Typically, only 1 out of 15 crystals diffract to this resolution requiring approximtely 90/3 X 15 = 450 crystals. Methods to produce a higher yield of good diffracting crystals will be caried out in J. Fee?s laboratory and compaibility of the UV/VIS spectroscopy system and the robotic monting system for highthroughput screeening will be developed at SSRL.