IN-SITU UV/VIS SPECTROSCOPY FOR MACROMOLECULAR CRYSTALLOGRAPHY

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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. The goal of this project is to enable the simultaneous acquisition of x-ray diffraction data and single crystal absorption spectra in the UV/Visible and infrared regions. Analysis of the absorption spectrum in the UV (190 - 400 nm) and visible (400 - 800 nm) regions provides information about the electronic state of proteins while in the crystalline state. During diffraction experiments, spectroscopic measurements were analyzed to confirm the redox state. Future experiments will include detecting the presence of reaction intermediates or to potentially monitor degradation products that may be produced either by photolysis or by x-rays. A single crystal microspectrophotometer was set up on BL11-1 to record spectra from crystals on the goniometer. Positioning of the optics and a 2nd microscope were refined for ease of use. Data were collected from crystals containing an Fe porphyrin that showed degradation of the oxidation state after 5 degrees of x-ray data. A complete data set was collected from 12 crystals each providing approximately 5 degrees of data. The resulting structure¿s oxidation state could be unambiguously characterized. Based on these experiments, the instrument design is now being optimized further.