GM65440 Renewal Resubmission Project Summary The element iron plays an enormous role in biology, including electron transport reactions (ferredoxins), oxygen transport and storage (hemoglobin and myoglobin), catalysis (nitrogenase, P-450, hydrogenase, and thousands of other enzymes), small molecule sensing (especially O2, CO, and NO), and DNA processing and repair. The health-relatedness of a better understanding of the structure and function of biological Fe is clear. The general theme of research in the Cramer lab involves the use spectroscopy as a tool for characterization of metals in biological systems. Much of this work involves the application of synchrotron radiation x-ray sources. Thanks to enormous improvements of these sources, experiments with exquisite sensitivity can now be conducted on dilute Fe samples. This includes the technique Nuclear Resonance Vibrational Spectroscopy (NRVS), which is sensitive to the motion of 57Fe in a sample. The x-ray experiments at international facilities are complemented by IR and Raman measurements at the home lab. One particular home-based experiment will involve pump-probe spectroscopy of sample in cryosolvents at temperatures down to -100°C. A Nd:YAG OPO combination will be used to pump the sample (initiate photochemistry) and a quantum cascade laser (QCL) or FT-IR will be used to probe the subsequent reaction products. The goals for the next 4 years can be divided into 2 major themes: · better understanding of the catalytic intermediates of the enzymes that process hydrogen – [NiFe] and [FeFe] hydrogenases, and · information about structural changes that occur when Fe-S cluster proteins sense their environment, including mitoNEET and NAF-1, two health-related proteins which sense and communicate pH and redox status. The overall vision of this research program is to use spectroscopic methods to better understand how iron is used in important proteins, in ways that complement the information that can be gathered from diffraction and microscopy. In the course of research on specific topics, spectroscopic techniques will be further developed for the bioinorganic community.