In this project, jointly funded by the Physical Chemistry and Biophysics Programs, X-ray absorption techniques for high resolution studies of metal ion centers in biologically important molecules will be developed. Specific attention will be paid to developing direct probes of covalence in iron- and copper-containing proteins. %%% Nitrogenase, the enzyme responsible for converting atmospheric nitrogen to ammonia, is one of nature's major sources of fertilizer. Detailed chemical understanding of the biological process by which this conversion is accomplished brings us closer to the goal of economical and environmentally benign fertilizer production. This project, by developing X-ray methods of determining structure and bonding in the relevant enzymes, may lead to major breakthroughs in this effort.