The primary objective of the proposed research is to gain a better understanding of how important metal containing enzymes work. Three Ni- contain enzymes that catalyze environmentally important processes, hydrogenase, methyl-Com reductase, and CO dehydrogenase have been chosen for investigation. The molecular structures of the first two of these enzymes have been solved by x-ray crystallography. However, important questions remain about the electronic structure of the Ni sites in all three enzymes under different conditions. The catalytic mechanisms are still poorly understood. It is proposed to study the electronic structure of the Ni sites under different conditions using soft x-ray absorption and x-ray magnetic circular dichroism spectroscopy. Analysis of the spectra can provide quantitative information about where the electrons are in transition metal complexes. The molecular structure around the Ni sites will also be studied, using extended x-ray absorption fine structure (EXAFS) analysis. Although there is a considerable body of literature concerning the EXAFS of these enzymes, much of the work was done with limited signal-to-noise or before there was a full appreciation of sample heterogeneity. New samples with more homogenous Ni sites will be prepared using recently developed biochemistry. Better spectra will be taken by using more concentrated samples and a faster detector. A deeper knowledge of the structure and mechanism of these enzymes will enrich the field of bioinorganic chemistry. Metalloproteins play many roles in normal health and disease states of human beings. A better understanding of how proteins modulate the properties of Ni metal ions will assist our understanding of other metals as well. Further, the spectroscopic being developed are broadly applicable.
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