Spectroscopic Studies of Mononuclear Non-Heme Fe Enzymes

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DESCRIPTION (provided by applicant): Mononuclear non-heme iron enzymes catalyze a wide range of reactions which either involve O2 activation by a high-spin ferrous site or substrate activation by a high-spin ferric site. Recently a class of non-heme iron enzymes that has thiolate ligation has also been defined. These enzymes are directly related to genetic disorders (phenylketonuria, alkaptonuria), involved in the biosynthesis of antibiotics, lactamase inhibitors, and leukotrienes and lipoxins, important in the repair of DNA alkylation damage, and utilized in the treatment of certain cancers. Non-heme iron enzymes have generally been far more difficult to study than heme enzymes. New spectroscopic methods (emphasizing variable-temperature, variable-field magnetic circular dichroism, and metal K- and L-edge and ligand K-edge X-ray absorption spectroscopy) have been and are being developed which enable the detailed study of these enzymes. Density functional theory calculations supported by these spectroscopic data provide further insight into electronic structure and allow evaluation of reaction coordinates. The goals of this research are to: 1) directly probe the ferrous active sites and their interactions with substrate, cofactor and other relevant factors to elucidate catalytic mechanisms on a molecular level; 2) understand how cosubstrate binding initiates the reaction of the ferrous center with O2; 3) experimentally and theoretically understand the nature of oxygen intermediates and factors that control their reactivity; 4) determine how non-heme relates to heme iron in activating O2; 5) understand the nature of substrate activation by an oxidized iron center, and define the factor(s) leading to selectivity in aromatic ring cleavage; 6) determine the contributions of the highly covalent thiolate S-Fe(lll) bond to the different reactivities of the cysteine liganded non-heme iron enzymes. RELEVANCE: The non-heme iron enzymes are associated with a wide range of diseases including arteriosclerosis, cancer (regulation of hypoxia) and neurological disorders (Alzheimer's, Parkinson's, etc.). These enzymes are also extremely important in the treatment and prevention of disease due to their roles in the biosynthesis of antibiotics (penicillins, cephalosporins, vancomycin), anti-cancer activity (Bleomycin), DNA repair and the bioremediation of pollutants (including PCBs). These studies provide a fundamental understanding of the modes of action of these enzymes enabling strategies to improve or inhibit function and enhance drug design.