NON-HEME IRON DIOXYGNASES: STRUCTURE AND MECHANISMS

The non-heme iron dioxygenases participate in many metabolic reactions and little is known of the active sites and mechanisms of these enzymes. This research proposes to elucidate the active site structures and mechanisms of some of these enzymes using both spectroscopic and kinetic techniques. Four enzyme systems have been proposed: the intradiol cleaving catechol dioxygenases (catechol 1,2-dioxygenase and protocatechuate 3,4-dioxygenase), the extradiol cleaving catechol dioxygenases (3,4-dihydroxyphenylacetate 2,3-dioxygenase), benzoate 1,2-dioxygenase and soybean lipoxygenase. These enzymes and their various complexes will be probed with optical, EPR, NMR, Mossbauer, resonance Raman and EXAFS spectroscopies to obtain information regarding the oxidation and spin state of the iron, the ligands bound to the iron and molecular details of the mechanism. Kinetic studies (including stopped flow and cryoenzymological techniques) will be employed to isolate enzymatic intermediates and characterize these spectroscopically. The effects of substrate analogues on enzyme activity should provide information on the binding of substrate to the active site. Finally, on the basis of parameters obtained from the spectroscopic studies, iron complexes will be designed and synthesized to mimic active site structure and function.