The electron paramagnetic resonance characterization of ferrous nitrosyl non-heme iron models and enzymes
Non-heme iron oxygenases represent a class of enzyme that activate dioxygen and catalyze a diverse range of thermodynamically challenging reactions. Phenylalanine hydroxylase(PheH) is a non-heme Fe enzyme that catalyzes the hydroxylation of the C4 position of the phenol side chain of phenylalanine(phe) to yield tyrosine and Tyrosine hydroxylase(TyrH) catalyzes the hydroxylation of the C3 position of the phenol side chain of tyrosine(tyr) to yield L-DOPA. These two enzymes contain a highly conserved iron binding motif termed the facial triad with 2 histidine ligands and a carboxylate facially coordinating the iron. This work focuses on the EPR characterization of these two enzymes and a series of model complexes containing the same N, N, O facial binding motif. The catalytically relevant oxidation state for non-heme iron oxygenases is Fe(II) which is EPR silent, this problem was overcome by studying Fe(II)-NO complexes where the NO acts as an oxygen surrogate and couples to the Fe(II) generating an EPR active S=3/2 system. Using 2H electron spin echo envelope modulation(ESEEM) sepectroscopy we have shown that in TyrH and PheH there is a structural change that occurs in the active site upon substrate addition which results in movement of the pterin co-susbtrate closer to the Fe(II) center. 2H ESEEM has also shown that in TyrH and PheH a change in the orientation of the Fe-NO bond with respect primary substrate occurs on co-substrate binding. Hyperfine sub-level correlation spectroscopy was used to characterize the magnetic environment of the model complexes including the chelating ligand and solvent molecules. These results were applied to aid in the understanding of the HYSCORE spectra collected on TyrH and PheH.
0488: Inorganic chemistry
0494: Physical chemistry