title: Electron paramagnetic and electron nuclear double resonance of the hydrogen peroxide compound of cytochrome c peroxidase.
abstract: We have collected electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectra from the hydrogen peroxide compound of yeast cytochrome c peroxidase, termed ES, employing EPR microwave frequencies of 9.6 and 11.6 GHz. We have measured and analyzed the temperature dependence of the spin-lattice relaxation rate (1/T1) of the paramagnetic center of ES over the temperature range 1.9 to 4 K. In addition, an upper bound to exchange coupling between the ferryl heme and EPR-visible centers of ES has been calculated and expressions for the dipolar interaction between a ferryl heme and a free radical have been derived. These results all confirm that the EPR signal of ES is not associated with an aromatic amino acid radical, and in particular not with a tryptophanyl radical. This conclusion has led us to consider an explanation of the EPR signal in terms of a nucleophilically stabilized methionyl radical.
mesh_terms: D001665:Binding Sites; D003578:Cytochrome-c Peroxidase; D004578:Electron Spin Resonance Spectroscopy; D006861:Hydrogen Peroxide; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D010544:Peroxidases; D011485:Protein Binding; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000201:enzymology
chemical_list: D006861:Hydrogen Peroxide; D010544:Peroxidases; D003578:Cytochrome-c Peroxidase