title: EPR studies on compound I of horseradish peroxidase.
abstract: Compound I of horseradish peroxidase (donor: hydrogen-peroxide oxidoreductase EC 1.11.1.7) was studied by EPR at low temperatures. An asymmetric signal was found, about 15 Gauss wide and with a g-value of 1.995, which could be detected only at temperatures below 20 K and which had an intensity corresponding to about 1% of the heme content. In a titration with H2O2, the signal intensity was proportional to the concentration of Compound I, reaching a maximum when equivalent amounts of H2O2 were added. This indicates that the signal is not due to an impurity, and it is suggested that a free radical is formed, relaxed by a near-by fast-relaxing iron.
mesh_terms: D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D005615:Freezing; D006418:Heme / Q000032:analysis; D006861:Hydrogen Peroxide; D007700:Kinetics; D010544:Peroxidases; D010944:Plants / Q000201:enzymology*; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D006418:Heme; D006861:Hydrogen Peroxide; D010544:Peroxidases