title: The detection of two electron paramagnetic resonance radical signals associated with chloroperoxidase compound I.
abstract: The electron paramagnetic resonance spectra of chloroperoxidase Compound I and native enzyme are compared. Upon the formation of Compound I, the g = 2.62, 2.26, and 1.82 signals associated with native enzyme disappear and are replaced by two new EPR signals, a sharp signal at g = 2.008 and a broad signal at g = 1.73. The g = 2.008 signal accounts for only 2% of the theoretical spins while the broad signal at g = 1.73 accounts for 60 to 70% of the theoretical spins in Compound I. The g = 1.73 broad signal is reminiscent of the broad EPR signal associated with horseradish peroxidase Compound I. however, the chloroperoxidase Compound I signal has a significantly different g value. The results suggest that the g = 1.73 signal represents a porphyrin pi cation radical which has a stronger coupling to the heme ferryl iron than is the case with horseradish peroxidase Compound I.
mesh_terms: D002711:Chloride Peroxidase / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007700:Kinetics; D046911:Macromolecular Substances; D003904:Mitosporic Fungi / Q000201:enzymology*; D010544:Peroxidases / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D046911:Macromolecular Substances; D010544:Peroxidases; D002711:Chloride Peroxidase