title: Electron-nuclear double resonance of horseradish peroxidase compound I. Detection of the porphyrin pi-cation radical.
abstract: Electron-nuclear double resonance spectra of horseradish peroxidase Compound I exhibit resonances from 14N and beta-protons, and most probably alpha-protons as well. The measurements prove that the oxyferryl iron of this enzymic intermediate is spin-coupled to a porphyrin radical. Comparison of experimentally obtained average pi-electron spin densities with theoretical predictions for a 4-fold symmetric porphyrin pi-cation radical is supportive of a 2A2u assignment for the radical's electronic state.
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006735:Horseradish Peroxidase; D007527:Isoenzymes; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D010544:Peroxidases; D011166:Porphyrins / Q000032:analysis*; D011485:Protein Binding; D011487:Protein Conformation; D013113:Spin Labels
chemical_list: D005609:Free Radicals; D007527:Isoenzymes; D046911:Macromolecular Substances; D011166:Porphyrins; D013113:Spin Labels; D006735:Horseradish Peroxidase; D010544:Peroxidases