title: Oxoiron(IV) in chloroperoxidase compound II is basic: implications for P450 chemistry.
abstract: With the use of x-ray absorption spectroscopy, we have found that the Fe-O bond in chloroperoxidase compound II (CPO-II) is much longer than expected for an oxoiron(IV) (ferryl) unit; notably, the experimentally determined bond length of 1.82(1) A accords closely with density functional calculations on a protonated ferryl (Fe(IV)-OH, 1.81 A). The basicity of the CPO-II ferryl [pKa > 8.2 (where Ka is the acid dissociation constant)] is attributable to strong electron donation by the axial thiolate. We suggest that the CPO-II protonated ferryl is a good model for the rebound intermediate in the P450 oxygenation cycle;with elevated pKa values after one-electron reduction, thiolate-ligated ferryl radicals are competent to oxygenate saturated hydrocarbons at potentials that can be tolerated by folded polypeptide hosts.
authors.affiliation: Department of Chemistry, Pennsylvania State University, PA 16802, USA. mtg10@psu.edu
authors.forename: Michael T
authors.initials: MT
authors.lastname: Green
authors.forename: John H
authors.initials: JH
authors.lastname: Dawson
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002711:Chloride Peroxidase / Q000737:chemistry* / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000378:metabolism; D004583:Electrons; D005583:Fourier Analysis; D005609:Free Radicals; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism; D006838:Hydrocarbons / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006900:Hydroxylation; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011522:Protons; D013057:Spectrum Analysis
chemical_list: D005609:Free Radicals; D006838:Hydrocarbons; D008024:Ligands; D009942:Organometallic Compounds; D011522:Protons; C066317:ferryl iron; D003577:Cytochrome P-450 Enzyme System; D007501:Iron; D006735:Horseradish Peroxidase; D002711:Chloride Peroxidase; D010100:Oxygen