title: Spectroscopic evidence for a heme-superoxide/Cu(I) intermediate in a functional model of cytochrome c oxidase.
abstract: A superstructured tetraphenylporphyrin with a covalently attached proximal imidazole axial base and three distal imidazole pickets has been developed as a model for the active site of terminal oxidases such as cytochrome c oxidase. The oxygen adduct of the Fe-only heme (at low temperature) has a diamagnetic NMR and is EPR silent, which taken together with a resonance Raman oxygen isotope sensitive band (nuFe-O) at 575/554 cm-1 (16O2/18O2) indicates formation of a six-coordinate heme-superoxide complex. Unexpectedly, the Fe/Cu complex, where the copper is in a trisimidazole environment approximately 5 A above the heme plane, displays similar characteristics: a diamagnetic NMR, EPR silence, and nuFe-O at 570/544 cm-1. This indicates the dioxygen adduct of this Fe/Cu system is also a superoxide. This contrasts with previously characterized partially reduced dioxygen intermediates of binuclear heme/copper complexes that form Fe/Cu mu-peroxo complexes.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA. jpc@stanford.edu
authors.forename: James P
authors.initials: JP
authors.lastname: Collman
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Sunderland
authors.forename: Katja E
authors.initials: KE
authors.lastname: Berg
authors.forename: Michael A
authors.initials: MA
authors.lastname: Vance
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D013481:Superoxides / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D013481:Superoxides; C000499:ferric oxide; D006418:Heme; D003300:Copper; D003576:Electron Transport Complex IV; D010100:Oxygen