Spectroscopic evidence for a heme-superoxide/Cu(I) intermediate in a functional model of cytochrome c oxidase.
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.
Collman
James P
JP
Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA. jpc@stanford.edu
Sunderland
Christopher J
CJ
Berg
Katja E
KE
Vance
Michael A
MA
Solomon
Edward I
EI
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
D005290:Ferric Compounds; D013481:Superoxides; C000499:ferric oxide; D006418:Heme; D003300:Copper; D003576:Electron Transport Complex IV; D010100:Oxygen