title: Light absorption, electron paramagnetic resonance and resonance Raman characteristics of nitridochromium(V) protoporphyrin-IX and its reconstituted hemoproteins.
abstract: A surprisingly stable complex of the photolyzed product of azidochromium(III)protoporphyrin-IX was prepared and examined by light absorption, electron paramagnetic resonance (EPR) and resonance Raman spectroscopies. The characteristic EPR spectrum for this complex was consistent with a nitridochromium(V)-porphyrin complex which was two oxidation equivalents above the resting Cr(III) complex. The Cr(V)-N stretching mode was observed at 1010 cm-1 by resonance Raman spectroscopy. A simple diatomic harmonic oscillation model gave a force constant of 6.7 mdyn/A for the Cr(V)-N bond, in the region characteristic for the metal-nitrogen triple bond. Nitridochromium(V) protoporphyrin-IX reconstituted myoglobin and cytochrome c peroxidase were prepared for the first time. The nitridochromium(V)-porphyrins in these apo-proteins were unstable in contrast with the protein-free chromium(V)porphyrin. Upon irradiation of the azide complexes of the chromium(III) protoporphyrin-IX reconstituted myoglobin and cytochrome c peroxidase with ultraviolet light aerobically at room temperature, the characteristic optical and EPR spectra for nitridochromium(V) derivatives were observed. The optical spectra of these photo-induced products were different from those of the nitridochromium(V) protoporphyrin-IX reconstituted hemoproteins. The electrochemical structures of the unusual metalloporphyrin seemed to be modulated by the heme surrounding amino acid residues.
authors.affiliation: Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Hori
authors.forename: M
authors.initials: M
authors.lastname: Tsubaki
authors.forename: N T
authors.initials: NT
authors.lastname: Yu
authors.forename: T
authors.initials: T
authors.lastname: Yonetani
mesh_terms: D002857:Chromium; D003578:Cytochrome-c Peroxidase / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D009211:Myoglobin / Q000737:chemistry; D011524:Protoporphyrins / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
chemical_list: D009211:Myoglobin; D011524:Protoporphyrins; D002857:Chromium; C028025:protoporphyrin IX; D003578:Cytochrome-c Peroxidase