title: Mono- and bis-phosphine-ligated H93G myoglobin: spectral models for ferrous-phosphine and ferrous-CO cytochrome P450.
abstract: To further investigate the properties of phosphines as structural and functional probes of heme proteins, mono- and bis-phosphine [tris(hydroxymethyl)phosphine, THMP] adducts of H93G myoglobin (Mb) have been prepared by stepwise THMP titrations of exogenous ligand-free ferric and ferrous H93G Mb, respectively. Bubbling with CO or stepwise titration with imidazole (Im) of the bis-THMP-ligated ferrous protein generated a mixed ligand (THMP/CO or THMP/Im, respectively) ferrous complexes. Stable oxyferrous H93G(THMP) Mb was formed at -40°C by bubbling the mono-THMP-Fe(II) protein with O2. A THMP-ligated ferryl H93G Mb moiety has been partially formed upon addition of H2O2 to the ferric mono-THMP adduct. All the species prepared above have been characterized with UV-visible (UV-vis) absorption and magnetic circular dichroism (MCD) spectroscopy in this study. The six-coordinate ferrous bis-phosphine and mono-phosphine/CO complexes of H93G Mb exhibit characteristic spectral features (red-shifted Soret/unique-shaped MCD visible bands and hyperporphyrin spectra, respectively) that only have been seen for the analogous phosphine or CO-complexes of thiolate-ligated heme proteins such as cytochrome P450 (P450) and Caldariomyces fumago chloroperoxidase (CPO). However, such resemblance is not seen in phosphine-ligated ferric H93G Mb even though phosphine-bound ferric P450 and CPO display hyperporphyrin spectra. In fact, bis-THMP-bound ferric H93G Mb exhibits MCD and UV-vis absorption spectra that are similar to those of bis-amine- and bis-thioether-ligated H93G Mb complexes. This study also further demonstrates the utility of the H93G cavity mutant for preparing novel heme iron coordination structures.
authors: Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA.
authors: Shengfang
authors: S
authors: Sun
authors: Masanori
authors: M
authors: Sono
authors: John H
authors: JH
authors: Dawson
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D008954:Models, Biological; D015394:Molecular Structure; D010720:Phosphines / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D005296:Ferrous Compounds; D010720:Phosphines; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; C044646:phosphine
keywords: Heme iron model complexes; Hyperporphyrin spectra; Magnetic circular dichroism spectroscopy; Phosphine as heme axial ligand; Tris(hydroxymethyl)phosphine-bound H93G myoglobin