title: Magnetic circular dichroism studies of the active site structure of hemoprotein H-450: comparison to cytochrome P-450 and sensitivity to pH effects.
abstract: Ferric, ferrous and ferrous-CO hemoprotein H-450 from rat liver have been examined with magnetic circular dichroism spectroscopy under alkaline (pH 8.0) and acidic (pH 6.0) conditions. The spectral properties of these species require that one of the axial heme iron ligands in the alkaline ferric and ferrous states must be a thiolate sulfur, presumably from cysteine. The data are most consistent with the ligand trans to thiolate being either histidine or methionine. The reversible pH effects on the spectral properties of the ferrous protein, but not of the ferric protein, appear to involve protonation or displacement of the thiolate. As treatment of the ferrous protein with CO does not yield a thiolate-ligated ferrous-CO adduct, CO either displaces the thiolate or its addition is accompanied by protonation of the thiolate.
authors.affiliation: Department of Chemistry, University of South Carolina, Columbia 29208.
authors.forename: E W
authors.initials: EW
authors.lastname: Svastits
authors.forename: J A
authors.initials: JA
authors.lastname: Alberta
authors.forename: I C
authors.initials: IC
authors.lastname: Kim
authors.forename: J H
authors.initials: JH
authors.lastname: Dawson
mesh_terms: D000818:Animals; D001665:Binding Sites; D019475:Camphor 5-Monooxygenase; D002248:Carbon Monoxide; D002942:Circular Dichroism; D003577:Cytochrome P-450 Enzyme System; D005290:Ferric Compounds; D005296:Ferrous Compounds; D006415:Hematoporphyrins; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000032:analysis; D006899:Mixed Function Oxygenases; D051381:Rats; D013057:Spectrum Analysis
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D006415:Hematoporphyrins; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D019475:Camphor 5-Monooxygenase