title: EPR studies of the cytochrome-d complex of Escherichia coli.
abstract: We have examined the thermodynamic and EPR properties of one of the ubiquinol oxidase systems (the cytochrome d complex) of Escherichia coli, and have assigned the EPR-detectable signals to the optically identified cytochromes. The axial high spin g = 6.0 signal has been assigned to cytochrome d based on the physicochemical properties of this signal and those of the optically defined cytochrome d. A rhombic low spin species at gx,y,z = 1.85, 2.3, 2.5 exhibited similar properties but was present at only one-fifth the concentration of the axial high spin species. Both species have an Em7 of 260 mV and follow a -60 mV/pH unit dependence from pH 6 to 10. The rhombic high spin signal with gy,z = 5.5 and 6.3 has been assigned to cytochrome b-595. This component has an Em7 of 136 mV and follows a -30 mV/pH unit dependence from pH 6 to 10. Lastly, the low spin gz = 3.3 signal which titrates with an Em7 of 195 mV and follows a -40 mV/pH unit dependence from pH 6 to 10 has been assigned to cytochrome b-558. Spin quantitation of the high-spin signals indicates that cytochrome d and b-595 are present in approximately equal amounts. These observations are discussed in terms of the stoichiometry of the prosthetic groups and its implications on the mechanism of electron transport.
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104.
authors.forename: S W
authors.initials: SW
authors.lastname: Meinhardt
authors.forename: R B
authors.initials: RB
authors.lastname: Gennis
authors.forename: T
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D003573:Cytochrome b Group / Q000378:metabolism; D017937:Cytochrome d Group; D003580:Cytochromes / Q000302:isolation & purification / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D045222:Electron Transport Chain Complex Proteins; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D007700:Kinetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D017937:Cytochrome d Group; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli