title: Heme-copper and heme-heme interactions in the cytochrome bo-containing quinol oxidase of Escherichia coli.
abstract: The cytochrome bo quinol oxidase of Escherichia coli is one of two respiratory O2 reductases which the bacterium synthesizes. The enzyme complex contains copper and 2 mol of b-type heme. Electron paramagnetic resonance (epr) spectroscopy of membranes from a strain having amplified levels of this enzyme complex reveals signals from low- and high-spin b-type hemes, but the copper, now established as a component of the oxidase, is not directly detectable by epr. The high-spin signal from the cytochrome bo complex, which we attribute to cytochrome o, when titrated potentiometrically, gives a bell-shaped curve. The low potential side of this curve is biphasic (Em7 approximately 180 and 280 mV) and corresponds to the reduction/oxidation of the cytochrome(s). The high potential side of the bell-shaped curve is monophasic (Em7 approximately 370 mV) and is proposed to be due to reduction/oxidation of a copper center which, when in the Cu(II) form, is tightly spin-coupled to a heme, probably cytochrome o, resulting in a net even spin system and loss of the epr spectrum. The low-spin cytochrome b titrates biphasically with Em7 values of approximately 180 and 280 mV, similar to the high-spin component but without the loss of signal at high potentials.
authors.affiliation: Department of Biochemistry and Microbiology, University of St. Andrews, United Kingdom.
authors.forename: J C
authors.initials: JC
authors.lastname: Salerno
authors.forename: B
authors.initials: B
authors.lastname: Bolgiano
authors.forename: R K
authors.initials: RK
authors.lastname: Poole
authors.forename: R B
authors.initials: RB
authors.lastname: Gennis
authors.forename: W J
authors.initials: WJ
authors.lastname: Ingledew
mesh_terms: D002248:Carbon Monoxide / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D003300:Copper / Q000378:metabolism*; D003573:Cytochrome b Group / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006418:Heme / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; D006418:Heme; D003300:Copper; D002248:Carbon Monoxide; C017168:cytochrome bo, E coli; D010088:Oxidoreductases; C020094:duroquinol oxidase