title: Potentiometric titration of cytochrome-bo type quinol oxidase of Escherichia coli: evidence for heme-heme and copper-heme interaction.
abstract: The cytochrome-bo quinol oxidase of Escherichia coli contains a high-spin b-type heme (cytochrome o), a low-spin b-type heme (cytochrome b) and copper. The EPR signal from cytochrome o is axial high spin and when titrated potentiometrically gives a bell-shaped curve. The low-potential side of this curve (Em7 approx. 160 mV) corresponds to the reduction/oxidation of the cytochrome. The high-potential side (Em7 approx. 350 mV) is proposed to be due to reduction/oxidation of a copper center; in the CuII form tight cytochrome o-copper spin coupling results in a net even spin system and loss of the EPR spectrum. Optical spectra of the alpha-bands of the reduced cytochromes at 77 K show that cytochrome b has its maxima at 564 nm when cytochrome o is oxidized but that this shifts to 561 nm when cytochrome o (max. 555 nm) is reduced. Both a heme-copper (cytochrome o-CuII) and a heme-heme (cytochrome o-cytochrome b) interaction are indicated in this quinol oxidase. These results indicate that cytochrome-bo quinol oxidase has a binuclear heme-copper catalytic site and suggest striking structural similarity to subunit I of the cytochrome aa3 system.
authors.affiliation: Department of Biochemistry and Microbiology, University of St. Andrews, Scotland.
authors.forename: J C
authors.initials: JC
authors.lastname: Salerno
authors.forename: B
authors.initials: B
authors.lastname: Bolgiano
authors.forename: W J
authors.initials: WJ
authors.lastname: Ingledew
mesh_terms: D003300:Copper / Q000378:metabolism*; D003573:Cytochrome b Group / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology*; D006418:Heme / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D011199:Potentiometry; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D006418:Heme; D003300:Copper; D010088:Oxidoreductases; C020094:duroquinol oxidase