title: Kinetic trapping of oxygen in cell respiration.
abstract: Cell respiration in eukaryotes is catalysed by mitochondrial enzyme cytochrome c oxidase. In bacteria there are many variants of this enzyme, all of which have a binuclear haem iron-copper centre at which O2 reduction occurs, and a low-spin haem, which serves as the immediate electron donor to this centre. It is essential that the components of the cell respiratory system have a high affinity for oxygen because of the low concentration of dissolved O2 in the tissues; however, the binding of O2 to the respiratory haem-copper oxidases is very weak. This paradox has been attributed to kinetic trapping during fast reaction of O2 bound within the enzyme's binuclear haem iron-copper centre. Our earlier work indicated that electron transfer from the low-spin haem to the oxygen-bound nuclear centre may be necessary for such kinetic oxygen trapping. Here we show that specific decrease of the haem-haem electron transfer rate in the respiratory haem-copper oxidase from Escherichia coli leads to a corresponding decrease in the enzyme's operational steady-state affinity for O2. This demonstrates directly that fast electron transfer between the haem groups is a key process in achieving the high affinity for oxygen in cell respiration.
authors.affiliation: Helsinki Bioenergetics Group, Department of Medical Chemistry, Institute of Biomedical Sciences, Finland.
authors.forename: M I
authors.initials: MI
authors.lastname: Verkhovsky
authors.forename: J E
authors.initials: JE
authors.lastname: Morgan
authors.forename: A
authors.initials: A
authors.lastname: Puustein
authors.forename: M
authors.initials: M
authors.lastname: Wikström
mesh_terms: D003573:Cytochrome b Group; D003580:Cytochromes / Q000378:metabolism; D004579:Electron Transport; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins; D006418:Heme / Q000378:metabolism*; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism*
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; C083850:cytochrome bo3, E coli; C083851:cytochrome oo3, E coli; D006418:Heme; D010100:Oxygen