title: Kinetics of the reactions of trioxodinitrate and nitrite ions with cytochrome d in Escherichia coli.
abstract: The rate of reaction of trioxodinitrate with reduced cytochrome oxidase d in membrane particles from Escherichia coli at pH 7 and 25 degrees C depends linearly upon [HN2O3-] over the concentration range studied (up to 0.05 mM) and is also first-order in cytochrome d. The known rate of decomposition of trioxodinitrate to give NO- and NO2- is about 4.5-times faster than the rate of reaction of reduced cytochrome d with trioxodinitrate, implying that cytochrome d reacts directly with NO-, with a trapping ratio of between 0.20 and 0.25, rather than with trioxodinitrate. The implications of the facile formation of the NO(-)-nitrosyl complex of cytochrome d for the mechanism of denitrification are discussed with particular reference to the mechanism of N-N bond formation. The reaction of reduced cytochrome d with nitrite (a decomposition product of trioxodinitrate) under these conditions is much slower than that with trioxodinitrate. The kinetics show a biphasic dependence of initial rate upon nitrite concentration. The rate data at low [NO2-] are consistent with saturation of a high affinity site for nitrite, having Vmax = 4.29.10(-9) M s-1 and Km = 0.034 mM. The existence of two binding sites for nitrite is consistent with the suggestion that the cytochrome bd complex contains two cytochrome d haems.
authors.affiliation: Department of Chemistry, King's College London, U.K.
authors.forename: F T
authors.initials: FT
authors.lastname: Bonner
authors.forename: M N
authors.initials: MN
authors.lastname: Hughes
authors.forename: R K
authors.initials: RK
authors.lastname: Poole
authors.forename: R I
authors.initials: RI
authors.lastname: Scott
mesh_terms: D017937:Cytochrome d Group; D003580:Cytochromes / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D013053:Spectrophotometry; D013379:Substrate Specificity
chemical_list: D003580:Cytochromes; D009566:Nitrates; D009573:Nitrites; C067288:trioxodinitrate; D017937:Cytochrome d Group