title: Peroxide complex of cytochrome bd: kinetics of generation and stability.
abstract: Hydrogen peroxide reacts with the isolated fully oxidized cytochrome bd from Escherichia coli bringing about spectral changes characterized by increased absorption at 680 nm, disappearance of a charge transfer band at 740 nm and a red shift in the Soret band. Only one type of spectral changes is observed throughout the entire range of H2O2 concentration studied, 5 - 5000 microM. The absorption changes are consistent with peroxide binding to heme d and do not show any evidence for reaction with heme b-595. The spectral response saturates at increased H2O2 concentration with apparent Kd of 30 microM and is reversed by catalase. Stopped-flow measurements show the reaction to be first order with respect to H2O2 with a second order rate constant Kon = 600M-1s-1. Decay of the H2O2-induced spectral changes upon addition of catalase (k approximately 0.001 s-1) is about 20-fold slower than expected for dissociation of peroxide from the complex with heme d assuming a simple reversible binding of H2O2 with Kd and Kon values give above (Koff = Kon). We suggest that the reaction of H2O2 with cytochrome bd may be in fact irreversible, the initial binding followed by a cleavage of the O-O bond and formation of the oxoferryl complex of heme d. Upon removal of excess peroxide, the oxoferryl compound could decay being reduced to the ferric state by endogenous reductants.
authors.affiliation: A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
authors.forename: V
authors.initials: V
authors.lastname: Borisov
authors.forename: R
authors.initials: R
authors.lastname: Gennis
authors.forename: A A
authors.initials: AA
authors.lastname: Konstantinov
mesh_terms: D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry*; D045222:Electron Transport Chain Complex Proteins; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D006861:Hydrogen Peroxide; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli