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 μM. 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 K(d) of 30 μM 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 k(on) = 600 M-1 s-1. Decay of the H2O2-induced spectral changes upon addition of catalase (k ~ 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 K(d) and k(on) values given above (k(off) = K(d)(*)k(on)). 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.
|Original language||English (US)|
|Number of pages||8|
|Journal||Biochemistry and Molecular Biology International|
|State||Published - 1995|
ASJC Scopus subject areas
- Molecular Biology