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Oxoferryl-Porphyrin Radical Catalytic Intermediate in Cytochrome bd Oxidases Protects Cells from Formation of Reactive Oxygen Species.
- Source :
-
Journal of Biological Chemistry . 3/16/2012, Vol. 287 Issue 12, p8830-8838. 9p. - Publication Year :
- 2012
-
Abstract
- The quinol-linked cytochrome bd oxidases are terminal oxidases in respiration. These oxidases harbor a low spin heme b558 that donates electrons to a binuclear heme b595/heme d center. The reaction with O2 and subsequent catalytic steps of the Escherichia coli cytochrome bd-I oxidase were investigated by means of ultra-fast freeze-quench trapping followed by EPR and UV-visible spectroscopy. After the initial binding of O2, the O-O bond is heterolytically cleaved to yield a kinetically competent heme d oxoferryl porphyrin π-cation radical intermediate (compound I) magnetically interacting with heme b595. Compound I accumulates to 0.75-0.85 per enzyme in agreement with its much higher rate of formation (∼20,000 s-1) compared with its rate of decay (∼1,900 s-1). Compound I is next converted to a short lived heme d oxoferryl intermediate (compound II) in a phase kinetically matched to the oxidation of heme b558 before completion of the reaction. The results indicate that cytochrome bd oxidases like the heme-copper oxidases break the O-O bond in a single four-electron transfer without a peroxide intermediate. However, in cytochrome bd oxidases, the fourth electron is donated by the porphyrin moiety rather than by a nearby amino acid. The production of reactive oxygen species by the cytochrome bd oxidase was below the detection level of 1 per 1000 turnovers. We propose that the two classes of terminal oxidases have mechanistically converged to enzymes in which the O-O bond is broken in a single four-electron transfer reaction to safeguard the cell from the formation of reactive oxygen species. [ABSTRACT FROM AUTHOR]
- Subjects :
- *ESCHERICHIA coli
*CYTOCHROMES
*OXIDASES
*HEME
*OXIDATION-reduction reaction
Subjects
Details
- Language :
- English
- ISSN :
- 00219258
- Volume :
- 287
- Issue :
- 12
- Database :
- Academic Search Index
- Journal :
- Journal of Biological Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 76115030
- Full Text :
- https://doi.org/10.1074/jbc.M111.333542