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Role of a bound ubiquinone on reactions of theEscherichia colicytochromebowith ubiquinol and dioxygen11 This is paper XXXIII in the series ‘Structure-function studies on the E. coli cytochrome bo’.

Authors
Journal
FEBS Letters
0014-5793
Publisher
Wiley Blackwell (John Wiley & Sons)
Publication Date
Volume
457
Issue
2
Identifiers
DOI: 10.1016/s0014-5793(99)01047-9
Keywords
  • Bound Quinone
  • Cytochromebo
  • Quinol Oxidase
  • Time-Resolved Visible Spectroscopy
  • Escherichia Coli
Disciplines
  • Biology

Abstract

Abstract To probe the functional role of a bound ubiquinone-8 in cytochrome bo-type ubiquinol oxidase from Escherichia coli, we examined reactions with ubiquinol-1 and dioxygen. Stopped-flow studies showed that anaerobic reduction of the wild-type and the bound ubiquinone-free (ΔUbiA) enzymes with ubiquinol-1 immediately takes place with four kinetic phases. Replacement of the bound ubiquinone with 2,6-dibromo-4-cyanophenol (PC32) suppressed the anaerobic reduction of the hemes with ubiquinol-1 by eliminating the fast phase. Flow-flash studies in the reaction of the fully reduced enzyme with dioxygen showed that the heme b-to-heme o electron transfer occurs with a rate constant of ∼1×10 4 s −1 in all three preparations. These results support our previous proposal that the bound ubiquinone is involved in facile oxidation of substrates in subunit II and subsequent intramolecular electron transfer to low-spin heme b in subunit I.

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