The rate-limiting step in O 2 reduction by cytochrome ba 3 from Thermus thermophilus

Tsuyoshi Egawa, Ying Chen, James A. Fee, Syun Ru Yeh, Denis L. Rousseau

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Cytochrome ba 3 (ba 3) of Thermus thermophilus (T. thermophilus) is a member of the heme-copper oxidase family, which has a binuclear catalytic center comprised of a heme (heme a 3) and a copper (Cu B). The heme-copper oxidases generally catalyze the four electron reduction of molecular oxygen in a sequence involving several intermediates. We have investigated the reaction of the fully reduced ba 3 with O 2 using stopped-flow techniques. Transient visible absorption spectra indicated that a fraction of the enzyme decayed to the oxidized state within the dead time (~ 1 ms) of the stopped-flow instrument, while the remaining amount was in a reduced state that decayed slowly (k = 400 s - 1) to the oxidized state without accumulation of detectable intermediates. Furthermore, no accumulation of intermediate species at 1 ms was detected in time resolved resonance Raman measurements of the reaction. These findings suggest that O 2 binds rapidly to heme a 3 in one fraction of the enzyme and progresses to the oxidized state. In the other fraction of the enzyme, O 2 binds transiently to a trap, likely Cu B, prior to its migration to heme a 3 for the oxidative reaction, highlighting the critical role of Cu B in regulating the oxygen reaction kinetics in the oxidase superfamily. This article is part of a Special Issue entitled: Respiratory Oxidases.

Original languageEnglish (US)
Pages (from-to)666-671
Number of pages6
JournalBiochimica et Biophysica Acta - Bioenergetics
Issue number4
StatePublished - Apr 2012
Externally publishedYes


  • Bioenergetics
  • Cytochrome oxidase
  • Raman scattering
  • Stopped-flow

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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