Oxygen-linked equilibrium CuB-CO species in cytochrome ba3 oxidase from Thermus thermophilus: Implications for an oxygen channel at the CuB site

Konstantinos Koutsoupakis, Stavros Stavrakis, Tewfik Soulimane, Constantinos Varotsis

Research output: Contribution to journalArticlepeer-review

Abstract

We report the first study of O2 migration in the putative O2 channel of cytochrome ba3 and its effect to the properties of the binuclear heme a3-CuB center of cytochrome ba3 from Thermus thermophilus. The Fourier transform infrared spectra of the ba3-CO complex demonstrate that in the presence of 60-80 μM O2, the ν(C-O) of CuB1+-C-O at 2053 cm-1 (complex A) shifts to 2045 cm-1 and remains unchanged in H2O/D2O exchanges and in the pH 6.5-9.0 range. The frequencies but not the intensities of the C-O stretching modes of heme a3-CO (complex B), however, remain unchanged. The change in the ν(C-O) of complex A results in an increase of k-2, and thus in a higher affinity of CuB for exogenous ligands. The time-resolved step-scan Fourier transform infrared difference spectra indicate that the rate of decay of the transient CuB1+-CO complex at pH 6.5 is 30.4 s-1 and 28.3 s-1 in the presence of O2. Similarly, the rebinding to heme a3 is slightly affected and occurs with k2 = 26.3 s-1 and 24.6 s-1 in the presence of O2. These results provide solid evidence that in cytochrome ba3, the ligand delivery channel is located at the CuB site, which is the ligand entry to the heme a3 pocket. We suggest that the properties of the O2 channel are not limited to facilitating ligand diffusion to the active site but are extended in controlling the dynamics and reactivity of the reactions of ba3 with O2 and NO.

Original languageEnglish
Pages (from-to)14893-14896
Number of pages4
JournalJournal of Biological Chemistry
Volume278
Issue number17
DOIs
Publication statusPublished - 25 Apr 2003
Externally publishedYes

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