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Time-Resolved Step-Scan Fourier Transform Infrared Spectroscopy of the CO Adducts of Bovine Cytochrome c Oxidase and of Cytochrome bo 3 from Escherichia coli

2002; American Chemical Society; Volume: 41; Issue: 8 Linguagem: Inglês

10.1021/bi010823g

1943-295X

James A. Bailey, Farol L. Tomson, Sandra L. Mecklenburg, Gina MacDonald, Andromachi Katsonouri, Anne Puustinen, Robert B. Gennis, William H. Woodruff, R. Brian Dyer,

Photoreceptor and optogenetics research

We have used cryogenic difference FTIR and time-resolved step-scan Fourier transform infrared (TR-FTIR) spectroscopies to explore the redox-linked proton-pumping mechanism of heme−copper respiratory oxidases. These techniques are used to probe the structure and dynamics of the heme a3−CuB binuclear center and the coupled protein structures in response to the photodissociation of CO from heme Fe and its subsequent binding to and dissociation from CuB. Previous cryogenic (80 K) FTIR CO photodissociation difference results were obtained for cytochrome bo3, the ubiquinol oxidase of Escherichia coli [Puustinen, A., et al. (1997) Biochemistry 36, 13195−13200]. These data revealed a connectivity between CuB and glutamic acid E286, a residue which has been implicated in proton pumping. In the current work, the same phenomenon is observed using the CO adduct of bovine cytochrome aa3 under cryogenic conditions, showing a perturbation of the equivalent residue (E242) to that in bo3. Furthermore, using time-resolved (5 μs resolution) step-scan FTIR spectroscopy at room temperature, we observe the same spectroscopic perturbation in both cytochromes aa3 and bo3. In addition, we observe evidence for perturbation of a second carboxylic acid side chain, at higher frequency in both enzymes at room temperature. The high-frequency feature does not appear in the cryogenic difference spectra, indicating that the perturbation is an activated process. We postulate that the high-frequency IR feature is due to the perturbation of E62 (E89 in bo3), a residue near the opening of the proton K-channel and required for enzyme function. The implications of these results with respect to the proton-pumping mechanism are discussed. Finally, a fast loss of over 60% of the CuB−CO signal in bo3 is observed and ascribed to one or more additional conformations of the enzyme. This fast conformer is proposed to account for the uninhibited reaction with O2 in flow−flash experiments.