Spectroscopic characterization of the interaction of azide and thiocyanate with the binuclear center of cytochrome oxidase: evidence for multiple ligand sites.
The interactions of azide and thiocyanate with the binuclear center of oxidized cytochrome c oxidase have been characterized by Fourier transform infrared and UV-vis spectroscopy, electron paramagnetic resonance and magnetic and natural circular dichroism. Azide binds in two phases, a high-affinity phase (Kd = 64 microM) in which it is bound as a bridge to the binuclear center and a low-affinity phase (Kd = 20 mM) in which it displaces one of the axial ligands to cytochrome a. Thiocyanate also binds in two phases. The high-affinity phase (Kd = 2.7 mM) involves binding in a terminal mode to CuB; the low-affinity phase is complex and involves both CuA and cytochrome a. In contrast to the recent proposal of Yoshikawa and Caughey [(1990) J. Biol. Chem. 265, 7945-7958], we conclude that cyanide also functions as a bridge between cytochrome a3 and CuB. In the presence of cyanide, azide does not bind to its high-affinity site but thiocyanate does bind to its high-affinity site.
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251-1892.
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D001386:Azides / Q000378:metabolism*; D001665:Binding Sites; D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000378:metabolism*; D005583:Fourier Analysis; D009211:Myoglobin / Q000378:metabolism; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared; D013057:Spectrum Analysis; D013482:Superoxide Dismutase / Q000378:metabolism; D013861:Thiocyanates / Q000378:metabolism*
D001386:Azides; D003574:Cytochrome c Group; D009211:Myoglobin; D013861:Thiocyanates; D013482:Superoxide Dismutase; D003576:Electron Transport Complex IV; C031760:thiocyanate