The effect of pH changes on the optical spectrum of oxidised cytochrome oxidase.
The sensitivity to pH changes of oxidised cytochrome oxidase, oxidised oxidase-cyanide and oxidase-azide complexes was investigated by optical difference spectroscopy in the pH region 6.0-8.2. The responses of the optical spectrum of oxidised oxidase and the oxidase-cyanide complex are almost fully developed within some minutes after a pH change of 1-2 units. A blue shift of the spectrum of oxidised oxidase and the oxidase-cyanide complex is observed with decreasing pH, whereas the oxidase-azide complex is almost insensitive to the pH change. From the pH insensitivity of the oxidase-azide complex and the differences in the pH-induced spectral changes of the oxidase-cyanide complex relative to unliganded oxidase, it is concluded that the spectral pH sensitivity in the oxidised enzyme is probably associated with proton binding at or near cytochrome a3 only. Similar absorption changes are observed with the oxidised oxidase on increasing the pH and on the binding of azide to oxidised oxidase at constant pH. It is suggested that azide binding is probably associated with the deprotonation of some ionizable group(s) in the vicinity of the cytochrome a3-CuB site.
Fabian
M
M
Department of Biochemistry and Biophysics, Chalmers University of Technology, Göteborg, Sweden.
Malmström
B G
BG
D000818:Animals; D001386:Azides; D002417:Cattle; D003576:Electron Transport Complex IV; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D011190:Potassium Cyanide; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet
D001386:Azides; D003576:Electron Transport Complex IV; D011190:Potassium Cyanide