INTERMEDIARY OXIDATION REACTION BETWEEN THE TWO REDUCTION PHASES DURING THE TRIPHASIC COURSE OF CYTOCHROME b REDUCTION

The reduction of eytochrome b in the succinate-cytoehrome c reduetase by either succinate or duroquinol follows a triphasic course in the pH range 6.0—9.0. The rates of all the three phases of cytochrome b oxldation-reduction as well as the rate of reduction of cytochrome c increase with increasing pH. The course of both the triphasic changes and the multiphasic oxidation-reduction changes of cytochrome b in the presence of added cytochrome c have also been followed by repeated spectral scan at 4℃. In all cases, the reduction and oxidation of cytochrome b are clearly indicated by the appearance and disappearance of the 562 nm peak in the reduced minus oxidized spectra. The accumulation of ubisemiquinone at center i has been suggested to be responsible for the oxidation phase of cytochrome b.