On the Redox Potentials of Ubiquinone and Cytochrome <em>b</em> in the Respiratory Chain.

The standard redox potential of ubiquinone in submitochondrial particles is measured by equilibration with the succinate/fumarate system to about 65 mV at pH 7, with the redox ration, n = 2. The pH dependence is -60 mV/ΔpH. The lower value measured for bound ubiquinone is discussed in comparison with the value found for isolated ubiquinone (104 to 112 mV, pH 7) determined in ethanol - HCl. In parallel experiments the standards redox potential of cytochrome b was measured to 72.5 mV at pH 7. The pH dependence is ΔE/ΔpH = 0 at pH < 6.8 and -60 mV ΔHp at pH > 6.8 [ABSTRACT FROM AUTHOR]