Figure 2.

Cytochrome c turnover and superoxide production rate by the bc₁ complex reconstituted in liposomes. (A) Cytochrome c reduction rates are given for a variety of pharmacological manipulations. In the control case, the membrane potential and (2.3 RT/F)ΔpH values were 200 and 15 mV, respectively. With FCCP, both the membrane potential and ΔpH were set to zero. In the nigericin case, the ΔpH was set to 0 mV and the membrane potential was set to 215 mV. When valinomycin was present, the membrane potential was set to 0 mV with the ΔpH unchanged from the control. And when antimycin was present, the Q_n sites were inhibited. (B) Superoxide formation rates for the same pharmacological manipulations for the cytochrome c reduction rate data are shown. (C) The model simulates an exponentially increasing rate of superoxide production as the membrane potential is increased. This is caused by electron retention at the Q_p site of the complex, which leads to higher semiquinone occupancy. Data are from Rottenberg et al. (28). To see this figure in color, go online.