FIGURE 6.

Contribution of site III_Qo at “rest.” Mitochondria were incubated in medium mimicking rest (Table 1). A, rate of superoxide production from site III_Qo, defined as the rate in the presence of 4 μm rotenone sensitive to 4 μm myxothiazol, at different ratios of succinate/malonate (total concentration 5 mm). Data were corrected for changes in the contribution of site I_F using changes in the NAD(P)H redox state and the calibration curve in Fig. 5C (Table 3) (24). B, dependence of cytochrome b₅₆₆ reduction state on the succinate/malonate ratio under the same conditions (100% reduction was established by adding 5 mm succinate plus 2 μm antimycin A). C, calibration curve obtained by combining the y axes from A and B showing the dependence of the rate of superoxide produced from site III_Qo on the cytochrome b₅₆₆ reduction level. D, total rate of H₂O₂ production at “rest” (from Fig. 2D) and the contributions of sites I_F (from Fig. 5D) and III_Qo (assessed from the reduction state of cytochrome b₅₆₆ in Fig. 4 and the calibration curve in C). Inverted error bars indicate the propagated errors for each site, and the conventional error bar indicates the propagated sum of these errors. Values are means ± S.E. (error bars) (n = 3–20). p < 0.0001 by Welch's t test.