Figure 4.

Concentration dependence of succinate-induced inhibition of H₂O₂ production by complex II-inhibited mitochondria. A, mitochondria (Mito) were incubated with AA5 (1 μm) and succinate (Succ) at the concentrations indicated at the end of trace. After permeabilization with alamethicin (Ala), H₂O₂ production was lower at higher [succinate]. The initial rate of H₂O₂ production with 10 μm succinate present (red trace) was similar to that generated by endogenous substrates in the absence of added succinate (purple trace). As in other figures, additions to all traces are indicated by black arrows; additions to one trace only are indicated by the arrows of the same color as the trace. B, H₂O₂ production in AA5 (0.5 μm)-inhibited mitochondria initiated by alamethicin was progressively suppressed by adding exogenous succinate in increasing concentrations, as indicated at the end of traces. At the end H₂O₂ production was inhibited with malonate (Malon) (5 mm). C, summary data for inhibition of H₂O₂ production as a function the [succinate], showing half-maximal inhibition at 297 μm. Shaded areas indicate 95% confidence intervals. Ant, antimycin; Stigm, stigmatellin.