FIGURE 6.

Comparison of NADH- and RET-induced H₂O₂ production by complex I in SMPs. The two curves have been normalized independently. Black, NADH-induced H₂O₂ production by complex I in SMPs inhibited by rotenone with Δp ∼ 0.16 V (from Fig. 3). Red, RET induced H₂O₂ production by complex I in SMPs inhibited by KCN. The RET data are plotted using E_Set = −0.020 V −RT/2F. In{[succinate]/[fumarate]} + 2.Δp (10 mm succinate, variable fumarate concentrations) and fit by the Nernst equation for a 2-electron cofactor with two distinct potentials described by their average value, E_av = −0.305 V, and their separation, ΔE = −0.020 V. The rotenone independent rates (see Fig. 5) have been subtracted. The asterisk marks the 0.024 V increase in Δp (measured at E_1/2) that is required to overlay the RET-induced data on the NADH-induced data. See “Experimental Procedures” for conditions.