Figure 3.

Flash-oxidized cyt c reduction kinetics in wild type, +2Ala, and +1Ala mutants and Q_o site-defective mutant Y147A. The traces obtained with no inhibitor (black), myxothiazol (blue), or stigmatellin (red) with wild type (A), +2Ala mutant (B), +1Ala mutant (C), and Y147A (D) are shown. The ambient redox potential was poised at 100 mV at pH 7.0 such that the Q pool contained substrate QH₂ or at 200 mV for Y147A. Transient kinetics of the flash-induced oxidation and reduction of the cyt c complement were followed at 550–540 nm. The concentrations of myxothiazol and stigmatellin were 5 and 1 μM, respectively, for full inhibition. In C, the traces obtained with myxothiazol at pH 9.0 (light blue), under which conditions a lower [2Fe2S] cluster redox midpoint potential contributes, as expected, to a more prominent reduction of cyt c, are also shown.