Representative TMRE fluorescence traces in arbitrary units (a.u.) before and after Δψm dissipation with FCCP. Dashed lines indicate where FCCP was added. +/- ATR traces were performed in the absence of succinate. mtON activation was continuous throughout the traces. Light green trace is from mitochondria with ATR, gray traces are without. Quantification of change in fluorescence (ΔF) normalized to the maximum change in fluorescence given by succinate respiration (ΔFmax) for each mitochondrial preparation. Data are from the maximum light dose in Fig. EV 3A. Two-way ANOVA with Sidak's test for multiple comparisons, *p = 0.0469, +ATR succinate vs. +ATR +light p = 0.9978, n = 6 mitochondrial isolations. Data show mean ± SEM. 