Figure 8. Effect of mitoQ and TPP compounds on the respiration of rat liver mitochondria.

(A and B) Double logarithmic plots of uncoupling in the presence (squares) and absence (circles) of 2 nmol of CAT/mg of protein (added before succinate). Open symbols, titration of respiration rate with (A) mitoQ₁₀ or (B) decylTPP. In the presence of CAT, concentrations of mitoQ₁₀ or decylTPP below 10⁻⁷ M gave a less than 1% increase in respiration and are off-scale. Closed symbols, rate at each mitoQ₁₀ or decylTPP concentration after subsequent addition of 0.3 μM FCCP. Values are means±S.E.M. for three to four independent experiments. Lines (no CAT, dashed line; with CAT, dotted line) were fitted to the points shown by regression. (C and D) Comparison of uncoupling by a series of (C) mitoQ compounds and (D) TPP cations with different numbers of carbon atoms (from three to ten) in the alkyl chain (grey bars). The concentration used for this comparison was 10⁻⁹ M. At this concentration, CAT inhibited any uncoupling effect by these compounds (black bars). Data with mitoBHT (Figures 7C and 7D) and TPMP (MethylTPP; Figure 7C) are included for comparison.