Fig. 8. Respiration of gill mitochondria from sulfide-free mussels with sequential inhibition of terminal oxidases. (A,B) Traces of oxygen partial pressure P_O2 (black line) and sulfide concentration (red line) over time. Sulfide additions at 6.25 µmol l^–1 (a), 12.5 µmol l^–1 (b) and 18.75 µmol l^–1 (c) were repeated under non-limiting oxygen conditions and in the presence 1 mmol l^–1 potassium cyanide (KCN) and 1 mmol l^–1 salicylhydroxamic acid (SHAM) to inhibit cytochrome c oxidase and the alternative oxidase, respectively. (C) Derivatives of oxygen (black line) and sulfide (red line) traces showing consumption rates (_O2 and _H2S, respectively). Rates are lower than those from sulfide-maintained mussels (Fig. 7) but remain coupled, although limits are reached at all sulfide concentrations. (D) KCN-inhibition of cytochrome c oxidase and then alternative oxidase with SHAM results in further decreases in both oxygen and sulfide consumption rates, however the two events remain coupled. Note the compressed time scale in B and D.