Fig. 7. Respiration of gill mitochondria from sulfide-maintained 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 of 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. Sulfide consumption rate (_H2S) proportionally increases while oxygen consumption rate (_O2) reaches a limit and is inhibited at the highest sulfide concentration. (D) KCN-inhibition of cytochrome c oxidase results in truncated and unmatched rates of oxygen and sulfide consumption. SHAM-inhibition of alternative oxidase results in complete oxygen consumption inhibition while sulfide consumption continues at a low level. Note the compressed time scale in B and D.