Fig. 9. Sulfide-stimulated oxygen and sulfide consumption rates of mussel gill mitochondria as a function of oxygen partial pressure. Three experiments (differentiated by symbols) of repeated (5–8) additions of 10–13 µmol l^–1 sulfide, as shown in Fig. 6, demonstrate a conformity of oxygen (black symbols) and sulfide (red symbols) consumption rates as P_O2 declines. The rate of oxygen consumption shows limitation at higher P_O2 with an apparent P₅₀ near 2 kPa whereas the apparent P₅₀ for sulfide consumption is approximately 1 kPa; data fitted by Michaelis–Menten equation.