Fig. 2. Oxygen pressure in a suspension of mitochondria reported polarographically as a function of time (1 torr=0.133 kPa). ADP (500 nmol) is added at the arrows. A, myoglobin absent; B, 500 µmol l^–1 oxymyoglobin. Average oxygen uptake in the presence of adequate ADP is 193 and 157 mol O₂ (mol cytochrome aa₃)^–1 min^–1 in the absence and presence of myoglobin, respectively. P/O ratios are 2.21 and 2.20. The concentration of myoglobin used here exceeds the volume-average concentration in pigeon heart, 209 µmol l^–1 (Schuder et al., 1979). These results show that myoglobin in the solution does not affect the respiratory parameters of isolated mitochondria.