Kinetic parameters of cytochrome c oxidase in rat skeletal muscle: effect of endurance training.

The kinetic properties of cytochrome c oxidase (EC 1.9.3.1) in skeletal muscle tissue of sedentary and endurance-trained rats were studied. The initial velocity of the cytochrome c oxidase reaction was determined polarographically over a large range of cytochrome c concentrations and the maximal velocity (Vmax) and the Michaelis constant (Km) were calculated. The catalytic activity of cytochrome c oxidase in isolated mitochondria was also investigated. The training programme consisted of treadmill running for 2 h a day, 6 days a week, at a speed of 30 m min-1 and 30 degrees elevation, for 4 weeks. Vmax of cytochrome oxidase with respect to cytochrome c increased significantly from 254 to 310 mumol O2 min-1 g-1 protein in response to training (P less than 0.001), whereas Km remained unchanged (18.9 and 18.7 microM). The turnover number (TN) increased from 11.1 S-1 in sedentary rats to 16.6 S-1 in trained rats (P less than 0.001). The results suggest a qualitative change in the enzyme molecule in addition to a true Vmax change of cytochrome c oxidase in response to endurance training.