5 10 15 20 30 40 50 60 70 80 " IIO 120 130 

 Cytochrome c cone., /^M 



5 10 15 20 30 40 50 60 

 Cytochrome c cone, //M 



Fig. 2. The effect of the concentration of cytochrome c on the velocity constant 

 for the oxidase reaction. 



A. The two curves represent experiments with two different purified oxidase 

 preparations. 



I. The cytochrome c was the Keilin-Hartree preparation; temperature was 

 20^C. The final dilution of the oxidase in the test was 3000-fold. 



II. The cytochrome c was purified according to Margoliash (1954); the tem- 

 perature was 25 C. The final dilution of the oxidase in the test mixture was 

 6000-fold. 



The point represented by D was obtained with a mixture of ferri- and ferro- 

 cytochrome c. The other points were obtained with cytochrome c which was 

 more than 95 % reduced. 



B. Curves III and IV were obtained from experiments with two different heart 

 muscle preparations. 



III. Final dilution of oxidase preparation in test was 1200-fold; temperature 

 was 25°C. 



IV. Final dilution of oxidase in test was 600-fold ; temperature was 20°C. 



