CYTOCHROMES 



165 



c and h. This preparation was essentially unable to oxidize either 

 hydroquinone or p-phenylenediamine without the addition of cyto- 

 chrome c. 



A study of the cyanide sensitivity of hydroquinone and 

 p-phenylenediamine oxidation (see Table 1) suggested, because of 

 the redox potential relations of the cytochromes and the substrates, 

 that hydroquinone oxidation involved only the oxidase and cyto- 

 chrome c, whereas p-phenylenediamine could be independently 

 oxidized by cytochrome h as well. The cyanide-resistant portion of 

 p-phenylenediamine oxidation is probably due to the autoxidizable, 

 cyanide-resistant cytochrome h. 



The oxidation of hydroquinone is a function of both the oxidase 

 and cytochrome c; hence its oxidation by tissue extracts is not an 

 absolute method for determining either substance. The effect of 

 cytochrome c in accelerating the rate of hydroquinone oxidation by 

 a heart muscle oxidase preparation is shown in Figure 3. 



500 



400 



300 



200 



100 



Velocity 

 (cmm. 02/hr.) 



h ) i S^ o 



-^Mr 



O addition of cytochrome clone 



A oddition of cytochrome to heated oxidase 



■ addition of cytochrome to crude oxidase preparation 



I I I I I I I I 1 



10 20 30 40 50 60 70 80 



Added cytochrome c (mM. X|0^) 



90 100 



Figure 3. — The oxidation of hydroquinone by the oxidase-cytochrome c system. 

 T = 38°C., pH 7.15, hydroquinone 0.033 mM. total. 



