164 A SYMPOSIUM ON RESPIRATORY ENZYMES 



dizable and that it does not react with cytochrome c but only with 

 "carriers" such as methylene blue. It is not yet known whether this 

 protein requires another link (such as cytochrome h) for cytochrome 

 c reduction, or whether it is actually a denatured product which 

 has lost its ability to reduce cytochrome c, analogous to the old 

 Warburg-Christian yellow enzyme and the newer cytochrome re- 

 ductase. 



Catalytic Relations of the Cytochromes and Oxidase 



"Indophenol oxidase" was long recognized as the substance in 

 tissues which produced the aerobic oxidation of Nadi reagent or 

 p-phenylenediamine (3). This name was retained in spite of the 

 finding of Keilin (71) that the addition of cytochrome c accelerated 

 the oxidation of cysteine by "indophenol oxidase" and a similar 

 finding by Stotz, Harrer, Schultze, and King (72) with respect to 

 ascorbic acid. When pure cytochrome c became available, it was 

 not difficult to study the relation of oxidase and cytochrome c in 

 the oxidation of various substrates. The high oxidation-reduction 

 potential of cytochrome c that had been noted suggested that the 

 action of indophenol oxidase was due to an unspecific reduction of 

 the cytochrome c which it contained, followed by an aerobic cata- 

 lyzed oxidation of the reduced cytochrome. KeiHn and Hartree (73), 

 upon noting the accelerating efi^ect of cytochrome c on the oxidation 

 of several substrates, renamed the oxidase "cytochrome oxidase." 

 Stotz, Sidwell, and Hogness (74) had come to the same conclusion 

 and had prepared an oxidase which was largely free of cytochromes 



Table 1.— The sensitivity of hydroquinone and p-phenylenediamine 

 oxidations to cyanide* 



(Reference 74) 



T = 38° C; pH, 7.15; 23.5 X 10"* mM cytochrome c total. 



