Composition of Cytochrome c Oxidase 



295 



D. Reactions with Cyanide 



Warburg's (1924) theory of the role of iron in biological oxidations was 

 founded largely on the inhibitory effect of cyanide on respiration. Warburg 

 (1927) later concluded that cyanide combines with the oxidized form of the 

 enzyme. He found that the degree of inhibition by cyanide was independent 



*.IQ0 



- 



-.100 



350 



400 



450 300 550 

 Wave Length (mfi) 



600 



650 



Fig. 3. Effect of cyanide on the spectrum of oxidized cytochrome c oxidase. 



of the oxygen tension and therefore cyanide and oxygen were not competing 

 for the reduced form of the enzyme. The inhibition was amply confirmed by 

 Keilin and Hartree (1939), who used the partial effect of cyanide on the 

 spectrum of the reduced enzyme as support for their concept that there are two 

 cytochromes a. 



The effects of cyanide on the spectra of both the oxidized and reduced 

 forms of the soluble enzyme (Wainio, 1955c) may be seen in Figs. 3 and 4 

 (see also Smith, 1951; Ball and Cooper, 1952; Lundegardh, 1953). It is 

 first to be noted that the effects are much more pronounced with the reduced 

 enzyme than with the oxidized enzyme. This would suggest that it is the 

 reduced form of the enzyme that is cyanide-sensitive. Furthermore, a study 

 of the oxidized curves suggests that cyanide, which is a reducing agent, has 



