172 A SYMPOSIUM ON RESPIRATORY ENZYMES 



of the available reducing systems. With a given lower potential of 

 the oxidase-inhibitor complex, the lower the potential of the reduc- 

 ing system the less sensitive would be the respiration to the inhibitor. 

 On this basis, a system in which cytochrome c (with a relatively high 

 potential) is the normal reducing agent of the oxidase would be 

 expected to show a high sensitivity to oxidase inhibitors. In the 

 absence of cytochrome c this theory provides an explanation of 

 cyanide or azide stability even when the cyanide may be combining 

 with the oxidase component. Such a theory deserves consideration 

 in the interpretation of all experiments purporting to demonstrate 

 the "by-passing" or non-functioning of the cytochrome-cytochrome 

 oxidase system. 



The frontiers of research in the cytochrome problem therefore ap- 

 pear to consist on the biochemical side in the isolation and proper- 

 ties of the individual components, and on the physiological side in 

 the mode of function or non-function of this system in various states 

 of metabolism of tissues. 



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