DISCUSSION ON HYDROGEN TRANSPORT 47 



oxidase system and of the action of nitrogen compounds on iron 

 systems. 



The relations of cytochrome oxidase and cytochrome c are such 

 in the oxidation of hydroquinone, for instance, that a decrease of 

 oxidase, which would ordinarily cause a decreased hydroquinone 

 oxidation, could be compensated for by an increase in reduced 

 cytochrome. It has been shown that cyanide does in effect "remove" 

 a certain portion of the oxidase. Hence in a resting tissue, where 

 most of the cytochrome is in the oxidized state, a decreased oxidase 

 could be compensated for by increased reduction of the cytochrome. 

 In the more active state of metabohsm, where there is a small 

 reserve of oxidized cytochrome, such compensation is less possible. 

 The more undissociated the oxidase-inhibitor complex the less eflB- 

 cient would be the compensation. Since azide is a "less powerful" 

 oxidase inhibitor than cyanide, and since the greatest sensitivity to 

 azide is found in the "active" state, these factors may be operative. 



Dr. Ball has considered at some length, in this symposium, the 

 possible differences between cyanide and azide as nitrogenous com- 

 pounds uniting with the oxidase ( Fe) and the lowering of potential 

 caused thereby. He has pictured how a difference in the abihty 

 of the two compounds to unite with the oxidized and reduced forms 

 of the oxidase could lead to differences in the effective potential 

 of the complex formed. Thus the union with cyanide could lead to 

 an oxidase complex with a potential lower than that of cytochrome 

 c, hence possessing a low catalytic power. As a result of combina- 

 tion of higher concentrations of azide with both oxidized and 



o 



reduced oxidase, an effective potential might be reached which could 

 be somewhat higher than that of cytochrome c. Although such a 

 complex would be less eflBcient than the original oxidase, it might 

 nevertheless be suflBcient for the low metabolism that exists in the 

 resting state, although insuflBcient for the metabolism of the "active" 

 tissue. This theory was not advanced to overthrow the "by-pass" 

 theory, but only to call attention to other possible explanations 

 for the differences between azide and cyanide. Perhaps these con- 

 siderations should be exploited before postulating, through the 

 mechanism of as yet unknown enzymes, a "by-pass" around the cyto- 

 chrome system in respiration. 



