108 



Britton Chance 



the other components (Martins, 1956), we have endeavoured 

 to learn whether dicoumarol concentrations which cause loss 

 of respiratory control equally affect the respiratory carriers. 

 We have, therefore, carried out a dicoumarol titration of the 

 steady-state oxidation-reduction level of cytochrome c (Fig. 

 13) in the presence of azide to increase the spectroscopic 

 effects. The same dicoumarol concentration (4 (xm) is required 



30-1 



o 



3 '— 



a» ♦- 



a: s 



O 



O ♦- 



o < 



20" 



10 



Titration of State 4-3 transition. 

 200;iM Azide 

 10®. Succinale as substrate 



-r— 

 10 



[Dicoumarol] (>jM) 



Fig. 13. Titration of the steady state oxidation-reduction level of cytochrome 

 c with the uncoupling agent, dicoumarol. Mitochondria pretreated with azide, 

 succinate as substrate. Increasing cytochrome reduction is caused by increas- 

 ing dicoumarol concentration. (Expt. no. 529) 



for half-maximal interaction with the cytochrome c compon- 

 ent as is required for half-maximal activation of respiration. 

 There are, however, slight differences in the experimental 

 conditions that might make this close agreement fortuitous: 

 the data of Fig. 13 were obtained at lower temperatures and 

 with succinate as substrate. Nevertheless, we can find no 

 significant discrepancy between the response of the carriers 

 and the response of the whole chain to dicoumarol that would 

 lead us to believe that one site of phosphorylation can be 

 uncoupled independently of the others by dicoumarol. 

 Further evidence for the similarity of the site specificity of 



