Control of. Oxygen Utilization 



107 



Lehninger (this symposium, p. 140) is comparable in its effect 

 with low concentrations of the substance described here. 



These data make it evident that respiratory control can be 

 diminished by a number of compounds without necessarily 

 interfering with the thermodynamic efficiency of the cell in its 

 energy conservation reaction. 



Effect of uncoupling agents 



Fig. 12 illustrates the effect of dicoumarol upon the respira- 

 tory rate of rat liver mitochondria with p-hydroxybutyrate as 



10 



20 



30 



[Dicoumarol] jjM 



Fig. 12. Effect of dicoumarol upon the respiratory rate of 

 a rat liver mitochondrial suspension; [B-hydroxybutyrate 

 as substrate. The respiratory rate obtained with excess 

 ADP in an independent experiment is indicated by the 

 arrow. (Expt. no. 468c) 



substrate. The respiratory rate increases with dicoumarol 

 concentration, rises to a maximum value, and then declines 

 at higher dicoumarol concentrations. The concentration 

 required for half-maximal activation of respiration is 4 (xM. 

 It is significant that the rate obtainable in the presence of 

 ADP and in the absence of dicoumarol is the same (see arrow, 

 Fig. 12).^ 



Since it has been postulated that dicoumarol has a specific 

 effect upon electron transfer between reduced pyridine 

 nucleotide and cytochrome h that differs from its effect upon 



