Control of Oxygen Utilization 



111 



apparently overlap to such an extent that no inflexion of the 

 spectrophotometric eff'ect is observed at DIB concentrations 

 corresponding to maximal respiratory activity. 



With most uncoupling agents, it is difficult to observe their 

 effect upon the steady-state level of reduced pyridine nucleo- 

 tide because of their absorption in this region. With DIB, 



100- 



o 



6 



X 



o 



CO 



I 



50' 



10 



T 1 1 1 1 1 1 



log [dIb] (mIO'^ 



Fig. 15B. Comparison of the spectroscopic effects of DIB 

 on reduced pyridine nucleotide and cytochrome b of 

 guinea-pig kidney mitochondria; glutamate as sub- 

 strate. (Experiment carried out in collaboration with 

 Dr. G. HoUunger.) (Expt. no. 658a) 



however, measurements of reduced pyridine nucleotide at 

 350 m[jL with respect to 374 m^x are relatively insensitive to its 

 absorption. It has, therefore, been possible to make a titra- 

 tion of the effect of DIB upon reduced pyridine nucleotide. 

 Oxidation of both reduced pyridine nucleotide and cytochrome 

 b is indicated in the graph of Fig. 15B in which the results are 

 plotted as percentages of the maximal effect. It is seen that 

 the curves are very similar in shape and that half-maximal 



