96 



uncouples oxidative phosphorylation by interfering with £*, then 

 we have to show that it can disturb £* at these concentrations, at 

 10'^ Ai. and do something even in a 4 X 10~^ A( concentration. 

 The experiment showed that the phosphorescence of a 10~* Al ribo- 

 flavine solution is strongly quenched by 10~^ M dinitrophenol and 

 4.10"® still had a marked effect. So our experiment /"« vitro agrees 

 with the assumption that the oxidative phosphorylation, m vivo, 

 is uncoupled by interfering with £*, and more specifically, inter- 

 fering with the triplet £* of the riboflavine, tuned to its function 

 by the O2 present. 



In a way, the quenching action of dinitrophenol on the phos- 

 phorescence of riboflavine can be called specific. In 10"* M con- 

 centration the nitrophenol did not appreciably diminish the phos- 

 phorescence of other substances, such as acridine or atebrin, nor 

 that of rhodamin, even if it was increased by thiamine. In higher 

 concentrations the dinitrophenol absorbs light appreciably and so 

 the decrease in phosphorescence of other substances in its presence 

 could be ascribed to a direct absorption of the exciting light by 

 the nitrophenol. The quenching observed in this case is not a "true 

 quenching." 



2,4-DINITRONAPHTHOL 



This substance is but a dinitrophenol with an extra antenna, 

 another benzene ring added to it. Accordingly, we can expect it 

 to interfere with £* somewhat more strongly than did 2,4-dini- 

 trophenol. 



The experiment in vitro shows that 2,4-dinitro-l-naphthol sup- 

 presses the phosphorescence of riboflavine in vitro about four 

 times more strongly than does the corresponding dinitrophenol, 

 which is to say that the naphthol can be applied in one- fourth the 

 concentration and produce the same effect. M. Middlebrook com- 

 pared the action of the two drugs on the oxidative phosphorylation 

 of rat mitochondria. Her results are summed up in Fig. 24. As can 

 be seen, the dinitronaphthol inhibits oxidative phosphorylation 



