EFFECTS OF THYROXINE AND RELATED COMPOUNDS ON LIVER .MITOCHONDRIA 11 



preincubation 

 • = min 

 o = 1 5 .. 

 D = 30 .. 

 X = 60 .. 



10 



10"" lO"-" 10' 



M Desam i not hyroxine 



Fig. 5. Lacking effect (jf preincubation on the desaminothyroxine sensitivity 

 of the ATPase activity of mitochondrial fragments prepared according to Kielley 

 and Kielley [80]. Experimental conditions as in Fig. 2. 



Comparison 7cit/i other A TPasc inhibitors 



A further characterization of the effect of desaminothyroxine on the 

 mitochondrial ATPase reactions was considered possible by comparing it 

 with the effects of known ATPase inhibitors. 



It has been known for some time that the liver mitochondrial ATPase 

 reactions are inhibited by azide [75, 81 83] and by a number of flavin 

 antagonists, including atebrin [76] and chlorpromazine [77]. The effect 

 of the flavin antagonists on the dinitrophenol-induced ATPase is diphasic, 

 consisting of a stimulation at low concentrations and an inhibition at high 

 concentrations [76, 77]. Figure 6 compares the effects of desaminothy- 

 roxine, azide, atebrin and chlorpromazine on the dinitrophenol-induced 

 ATPase activitv on the basis of concentration. Desaminothyroxine was the 

 most potent of the four inhibitors, and its effect lacked the dual character 

 shown by the flavin antagonists. 



