Control Points in Phosphorylating Respiration 137 



Table II 



Action of azide on sensitivity of ATP-ADP exchange to DNP 

 and dicoumarol 



System contained 0-003 m-ATP, 0-002 m-ADP-i*C, digitonin fragments 

 (50 [ig. N), pH 6-8, in total volume of 0-50 ml. Incubated 20 minutes at 23°. 



Additions 



ATP-ADP exchange 

 m^imoles ATP- "C formed 



of azide or of ageing. PCMB must act on reaction (3), but it is 

 not excluded that it may also react at other points in the 

 scheme. 



The relationships developed are summarized schematically 

 in Fig. 2. It must be repeated that additional group -transfer 

 reactions may intervene between reactions (1) and (2) and 



THYROXINE? 



(1) CARRIERj^£j3_ 



Q 



I 



+ carrier' 



-) CARRIERqj^'*-'(^ + carrierj.gjj 



H^O (CAUSE OF ATPASE) 



^^ 



STIMULATED BY 

 DNP, DICOUMAROL 



^CARRIER + (xj 



(2) CARRIERqx~(x) + Pi ^ 



± CARRIER, 



ARSENATE 

 COMPETES 



X 



P-® 



INHIBITED BY AZIDE, AGEING 

 IONIC STRENGTH, SUCROSE 



(3) P'>'(X) +ADP ^ 



f* ATP +(x) 



INHIBITED 

 BY PCMB 



Fig. 2. Relative sites of action of uncoupling agents in postulated 



mechanism. 



