134 Albert L. Lehninger, et al. 



Table I 



Effect of uncoupling agents on partial reactions of oxidative 

 phosphorylation in fresh digitonin fragments 



Inhibition Inhibition 

 Concentra- of of Stimulation 



tion Uncoupling ATP-^^Pi ATP-ADP of 



action in intact mitochondria which is obviously different 

 from that of DNP, dicoumarol, and gramicidin ; elsewhere we 

 have shown that thyroxine causes changes in the mito- 

 chondrial membrane and consequent swelling, possibly by 

 an interaction with a bound form of diphosphopyridine 

 nucleotide (DPN) (Tapley, Cooper and Lehninger, 1955; 

 Lehninger, 1956; Lehninger, Ray and Schneider, 1959). 



There are three agents which uncouple phosphorylation and 

 inhibit the ATP-^^p. exchange, but which do not inhibit the 

 ATP-ADP exchange, namely azide, arsenate and methylene 

 blue. Clearly, the action of these three uncoupling agents 

 differs from that of DNP, dicoumarol and gramicidin; their 

 action must be in either reaction (1) or reaction (2) (or an 

 intervening reaction) but not in reaction (3) itself. The action 

 of arsenate is already known to be that of a competitor of 

 phosphate; presumably its site of action is in reaction (2). 

 Methylene blue by its chemical nature can be postulated to 

 replace or alter reactivity of a carrier component in reactions 

 (1) or (2). p-Chloromercuribenzoate (PCMB) differs from all 

 the rest of the agents since it inhibits all the partial reactions, 

 including ATPase activity. 



