THE FUNXTIONAL LINK OF SUCCINIC DEHYDROGENASE 



195 



[Oj]=0 



Fig. 2. Stimulation of succinate oxidation by ATP in rat liver mitochondria 

 preincubated with arsenate and dicoumarol [5]. Experimental conditions as in 

 Fig. I. 0001 M ATP (ATP) was added at the point indicated. 



oxidation, as a consequence of the resynthesis of high energy intermediates 

 taking place during the oxidation of succinate. When this resynthesis was 

 aboUshed by the presence of an uncoupling agent, the depression of 

 succinate oxidation became permanent. Under these conditions, added 

 ATP was required for stimulating the oxidation of succinate (Fig. 2). No 

 stimulation of the oxidation rate was observed when ATP was replaced by 

 AMP or EDTA. 



TABLE I 



Depletion of Mitochondrial Endogenous Phosphate by Arsenate and 

 Protection by Succinate 



"*-P-labelled mitochondria" from 500 mg. rat liver (wet weight) were incubated 

 in open tubes at 30. After 7 min., i ml. of the incubation mixture was filtered 

 through a Celite layer as reported elsewhere [12]. Each tube contained in a final 

 volume of 5 ml.: 0-05 M KCl, 0-03 M tris buffer pH 7-5, 0-125 ^ sucrose, and 

 when indicated o-oi M succinate, 0-003 ^' arsenate, 2 /(g. antimycin A, o-ooi M 

 KCN. As in Table II and III, the number of counts is here indicative of the 

 amounts of endogenous phosphate which remained in the mitochondria after 

 preincubation. 



Additions 



Counts/min. ( x 10 ^) 



None 

 Arsenate 

 Succinate 



Arsenate + succinate 

 Arsenate + succinate + 



Antimycin A 

 Arsenate + succinate + KCN 



700 



100 (14 •4°,,) 

 521 (73-5"o) 

 421 (6o-2<'o) 



223 (3i-9"o) 

 128 (18-30,.) 



