196 GIOVANNI FELICE AZZONE 



The concept that intact mitochondria have a strict requirement for high 

 energy phosphate and not merely of inorganic phosphate in order to main- 

 tain a high rate of succinate oxidation is supported further by the following 

 findings. 



Fig. 3. Correlation of the inhibition of succinate oxidation with the depletion 

 of mitochondrial phosphate. Mitochondrial endogenous phosphate measured as 

 described in Table I. 



[O2] = 



[O2]=0 



Fig. 4. Prevention of the inhibition of succinate oxidation by amytal [6]. 

 Experimental conditions as in Fig. i. coca m amytal was added at the point 

 indicated. 



The presence of a five-fold molar excess of inorganic phosphate during 

 the preincubation of the mitochondria with arsenate completely prevented 

 the inhibition of succinoxidase activity. On the other hand, if the same 

 concentration of inorganic phosphate was added to the mitochondria after 



