158 LARS ERNSTER 



requirement for phosphate acceptor in maintaining a high rate of respira- 

 tion, without parallel loss of the actual phosphorylating capacity. Such a 

 "loose-coupling" of phosphorylation from respiration, as revealed by an 

 increased respiratory rate in the absence of phosphate acceptor, was in the 

 present case accompanied by an almost complete abolition of the aceto- 

 acetate reduction. The phosphorylating capacity of the Mg++-deficient 

 system (measured with AMP as terminal phosphate acceptor) was the 

 same as that found in the presence of Mg++. As anticipated, no aceto- 

 acetate reduction took place in the presence of the terminal phosphate 



TABLE IX 



Influence of Mg++ on the Succinate-linked Reduction of 

 acetoacetate under various conditions 



(Azzone, Ernster and Weinbach, unpublished) 



Experimental conditions as in Fig. 13, except that mitochondria from 300 (in 

 Experiment 2, 200) mg. liver were added per flask. 



acceptor because of the continuous removal of the high-energy bonds 

 generated in the respiratory chain. These findings substantiate the above 

 conclusion that "loosely-coupled" respiration cannot give rise to suc- 

 cinate-linked DPN-reduction even though the phosphorylating capacity 

 of the mitochondria remains intact. 



Addition of ATP to the Mg++-deficient system restored the aceto- 

 acetate reduction (Table IX), but this effect was counteracted by EDTA, 

 suggesting that it was dependent on endogenous Mg++. The ATP effect 

 was not abolished by oligomycin A, and thus cannot be due to a 

 supply of energy to the respiratory chain. Furthermore, 10 mM sodium 



