Control of. Oxygen Utilization 



103 



CO 



O 



3k 



(\J 



o 



[Mg*-^] mM 



Fig. 9. Magnesium concentration required 

 for activation of the respiratory control 

 mechanism. Experimental conditions 

 similar to those of Fig. 8 : sucrose-EDTA- 

 phosphate medium, succinate as substrate. 

 (Expt. no. 470d) 



also occur in mitochondria subjected to cyclic changes in 

 magnesium concentration. 



Effect of calcium 



Calcium has for some time been recognized as an uncoupling 

 agent for mitochondria (Potter, 1947; Lehninger, 1949; 

 Slater and Cleland, 1953). Furthermore, its addition causes 

 loss of respiratory control or "decontrol", and the mechanism 

 of its action involves several novel facets that merit discussion 

 (Chance, 1956), especially in connexion with the effects of 

 ADP and magnesium. Fig. 10 is a polarographic recording 

 of the respiratory activity of a guinea-pig liver mitochondrial 

 suspension treated with glutamate as substrate. Addition of 

 135 (xM ADP causes an acceleration of respiration to a rate 



