Control of Oxygen Utilization 95 



heart mitochondria suspended in suerose-ethylenediamine- 

 tetra-acetic acid (EDTA) medium (Slater and Holton, 1954; 

 Chance and M. Baltscheffsky, 1958). Again the mitochondria 

 are pretreated with substrate and suspended in the aerated 

 medium. Prior to the addition of ADP, the respiration rate 

 is -11 [JIM Og/sec. ; following the addition of ADP, the respira- 

 tion rate rises to 1 -7 and, after 64 [xm Og has been consumed, 

 drops abruptly to 0-08. Thus, the ratio of the rate prior to 



J 



rO.OB^iMO^/sec. 



Aerobic Mitochondria ^^390;jM ADP 



plus TrriM glutamote ~^^ »— -+ , 



56;jlVl 02 ^^';^>'M O p/sec 



ADP/ 0=3.5 ^.^ ^ — ^ Hj^ro 1 n 



Guinea pig liver mitochondria 



Fig. 2C. Control of respiration in a guinea-pig liver 

 mitochondrial suspension. The respiratory control ratios 

 here are among the highest observed for this experi- 

 mental technique. (Expt. no. 372) 



the addition of ADP and after the exhaustion of the added 

 ADP exceeds 20 : 1. Fig. 2C gives the highest values of 

 respiratory control that have been observed in our experi- 

 ments; these were obtained with guinea-pig liver mitochondria. 

 The substrate-treated mitochondria give a respiration rate 

 of • 03, which is increased to 1 • 3 by addition of 390 ^m-ADP. 

 After expenditure of the added. ADP, the rate falls to 0-02. 

 In this case, the ratio of the rates in the presence of ADP to 

 those following the exhaustion of added ADP is apparently 

 65 : 1. 



Experimental data on the optimal values of respiratory 

 control obtained in mitochondria isolated from a variety of 



