60 



E. C. Slater and W. C. Hulsmann 



and a sharp break in the rate when all the ADP is phos- 

 phorylated. These experiments were carried out manometric- 

 ally with reaction mixtures containing Mg2+. The rapidity 

 with which the new rate of respiration sets in after the 

 addition of ADP and the sharpness of the "cut-off" when all 



20 25 



TIME (MINS.) 



Fig. 1. Respiratory control in rat liver mitochondria. Reaction 

 mixture: phosphate, pH 7-4, 0-016 m; NaF, 0-012 m; MgClg, 0-006 m; 

 KCl, 0-083 m; ATP, 10"* m; ethylenediaminetetra-acetate, 0-001 m; 

 glutamate (dl), 0-007 m; sarcosomes, 0-6 mg. protein/ml. Reaction 

 vol., 1 ml.; temp. 25°. Phosphate acceptor (a mixture of AMP and 

 ADP) was added at the arrow. The measurement of Oj uptake com- 

 menced 8 min. after the beginning of the experiment. The P/0 ratio, 

 calculated from the amount of Og required to phosphorylate the 

 amount of phosphate acceptor added, was 2-60. 



the ADP is phosphorylated are shown more clearly in the 

 experiments of Chance and Williams (1955), who followed 

 the change of oxygen concentration with an oxygen electrode. 

 The requirement of ADP and inorganic phosphate for 

 intracellular respiration can be accounted for by the following 

 formulation of oxidative phosphorylation, which is an 

 elaboration of that suggested earlier (Slater, 1953). Indeed, 

 the elaborations are unnecessary to explain the effect of ADP 



