Control of. Oxygen Utilization 



97 



which shows a ratio several-fold greater than can be obtained 

 with succinate. Thus, the values for toad heart muscle and 

 ascites tumour cells, both of which were measured with 

 succinate, would probably have been much larger had a 

 DPN-linked substrate been used. 



200 400 

 [ADP] (>jM) 



Fig. 3. The dependence of respiratory rate 

 upon the added ADP concentration: guinea 

 pig liver mitochondrial suspension with 

 glutamate as substrate. Half-maximal ac- 

 celeration is obtained in 20 (jlm ADP. (Expt. 

 no. 379c) (From Chance and Williams, 1955a. 

 Reproduced by permission of the Editors, J. 

 biol. Chem.) 



ADP and phosphate affinity of isolated mitochondria 



By measurements of the stimulation of respiratory rate in 

 response to additions of small concentrations of ADP, it is 

 possible to obtain a measure of the ADP affinity of the 

 respiratory chain. The vibrating platinum electrode is 

 especially suitable for this type of experiment since its rapid 

 response allows the measurement of respiratory rate a few 

 seconds after adding a very low concentration of ADP. 

 Fig. 3 indicates the effect of ADP concentration upon respira- 

 tory rate for a guinea-pig liver preparation with succinate as 



CELL METAB.— 4 



