124 



Discussion 



Table II (Hess) 

 Influence of tri-iodothyronine on ATP/ADP ratio in mitochondria 



Expl. No. 



1 

 2 

 3 



4 

 5 



shown in 1955 (Chance, B., and Hess, B. (1955). J. cell comp. Physiol, 46, 

 358). Prof. Chance has already mentioned the Qo^ values for this. The 

 underlying mechanism of these effects consists in a release of ADP by the 

 phosphorylation of glucose, then an activation of oxidative phosphoryla- 

 tion through this ADP and, finally, an inhibition of respiration after 

 reconversion of all available ADP to ATP in the mitochondria. Using 

 small amounts of glucose, without exhausting the ATP pool at the hexo- 

 kinase site, this blockage can be used as a titration point for determina- 

 tion of a glucose /oxygen ratio (see also Chance, B., and Hess, B. (1959). 

 Science, in press). Since ADP, through this mechanism, is quantitatively 

 taken up from the acceptor of the oxidative phosphorylation, the value 

 of the ratio should be about 3 according to the ADP/O ratio of iso- 

 lated mitochondria. In Table HI, some data (experiments 1-7) are 

 collected which were obtained by measurement of the oxygen uptake by 

 means of the rotating platinum electrode after addition of known 

 amounts of glucose. 



Table III (Hess) 

 Direct titration glucose/oxygen ratio 



Expt. No. 



1 

 2 

 3 

 4 

 5 



7 



8 



9 



10 



Ratio 



2-6 



3-5 



2-3* 



2-5* 



3-3* 



In presence of iodoacetate (0-8 mM). 



When one considers the increasing amounts of glucose added and the 

 increasing amounts of oxygen taken up, it is obvious that when plotted 

 they form a straight line. In order to define the pathway of this meta- 

 bolic interaction, the experiments have been repeated in the presence of 



