Discussion 125 



• 8 mM iodoacetate as an adequate inhibitor of glyceraldehyde-3-phos- 

 phate dehydrogenase. Under these conditions the glucose/oxygen ratio 

 has an average value of 2 • 7 in agreement with our theory. Table IV 



shows similar data obtained in the presence of excess glucose. In these 

 experiments the initial disappearance of glucose (20 sec.) is measured by 

 chemical determination and correlated with the corresponding oxygen 

 uptake followed with the platinum electrode. The average value of the 

 glucose/oxygen ratio is 2 • 5. In consideration of the inorganic phosphate 

 taking part in this stoichiometry, the amount of glucose should be 

 equivalent to an amount of phosphate taken up through oxidative phos- 

 phorylation. This has been verified and Fig. 1 (p. 126) shows the kinetics 

 of inorganic phosphate after addition of a known amount of glucose. 

 In these experiments, the ascites tumour cells are suspended in a phos- 

 phate-free medium so that analysis of the centrifuged cells would show 

 the disappearance of the intracellular phosphate caused by glucose 

 addition. Fig. 1 shows the disappearance of phosphate during glucose 

 utilization for • 25 and • 5 [xm glucose. A comparison of the scale of the 

 ordinate with that of the initial glucose concentration added shows a 

 glucose/phosphate stoichiometry of approximately 1/1 in confirmation 

 of our theory. It is interesting that the phosphate level is not steady 

 following the utilization of glucose but rises again presumably due to 

 various dephosphorylation processes. 



In summary, these experiments^ demonstrate the possibility of 

 measuring the efficiency of phosphorylation in intact cells. 



Aldridge: To return to Dr. Backer's point: if we are to use informa- 

 tion from Warburg experiments to get information about how the mito- 

 chondria behave in the cell, we have to think rather carefully about the 

 media and conditions under which we examine them. The results which 

 I have already mentioned showing fourfold stimulation were obtained 



