236 Van R. Potter and Hermann Niemeyer 



TPN. The effect of TPN will be discussed in a later section. 

 The effect of mitochondria could be related to the ATPase 

 activity of the preparation. When small amounts of mito- 

 chondria were added to the glycolytic system, a stimulation of 

 glycolysis coincident with less esterification of inorganic 

 phosphate was observed. This is considered as an indication 

 that the additional ATPase was enough to permit the main- 

 tenance of the orthophosphate, and to provide more phosphate 

 acceptor (ADP), which could be the limiting factor in the 

 overall process. It seems that the latter effect is the more 

 important, because the concentration of inorganic phosphate 

 in the medium is quite in excess of the requirements. Further- 

 more, the addition of ADP to the brain system without 

 mitochondria increased glycolysis. ADP also raised the 

 fraction of glucose consumed that appears as lactate, ar 

 effect that was similarly observed with the addition ol 

 mitochondria. 



When increasing amounts of mitochondria are added, 

 glycolysis diminishes and there is a net release of inorganic 

 phosphate. It appears that the breakdown of ATP decreases 

 the useful level of this compound in the medium, and thus 

 reduces glucose utilization. 



Effect of inorganic phosphate — The great sensitivity of the 

 system to inorganic phosphate was observed in spectrophoto- 

 metric studies. In these experiments, the reduction of DPN 

 was followed under certain conditions, using glucose or G-6-P 

 as a substrate. This process is strictly dependent on a con- 

 centration of inorganic phosphate that exceeds the stoichio- 

 metric requirements for the oxidation of 3-phospho-D- 

 glyceraldehyde, probably owing to the formation of fluoro- 

 phosphate (Fig. 3). In a similar system, DPNH may be 

 oxidized, which is interpreted as the reduction of dihydroxy- 

 acetone phosphate to a-glycerophosphate. When F-di-P is 

 used as the initial substrate the oxidation of DPNH is inde- 

 pendent of the concentration of inorganic phosphate, as has 

 to be assumed from the knowledge about the mechanism of the 

 particular reactions that participate. However, if glucose or 



