242 



Van R. Potter and Hermann Niemeyer 



concentrations of TPN than those used in the complete 

 glycolytic system. In Fig. 8 the dashed line indicates the 

 inhibition of hexokinase that one would expect with the 

 amount of supernatant used in the complete system. At the 

 concentration usually employed in this kind of experiment, 

 the percentage of inhibition would be negligible. The possible 



80- 



60- 



GQ 



8-» 



20- 



TPN REDUCTION 

 (GLUCOSE SUBSTRATE) 



.Iml Brain-S, 



.2 ml 



3 ml 

 .5ml(theor.) 



TPN (>iM) 



Fig. 8. Influence of the amount of brain supernatant on the 

 inhibition of hexokinase activity by TPN. The data are taken 

 from the same experiment of Fig. 7. The dash hne indicates the 

 expected inhibition if • 5 ml. is used, calculated by extrapolation. 



metal contamination would not explain, on the other hand, the 

 influence of mitochondria on the effect of TPN. Nevertheless, 

 in further experiments with the glycolytic system the purified 

 preparation of TPN was always used, with results absolutely 

 comparable to those obtained with the non-purified form, 

 when glucose and lactic acid were determined. 



The general conclusion of these experiments was that TPN 

 did not inhibit directly any of the enzymic reactions analysed, 

 but could inhibit indirectly the overall process of glycolysis, 

 an effect that was enhanced by the presence of mitochondria. 



