240 



Van R. Potter and Hermann Niemeyer 



importance of the level of oxidation of the TPN on the 

 magnitude of its effect. 



Effect of impurities — With the spectrophotometric method 

 it was shown that commercial TPN inhibited the glycolytic 

 chain at different levels. When the reduction of TPN by 



a. 

 E 



o ■ 



fO 



t-4 



to 



2 

 Q .3 



< 



Q. 

 O 



10 20 30 40 10 20 30 40 10 20 30 40 

 TIME (MINUTES) 



Fig. 6. Influence of ethylenediaminetetra-acetic acid and 

 of treatment with Dowex-50 on the effect of TPN on some 

 reactions of the glycolytic chain. In the left and central experi- 

 ments the composition of the reaction mixture was as follows : 

 0-1 ml. brain supernatant, 100 \jm Tris buffer pH 7-46, 12 fxM 

 glucose, 6 [LM. ATP, 12 piM-MgClg. In the control vessels 1-2 

 [ZM TPN was present. 1 \p,i ethylenediaminetetra-acetic acetate 

 was added when indicated. In the experiment at the right, the 

 3-0 ml. contained: 0-2 ml. of brain supernatant, 5 \lm F-di-P, 

 100 [XM Tris, 70 (jlm sodium arsenate, 180 [zM-NaF, 6 [xm DPN, 

 and 6 [jtM-MgClg. 



G-6-P was studied, it was shown that there was not any 

 influence of the level of TPN on the rate of its reduction. 

 But, when glucose was used as the initial substrate, the 

 increasing concentration of TPN increased the lag phase and 

 decreased the slope of the line representing the reduction of 

 TPN (Fig. 6). As the G-6-P dehydrogenase capacity of the 

 brain supernatant exceeds that of hexokinase, and as the 



