Role of TPN in Control of Glycolysis 



247 



of mitochondria or without them (Fig. 5). In view of this lack 

 of differentiation between TPN and TPNH effects, which is 

 attributed to turnover of the coenzymes, and the fact that 

 TPN did not inhibit directly the enzymes concerned in glycoly- 

 sis, the possibility was considered that the triphosphopyridine 

 nucleotides acted catalytically, producing indirectly some 

 inhibitor. 



Effect of 6-Phosphogluconate 



There is evidence that 6-PG is able to inhibit competitively 

 phosphohexoisomerase from different sources (Parr, 1956, 



lI.2- 



CONTROL^ .083 QU./MIN. 

 + 6-PG= .035 » (-58%) 



6-PHOSPHOGLUCONATE 

 (3pM) 



5 10 15 



TIME (MINUTES) 



Fig. 13. Effect of 6-phosphogluconate on the reduction of 



DPN by G-6-P. The composition of the medium was 



similar to that used in Fig. 6, right, 6 [iM G-6-P were used 



as initial substrate. 3 [im 6-PG when indicated. 



1957). As TPN could act indirectly by producing 6-PG from 

 G-6-P, the effect of 6-PG was investigated. It was shown that 

 6-PG strongly inhibited glucose uptake, lactic acid production 

 and phosphate uptake, as shown in Fig. 12. Its effect is, in 

 general, more pronounced than that of TPN or TPNH, and is 

 also dependent on the pH of the system. 



The effect of 6-PG was also shown in a system in which DPN 

 was reduced with G-6-P as the initial substrate (Fig. 13). The 



