Role of TPN. in Control of Glycolysis 



245 



ratio of the two activities depends markedly on the pH, as is 

 shown in Fig. 11. A similar influence of pH is found in the liver 

 (Navazio, Ernster and Ernster, 1957) and in Novikoff tumour 

 (Potter and Niemeyer, unpublished data). This fact and the 

 finding that the ratio of activities is different from one tissue 



Fig. 11. Influence of pH on DPN- and TPN- 

 linked dehydrogenase activities. The assay 

 mixture contained brain supernatant 0-4, [im 

 DPNH or TPNH, 5 [im pyruvate, Tris-maleate 

 buffer of variable pH and water to complete 3 • 

 ml. 



to another suggests that we are dealing with separate enzymes 

 (cf. Rutter and Lardy, 1959). At the pH of 7-4 used in the 

 glycolysis experiments, the activity of the TPN dehydrogenase 

 would be enough to permit the oxidation of about 0-9 (jlm of 

 TPNH by • 5 ml of the brain supernatant in 30 minutes. 



Addition of mitochondria — The addition of aged mitochond- 

 ria increased the inhibitory effect of TPNH, or converted 



