Discussion 



289 



Under our experimental conditions, DPN reduction starts within a few 

 seconds after addition of glucose and reaches a maximum at 18 seconds. 

 Thereafter there is an oxidation of pyridine nucleotide resulting in a 

 steady state concentration of DPN very nearly as high as it was prior 

 to the addition of glucose. We can state, therefore, that there is no 



Aerobic 



Starved -^^;;22r^ 



t 

 l5mM 



10 20 

 Seconds 



Fig. 1A (Chance). (Expt. no. 177) 



lack of oxidized DPN in the cell at this time which would limit fermenta- 

 tion in the way illustrated by Prof. Holzer's Figs. 1 or 2. A similar 

 conclusion can be drawn with regard to the addition of glucose under 

 anaerobic conditions (Fig. IB) where even in the presence of 20 mM 



=340-374m>j= 

 log Io/r= 0.050 



6mM 

 glucose 



Anaerobic ) ' 

 Steady- State >->• 

 (20mM EthanoD) 



Fig. IB (Chance). (Expt. no. 321c) 



ethanol the characteristic fluctuations of the steady state of reduced 

 pyridine nucleotide result in considerably more DPN in the cell than 

 was present prior to the addition of glucose. It seems, therefore, that 

 the theory of a DPN limitation of fermentation one or two minutes 

 after the addition of glucose is without direct experimental support on 

 the basis of the assay of the total DPN within the cell ; if, indeed, DPN 



CELL METAB. — 10 



