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E. Racker and R. Wu 



of glucose is very rapid. Then follows a short period of almost 

 complete cessation of uptake, a phenomenon first observed by- 

 Chance and Hess (1956). The resumption of glucose uptake 

 proceeds then at a rate considerably below the initial one. 

 The complete block of glucose uptake, despite a high intra- 

 cellular concentration of ATP, was a rather puzzling feature 



0) 



o 

 o 



3 



O 

 CO 



MINUTES 



Fig. 2. Effect of DNP on the kinetics of glucose 



uptake 



Experimental conditions were as in Fig. 1, except 



that the ascites cells were preincubated for 15 



minutes with or without DNP (10"* m). Curve 1 



without, curve 2 with DNP. 



of this phenomenon. In order to explore this further, the cells 

 were pretreated with DNP to allow the intracellular ATP to 

 be depleted. After addition of glucose, the rate of glycolysis 

 and the levels of ATP were determined at frequent intervals 

 (Fig. 2). After a short lag, the rate of glucose uptake was 

 maximum at a time when the ATP levels were one-fourth that 

 of the DNP-less control, which glycolysed at a considerably 

 slower rate. 



It seems apparent that the level of ATP, as measured in the 

 extract after breaking up the cells, cannot be correlated to its 



