PURINE AND PYRIMIDINE ANALOGUES 295 



Discussion 



Reichard : Do you believe that the fluoronucleotides are less effective as donors 

 of the peptides, and connected with this question is the second question didn't you 

 find any uracil in your fluorouracil nucleotides ? 



Rogers : In answer to the first question we have taken the cells in which we have 

 accumulated the pyrimidine mucopeptide and have tried in all ways to obtain 

 utilization of them. We get no utilization of the small mucopeptide even when the 

 cells are incubated in the presence of a large excess of normal uridine. Our hypo- 

 thesis is that the fluorine-substituted compounds inhibit the polymer formation by 

 competitive inhibition of the final steps of condensation. We haven't any very good 

 evidence, but one can specifically prevent the accumulation of these materials by 

 adding uridine simultaneously with purines. The second question concerns uracil 

 again ; in preliminary experiments we have used half as much fluorouracil as those 

 I have shown today and under these conditions we got approximately equal amounts 

 of the uracil compound and the fluorouracil compound accumulating. When we 

 doubled the amount of fluorouracil, the normal uracil compounds completely 

 disappeared. 



