DISCUSSION 



formate ^'*C into DNA, while showing only slight inhibition on the uptake 

 of adenine ^'*C into DNA, It appears therefore that folic acid antagonists, 

 unlike X-rays, do not affect significantly the assembly of the DNA molecule 



Table I. Effect of Aminopterin on uptake of ^^C into DNA 

 on formate ^^C uptake into DNA 



* Old aminopterin solution 



from its constituents (purines and pyrimidines, desoxyribose, phosphate) 

 but inhibit the synthesis of pyrimidines, and, probably to a lesser extent, 

 that of the purines. Citrovorum factor, in a concentration of 75 [xg/ml 

 medium reverses the inhibiting effect of aminopterin. 



This work is part of a project supported by the British Empire Cancer Campaign. 



^ Lajtha, L. G. 



2 Lajtha, L. G. 



3 Lajtha, L. G. 

 * Lajtha, L. G. 

 ^ Lajtha, L. G., 



REFERENCES 



J. Clin. Path. 1952, 5 67. 



Nature, Lond. 1954, 174 587. 



Exp. Cell. Res. 1952,3 696. 



J. Photogr. Sci. 1954, in press. 



Oliver, R. and Ellis, F. Brit. J. Cancer, 1954, in press. 



* Howard, A. and Pelc, S. R. 

 London. 



Isotopes in Biochem. Ciba Conf. 1951, Churchill, 



DLSCUSSION ' 



R. Oliver : It has been shown that radiation prevents the incorporation into 

 DNA of adenine added to the culture. However, it is not at present clear whether 

 this is due to interference with the synthesis of the other necessary purines or with 

 the assembly of the DNA molecule. As an extension of the work reported here it 

 is suggested that ^*C labelled adenine be added to the irradiated culture together 

 with the other three purines required. If then it is only the purine synthesis which 

 is inhibited DN.-\. synthesis should be able to proceed as indicated by incorporation 

 of the labelled adenine. The radiation effect on each purine synthesis could be 

 investigated in this way. 



219 



