METABOLISM OF THE NUCLEIC ACIDS 



429 



NHz 



I 



IN CH Deaminase 



Cytosine 



N 



I 



HO-C 



OH 



I 



Uracyl 



CH 



II 

 CH 



-CH, 



(?) 



NH, 



I 

 HO-C 



5-Methylcytosine 



Y ^■"'3 Deaminase 



CH 



N* 



OH 



I 

 .C^ 



^NH. COOH 



C=0 + CHs 



\'u I 



^iis COOH 



Urea 



Malonic 

 acid 



Uracil 

 oxidase 



C-CH 



'Thymine 



HO-C^ .CH 

 Thymine 



oxidase 



Barbiturase 



OH 



I 



N^ ^CH 



I II 



HO-C^ X-OH 



Barbituric acid 



-CHj 

 (?) 



OH 



I 



N^ ^C-CHa 



HO-C^ _/C-OH 

 5-Methylbarbituric acid 



! CO2 



t + 



X(?) ->H,0 



+ 

 NH, 



Fig. 6. The catabolism of the pyrimidines in bacteria. 



acid is first demethylated to barbituric acid which is subsequently split by 

 the barbiturase to urea and malonic acid. 



VIII. Addendum 



Daoust et al.-"^ have repeated their previous studies on the rate of re- 

 newal of DNA in relation to mitosis, using lung alveolar tissue, and have 

 confirmed that the rate of DNA synthesis calculated from results on the 

 incorporation of P^- is twice that expected on the basis of new cell formation. 

 It is again concluded that all the DNA of the two cells formed in the 

 course of mitosis is newly synthesized. Malkin,^''^ on the other hand, has 

 found that C* is taken up by the DNA of mature sea urchin sperm when 

 incubated in vitro with glycine-2-C^'* or adenine-4 , 6-C^'*. Since these sperm 



2"' R. Daoust, F. D. Bertalanffy, and C. P. Leblond, /. Biol. Chem. 207, 405 (1954). 

 "2 H. M. Malkin, Biochem. et Biophys. Acta 12, 585 (1953). 



