296 PETER REICHARD 







II I!, ^ 



HNf^^XH CH.N. CH3-NfeV:H hcooh . CHs-N^ «^H 



I2 4 *- ^ U 4 II *- ^ I2 4 II 



=C!3;CH 0=C' 3^CH 0=Ct^3^CH 



T^cetylribose Is'-acetylribose N 



H 



Acetylated uridine Acetylated l-methyluridine 1-Methyluracil 



0=i 



./«■ 



'HCl 



CH,-NH2 + NH, 

 Fig. 7. Degradation of uridine according to Lagerkvist.'"* 



1. Small Molecules as Precursors 



In their experiments with N^^-labeled ammonium citrate, Barnes and 

 Schoenheimer^ demonstrated the incorporation of the isotope into poly- 

 nucleotide pyrimidines in pigeons and rats. This, together with the simul- 

 taneous demonstration of the W^ incorporation into the purines, was the 

 first evidence that polynucleotide compounds were rapidly synthesized from 

 simple precursors. 



The results of Bergstrand et al.'^'^ that the isotope from glycine-N^^ is 

 incorporated into polynucleotide pyrimidines are explained by incorpora- 

 tion via the "nitrogen pool." The intact glycine molecule has been shown 

 not to be involved by Heinrich and Wilson ,^^ who could not demonstrate 

 any activity in polynucleotide uracil in the rat after administration of 

 glycine-l,2-C'^ 



The distribution of N^^ in the uracil ring after administration of N^^- 

 labeled ammonium salts to rats was studied by Lagerkvist.^" The degrada- 

 tion of the uracil was carried out by a method described earlier by the 

 same author. ^°^ It consisted in the preparation of the 1 -methyl derivative 

 of the acetylated uridine. After hydrolysis to 1-methyluracil, the uracil 

 ring was degraded and position 1 obtained as methylamine, while ammonia 

 represented position 3 (Fig. 7). The results of the degradation after adminis- 

 tration of N'^-labeled ammonia showed that under the experimental condi- 

 tions chosen by Lagerkvist the isotope content of position 1 was 3 to 4 times 

 higher than that of position 3. 



Investigations on the carbon precursors of polynucleotide pyrimidines 

 showed that position 2 was derived from CO2 in the rat (Heinrich and Wil- 

 son*^). This finding has been confirmed by Lagerkvist. ^"^ The report by the 

 latter author that CO2 is also a specific precursor for carbon 4 of uracil is 

 not valid since the degradation used in these experiments has now been 



10* U. Lagerkvist, Ada Chem. Scand. 4, 543 (1950). 

 los U. Lagerkvist, Acta Chem. Scand. 4, 1151 (1950). 



