676 



ADVENTURES IX RADIOISOTOPE RESEARCH 



Specific Activity of the Nucleic Acid Phosphorus Extracted from the 



Total Rat 



In another experiment the specific activity of both the total clesoxy- 

 ribo nucleic acid P and the total ribo nucleic acid P extracted from a 

 rat weighing 194 gm was determined. The activity of labelled sodium 

 phosphate amounted to 8.1 microcuries per 100 gm animal weight. The 

 time of the experiment was 2 hours. The results of this experiment 

 are seen in Table 2. 



Table 2. — Specific Activity of the Nucleic Acid P Extrac- 

 ted FROM THE Total Rat Compared with the Corresponding 

 Values for Liver, Spleen, and Inte.stinal Mucosa. The 

 Value for the Specific Activity of the Total Rat Ribo P 

 IS Assumed to be = 100 



As shown in Table 2, the specific activity of the average nucleic 

 acid P of the rat is almost identical with the corresponding value of 

 the ribo and desoxyribo nucleic acid, respectively extracted from the 

 intestine. 



The interpretation of the significance of the specific activity figures 

 obtained for the total rat encounters some difficulties, as the specific 

 activity of the free P utilized in the formation of the labelled nucleic 

 acid molecules is unknown. If the specific activity of the free P utilized 

 in building up the average body nucleic acid would correspond to the 

 specific activity of the free liver P, the percentage "rate of renewal" 

 of the body ribo and desoxyribo nucleic acids would be 2.0 and 1.2, 

 respectively. If the specific activity of the free P utilized in building 

 up the average nucleic acid of the organism would correspond to the 

 specific activity of the intestinal P, larger figures, i.e. 3.6 and 2.2, 

 respectively, would be obtained. 



When calculating the last mentioned figures, we compared the specific 

 activity of the nucleic acid P at the end of the experiment with the spe- 

 cific activity of the free intestinal P at the end of the experiment. Cor- 

 rectly we should have considered the mean value of the specific activity 

 of the tliree intestinal P prevailing during the experiment. The mean 



