NUCLEIC ACID IX SARCOMA SLICES 777 



Activity per mgm nucleic acid P: 



I (without KCN) 128; 

 II (with KCN) 0.6. 

 The total activity of Ihc Ringer's solution at the end of experiment 



I 0.85x106; 

 II 1.05x106. 



Activity of 1 mgm of nucleic acid P as a percentage of that con- 

 tained in the Ringer's solution 



I 1.5x10-2; 

 II 5.0x10-5. 



The above data show that in the absence of KCN an easily detectable 

 portion of the nucleic acid is active and therefore newly formed, and 

 that in the presence of KCN the formation of new molecules of nucleic 

 acid is decreased to i/g^Q of that observed in the absence of this addition. 

 In another experiment 1.3 xlO"^ of the final activity of the Ringer's 

 solution was found per mgm of nucleic acid P. 



In later experiments the Ringer's solution has been replaced by hepar- 

 inized rat's blood or plasma, and the activity of 1 mgm of free P in the 

 sections has also been determined at the end of the experiment in order 

 to permit calculation of the percentage of newly formed nucleic acid 

 (cf. the discussions on p. 774). 



Formation of Nucleic Acid in the Presence and Absence of NaF 



These experiments also were performed at 37° C; 7.56 gm of sarcoma 

 sections were immersed in 15 cm^ of rat's blood in l)oth experiments, 

 (a) and (b), 18.9 of radioactively labelled sodium phosphate at pH 7.4 

 and 8.1 mgm of NaCl at the physiological concentration being added in 

 experiment (a). In experiment (b) the same amount of sodium phosphate 

 was used but 6 mgm of NaF was added instead of NaCl. A mixture of 

 oxygen and COg was passed through the Erlenmeyer flasks for 15 min 

 before addition of the activity and then for 5 min in each subsequent 

 hour, at 37° C. After breaking off the 4 hr experiment the activity of 

 the purified nucleic acid, its P content, the activity of the free P of an 

 average sample of the slices and the P content of the latter were deter- 

 mined. The activity of 1 mgm. of nucleic acid P as a percentage of the 

 activity of 1 mgm of free sarcoma P was found to be: 



(a) without NaF, 0.126; 



(b) with NaF, 0.026. 



Activity of the free P in the whole of the tissue as a percentage of the 

 activity in the whole of the plasma plus the whole of the free P in the 

 tissue: 



