FREE DEOXYRIBONUCLEOTIDES IN RADIATION DAMAGE 159 



relatively homogeneous and does not change after irradiation. Accord- 

 ing to Holmes (11)56) DNA-synthesis progresses most intensively 24 hr 

 after ])artial he])atectomy and the ince]ition of the synthetic period is 

 delayed by \'2 hr by irradiation in the presynthetic period. 



The deoxyribosides were detected by the microbiological method 

 of Hoft'-Jorgensen (1952), the nncleotides were separated from nncleo- 

 sides on a colnmn of strong anion-exchanger at pH 7-(). Nucleotides 

 were converted into nucleosides by means of an enzymatic preparation 

 from snake venom before microbiological determinations. 



In the first experiment, the rats were irradiated with a dose of 600 r 

 1 hr after partial hej^atectomy. The deoxyribose compounds were de- 

 termined 25 hr following hepatectomy. Four groups of rats were in- 

 vestigated concurrently viz. hepatectomized irradiated rats, only 

 hepatectomized rats, only irradiated rats and control rats. Irradiation 

 and hepatectomy resulted in an increase in the level of free deoxyribo- 

 sides (Table III). The highest level was observed in irradiated hepatec- 

 tomized rats. On the other hand, the deoxynucleotide content was 

 highest in non -irradiated hepatectomized rats. The deoxyribonucleo- 

 ticle content was the lowest in the control rats. Irradiation itself thus 

 resulted in a certain rise of free deoxyribonucleoticles, but the further 

 rise produced by hepatectomy was blocked by irradiation. 



Table III. The effects of partial hepatectomy and of total-body irradiation 

 on the content of free deoxyribosides and deoxyribotides in liver 



Group No. of Deoxynucleosides Deoxynucleotides 



animals (/^g/g tissue) {/xg/g tissue) 



The irradiation followed 1 hr after hepatectomj', the rats were killed 25 hr after 

 hepatectomy and/or 24 hr after irradiation. 



In the next similar experiment (Table IV), the rats were already 

 irradiated 24 hr before hepatectomy. In this experiment, the nucleo- 

 tides were not separated from nucleosides and all deoxynucleotidic 

 compounds were determined together after enzymatic conversion to 

 deoxyiuicleosides. The total level of all deoxyribosidic substances in 

 the individual experimental and control groups Avas similar to that in 

 the preceding experiment. It seems thus, that deoxyribotide synthesis 



