Originally published in Nature, 163, 8G9 (1949). 



79. EFFECT OF X-RAYS ON THE INCORPORATION OF 

 CARB0N-I4 INTO DESOXYRIBONUCLEIC ACID 



G. Hevesy 



From the Institute for Research in Organic Chemistry and the Pharmacological 

 Laboratories of the Karolinska Institute, Stockholm 



It was observed by several experimenters^^^ that the incorporation of 

 phosphorus-32 into desoxyribonucleic acid of the Jensen-sarcoma, and 

 also of normal organs, of the rat is markedly reduced by irradiation 

 with an X-ray dose of some hundred Roentgen. This result strongly 

 suggests the explanation that the rate of formation of desoxyribonucleic 

 acid is reduced by the effect of ionizing radiation. We studied recently 

 the effect of X-rays on the incorporation of carbon-14 into the purines 

 of desoxyribonucleic acid in the organs of rapidly growing rats. 



About five microcuries of carbon-14 incorporated with the carboxyl 

 group of sodium acetate were injected subcutaneously to each of 91 one- 

 to three-week-old rats. The rats were killed after the lapse of six hours, 

 and the desoxyribonucleotides were separated from the proteins by 

 extraction with hot trichloroacetic acicp); the purines obtained by hydro- 

 lysis were twice precipitated as silver salts and their radioactivity was 

 measured. Previous to the extraction of the kidney and muscle proteins, 

 20 mgra of desoxyribonucleic acid, kindly presented by Prof. Hammars- 

 TEN, were added to the trichloroacetic acid extract. Half the rats were 

 previously irradiated with a dose of 950 r., the voltage applied being 

 165 kV. 



As shown by the figures in the accompanying table, the amount of 

 labelled purines formed in the irradiated rats was about half the amount 

 formed in the controls, which is very similar to the reduction in the 

 incorporation of phosphorus-32 observed earlier^i). 



The rate of incorporation of carbon-14 into the proteins was not 

 reduced by irradiation; even some increase was observed, which may be 

 due to a decrease in the metabolic-rate produced by irradiation and 

 leading to an increased level of carbon-14 in the liver and intestinal 

 mucosa, corresponding to a greater incorporation of carbon-14 into tlie 

 proteins of these organs. The fact that, despite the increased carbon-14 

 content of the proteins of the irradiated rat, we observed a markedly 

 reduced incorporation of carbon-14 into the purines of desoxyribonucleic 

 acid of such rats clearly indicates a reduced rate of formation of the 



