Originally published in Arkiv for Kemi 4, 20 (1951). 



81. EFFECT OF X-RAYS ON THE INCORPORATION OF ^^C 

 INTO TISSUE FRACTIONS OF THE MOUSE 



G. Hevesy and G. Dreyfus 

 From the Institute for Researcli in Organic Chemistry. University 



of Stockholm 



Mitotic arrest is possibly the most conspicuous early effect of ionizing 

 radiation on the living organism. From the view-point of the chemist, 

 cell division is a result of intense and properly correlated cellular synthe- 

 sis. Correspondingly, one expects the mitotic arrest to be due, at least 

 partly, to an interference with some of these synthetic processes. It 

 was found already several years ago, that irradiation of rat Jensen 

 sarcoma with an X-ray dose of some hundred r interferes with the 

 formation of desoxyribo nucleic acid in the sarcoma^^). In these experi- 

 ments the rate of incorporation of ^"^P administered as sodium phosphate 

 into the desoxyribo nucleic acid of the sarcoma of irradiated and control 

 rats was compared. The former were found to take up much less ^sp 

 than the controls. While some of this difference was due to the different 

 rate of penetration of ^^p into the sarcoma cells, a very appreciable part 

 of it had to be ascribed to an about 50 per cent inhibition of desoxy- 

 ribo nucleic acid formation. Similar results were obtained from investiga- 

 tions of normal organs of the rat. The blocking effect of radiation on 

 the formation of labelled desoxyribo nucleic acid was already obser- 

 ved 1/2 hour after irradiation took place. 



An objection raised to our results was that the incorporation of ^^P 

 with desoxyribo nucleic acid may indicate a re-phosphorylation of the 

 molecule only. An enzymic splitting-off of phosphate groups may be 

 followed by a re-phosphorylation process which in the presence of label- 

 led phosphate, labelled ATP or another phosphate donor results in an 

 incorporation of ^sp with the desoxyribo nucleic acid molecule. Though 



^'^' The bibl. of earUer works, the first paper published being that of H. Euler 

 and G. Heve.sy, Kgl. Danske Videnskah. Selslab Biol. Medd. 17, 8 (1942) is to 

 be found in G. Hevesy's contribution to Adv. of Biol, and Med. Physics (1948) 

 1, 409; see also B. Holmes, Brit. Journ. Bad. 20, 450 (1947) 22, 487 (1949); G. 

 Hevesy, Nature 163, 809 (1949); L. S. Kelly and H. B. Jones, J. Soc. Exp. 

 Biol. Med. 74, 493 (1950); H. Jones, Hep. Oberlin. College Symp. (1950) in print. 

 A. Howard and S. R. Pelc, Ciba Foundation Conference on Isotopes in Bioche- 

 mistry p. 147. London (1951). 



