824 ADVENTURES IN RADIOISOTOPE RESEARCH 



Comment on papers 79 — 82 



After observing a depressed ^^p incorporation into DNA of the irradiated rat, 

 we investigated the effect of exposure on i*C incorporation into the purines of 

 DNA of various organs. The only i*C labelled material at our disposal being at 

 that date sodium acetate, we studied acetate carboxyl "C incorporation into the 

 purines of DNA of several organs of growing control irradiated mice. A depres- 

 sion of about 50 per cent was observed (paper 79), thus the same as found when 

 studying the effect of irradiation on ^^p incorporation. Incorporation of i*C into 

 proteins was not found to be depressed, a shghtly increased incorporation was 

 observed. Somewhat increased i*C incorporation into the proteins following irra- 

 diation of the animal was also found by Butler et al. (1956) and in some protein 

 fractions by Richmond et al. (1957). The total tissue of the organs of exposed 

 mice investigated had a higher content of ^*C than the organs of controls (paper 81). 

 A similar result was found after administration of urethane. Muscular 

 exercise (thus enhanced metabolism) led to a decreased incorporation of i*C 

 into the tissues (paper 82). In recent years increased isotope incorporation into 

 constituents of exposed animals was observed in numerous cases (Bacq and 

 Alexander, 1955). A blockage of the incorporation of i*C into DNA will leave 

 more i*C available for entering other tissue constituents. This may explain, at 

 least to some extent, the increased rate of formation of some ^*C labelled compounds 

 in the organism exposed to irradiation. The latter may, however, also be due 

 to a cell lesion followed by an activation of enzymes. Hagen (1958) for example, 

 recently found an increase in the cathepsin activity of the thymus and spleen 

 of the irradiated mouse, and it is probable that this increase is due to a release 

 of the enzyme by the damaged cells. 



References 



Z. M. Bacq and E. Alexander (1955), Fundamentals of Badiobiology . Butter- 

 worth, London. 



J. A. V. Butler, P. Cohn and S. Crathorn (1956), P7-oc. 5th Int. Congress Radio- 

 biology. 



U. Hac4EN (1957), Strahlentherapie 106, 277. 



J. A. Richmond, M. G. Ord and L. A. Stocken (1957), Biochem. J ■ 66, 123. 



