EFFECT OF X-RAYS ON NUCLEIC ACID IN JENSEN-SARCOMA 7 1 9 



work of SvEDBERG and Brohult^^\- or degradation of plasma proteins 

 into particles of lower molecular weight. 



In addition to the cleavage fragments from high polymers, a series 

 of other constituents are found in irradiated tissue such as, for example, 

 nascent oxygen which permits Ihe formation of hydrogen peroxide and 

 other oxidation products. 



The X-rays have no selective affinity for one or other iyipe of molecule 

 in the tissue; any atom in the irradiated tissue has approximately the 

 same probability of being ionized as any other atom; it can be assessed 

 at 4xl0~" for irradiation with a dose of 1 r.^^^ It is possible that the 

 X-rays and the ions liberated by the radiation act directly upon a con- 

 stituent required for the synthesis of nucleic acid, e. g. by cleaving such 

 a molecule; it is not less probable, however, that the entry of noxious 

 products into the synthetic phase leading to cell division is the determin- 

 ing step. 



Suniniary 



Rats with Jensen -sarcoma are injected subcutaneously with a radioactivelj^ 

 labelled phosphate solution; after the passage of 2 hr desoxjribonucleic acid 

 of the sarcoma is isolated. 



If the nucleic acid is found to bo radioactive it follows that nucleic acid mole- 

 cules have been synthesized in the sarcoma during the course of the experiment.^ 



A comparison of the activity of 1 mgm of nucleic acid P with the activity from 

 1 mgm of free sarcoma P makes it possible to determine the amount of newly formed 

 nucleic acid. 



The nucleic acid molecules formed in the course of 2 hr amount to 2 — 3 per 

 cent of the total nucleic acid content, which on the average constitutes 9 mgm/gm 

 of sarcoma. 



The irradiation of the sarcoma with 1000 international roentgen units and 

 even with a dose of 450 r or less, causes a decrease of the foimation of 

 nucleic acid, in the great majority of cases, to an average of half to one-third 

 of the value found in an unirradiated sarcoma. Individual sarcomas (five of forty 

 five), which presumably are particularly resistant to radiation, exhibit normal 

 formation of nucleic acid even after irradiation. 



The method described permits detection of the effect of radiation on the 

 growth of the sarcoma by a chemical method directly after irradiation. 



The nucleic acid formation in necrotic sarcoma tissue amounts to about 

 half to one-quarter of that found in fresh tissue. The free phosphate of the sarcoma 

 cells is replaced more slowly by plasma phosphate in necrotic tissue than in fresh 

 tissue, but in the necrotic tissue the bulk of the free phosphate originallj^ 

 present in the sarcoma cells is also replaced in a period of 2 hr. 



iTh. Svedberg and S. Brohult, Nature 143, 938 (1938). 

 1 P. Jordan, Radiologica 2, 25 (1938). 



