EFFECT OF X-RAYS OX XUCLEIC ACID IX JEXSEX-SAECOMA 705 



phosphorus contains nearly the same amount of ^ap as 1 mgm of free 

 plasma phosphorus 2 hr after injection. 



Comparison of the Activity of Nucleic Acid Phosphorus with the Activity 

 of the Free Phosphorus in the Sarcoma 



It is evident from the preceding sc^ction that there is less active nucleic 

 acid formed in irradiated than in unirradiated sarcoma. It cannot be 

 concluded unconditionally from this statement, however, that the irradi- 

 ation decreases the rate of formation of nucleic acid in the sarcoma. It 

 might be thought that irradiation would make it difficult for the radio- 

 active tracer to penetrate into the sarcoma cells and that the observed 

 would be due to a decreased permeability of the cell wall to phosphate 

 under the action of the irradiation. The experiences which have been 

 accumulated from various biological systems concerning the action of 

 irradiation on permeability, and which will be reported shortly, are 

 opposed to the latter interpretation of the observed decreased forma- 

 tion of active nucleic acid in the irradiated sarcoma; we have, however, 

 set up experiments, in which the activity of the nucleic acid phosphorus 

 was compared with that of the free phosphorus in the sarcoma, in order 

 to eliminate the explanation by the effect of irradiation on the phosphate 

 permeability. The major portion of the free phosphorus in the sarcoma 

 consists of phosphorus situated within the cells; if a comparison of the 

 ratio of the activities of the nuclei acid P and the free P of the sarcoma 

 indicates a considerably smaller value in the case of the irradiated sarco- 

 ma, then this finding proves unequivocally that irradiation inhibits 

 the metabolism of nucleic acid^. 



The results of these experiments are seen in Tables 8 and 9. These 

 tables show that the radioactively labelled nucleic acid, i.e. the nucleic 

 acid formed during the 2 hr experimental period after irradiation with 

 2000 r, was about one-third the amount formed in the unirradiated 

 sarcoma. This result is supported by data obtained by a comparison 

 of the activities of nucleic acid phosphorus and free sarcoma phosphorus 

 in the fresh tissue material. (The behaviour of the necrotic tissue will 

 be discussed in the next section.) 



As has already been mentioned, the free phosphorus of the sarcoma 

 consists partly of phosphorus originating in the extracellular fluid of 

 the tissue, and this phosphorus has a specific activity (activity per mgm P) 

 which differs from that of the intracellular P. The specific activity of 



^ In our earlier experiments we have omitted a study of the activity of free 

 phosphorus in the sarcoma to enable us to use all the sarcoma tissue in obtaining 

 nucleic acid; later, however, we found it decidedly advisable to determine also 

 the specific activity of the free phosphorus in every sarcoma under investigation. 



45 Hevesy 



