EFFECT OF X-RAYS ON NUCLEIC ACID IN JENSEN-SARCOMA 70^ 



time, then the percentage of newly formed nucleic acid molecules is 

 not 2 per cent but 4 per cent. The change in the specific activity of the 

 free phosphorus in the sarcoma cells does not follow a simple propor- 

 tionality; initially it is practically equal to zero for a few minutes, 

 since the absorption of the injected P and its penetration into the extra- 

 cellular and intracellular volumes require time. On the other hand, the 

 specific activity rises only slightly with time in the last phase of the 

 experiment; when equilibrium between the activity of the plasma 

 (extracellular) P and the cellular P is almost attained, then the specific 

 activity of the sarcoma P changes only slightly with time. In a number 

 of cases has there been not only equalization of the specific activities 

 of the sarcoma and liver phosphorus after two hours, but the former 

 has indeed exceeded the latter. The cause of this process is that the 

 activity of the plasma P reaches a maximum within the first ^2 1^^ 

 after subcutanous injection and then decreases gradually. Very active 

 P penetrates into the cells from the highly active plasma; this P is, of 

 course, again replaced by newly arriving less active plasma P, but the 

 equalization of activity between the sarcoma P and plasma P takes 

 place more slowly than the changes in the plasma activity, and thus is 

 explained the fact that sarcoma P more active than plasma P can be 

 encountered after 2 hr. In the above discussions it must be borne in 

 mind that the free phosphorus of the sarcoma cells has not only the 

 ability to enter and escape through the cell wall, but also has various 

 chances of incorporation into the organic phosphorus-containing mole- 

 cules of the sarcoma cells. After the entry of the very active plasma P 

 there is a correspondingly rapid entry of P into adenosine triphosphate, 

 hexose monophosphate and similar molecules, which then serve as a 

 storage space of the highly active P. If this phosphorus flows back 

 again into the plasma, which has meanwhile become impoverished, 

 then the loss in activity of the free sarcoma P will be compensated by 

 an escape of strongly active P from the storage space and, therefore, 

 this process contributes to maintaining the higher level of activity of 

 the free sarcoma P. In certain conditions the activity of the sarcoma P 

 can indeed undergo a decline, instead of a nonlinear increase with time, 

 in the later phases of the experiment. By multiplying the final value 

 of the specific activity of the sarcoma P by about 1.5, we should obtain 

 the average value for the free sarcoma P during the course of the experi- 

 ment and of the raw material serving for the formation of the active 

 nucleic acid. We then have to multiply by 1.5 the value obtained for 

 t he ratio of the activities of 1 mgm of nucleic acid P and 1 mgm of sarcoma 

 P in order to obtain the value of the percentage increase of nucleic acid 

 in the sarcoma in the course of 2 hr. This value therefore amounts to 

 about 3 per cent of the total quantity of nucleic acid, or on the average 

 0.26 mgni'/gm of sarcoma. 



