318 



ADVENTURES IN RADIOISOTOPE RESEARCH 



activity of the tissue inorganic P and the plasma inorganic P at diffe- 

 rent intervals. The change of the specific activity of the tissue inorganic 

 P is seen in Table 1, that of the plasma inorganic P is discussed on 

 page 315. 



Table 1. — Specific Activity of the Organ 



Inorganic P as Percentage of that of the 



Plasma Inorganic P 



<') In spite of all precautions taken, some creatine P may have been split off before the extraction of the 

 inorganic P. The creatine P being, in experiments of short duration, less active than the inorganic P, such 

 a decomposition may partly be responsible for the low value obtained in the experiment taking 100 min only. 



") Comp. p. 336 



It is of interest to remark that, in the case of the kidneys, after the 

 lapse of 100 min an almost proportional partition of ^^p between plasma 

 and cellular P is reached. When investigating, after 4 hours, the inorganic 

 P of the marrow of the kidney, which makes out only a minor part 

 of the total inorganic P of the kidney, the specific activity was found 

 to be only 48 per cent of that of the plasma. 



CELLULAR AND EXTRA -CELLULAR FORMATION OF 



PHOSPHATIDES 



The turnover rates recorded in the fourth column of Tables 3 to 9 are 

 calculated on the assumption that the formation of phosphatide molecu- 

 les takes place inside the cells with participation of cellular inorganic P. 

 Let us assume for a moment that the formation of phosphatide molecules 

 takes place on the cell wall facing the interspaces. Then, not the cellular 

 but the extracellular phosphate radicals^!) would enter the newly formed 

 phosphatide molecules. As the specific activity of the extracellular 

 inorganic P is often much higher than that of the cellular inorganic P, 

 in the last mentioned case more active P atoms would take part in the 

 synthetic process than in the first mentioned one. A high activity of 

 the newly formed phosphatide would then not indicate such a high 



(1) From this view-point, it is without any significance whether the phosphate 

 radical is directly incorporated into the phosphatide molecule or through inter- 

 mediary stages. 



