450 



ADVENTURES IX RADIOISOTOPE RESEARCH 



due to the presence of ^^P in the cellular inorganic P fraction was smaller 

 in experiments of longer duration. 



In the consideration stated above we have disregarded the fact that 

 the amount of inorganic P extracted from the muscle is partly extra- 

 cellular P. This procedure is permissible when dealing, as above, with 

 chemical magnitudes alone in view of the fact that the amount of cel- 

 lular inorganic P is about 60 times larger than that of the extracellular 

 inorganic P of the muscle. We meet, how^ever, very different conditions 

 when considering the radioactivity of the cellular and extracellular in- 

 organic P, respectively (which is not the case in the consideration made 

 above). Due to the slow migration of the phosphate ion into the muscle 

 cells, the activity of 1 mgm extracellular inorganic P may be many hund- 

 red times larger than that of 1 mgm cellular inorganic P. 



TA.BT.E 2. — Distribution of ^^P Between the Acid 



Soluble Organic Constituents Extracted from 1 gm 



Gastrocnemius and the Inorganic Phosphate 



Extracted from 1 gm Plasma 



Table 2 contains data on the ratio of the activity of the inorganic 

 P of plasma samples and that of the acid soluble organic P fractions 

 isolated from muscle samples having the same weight as the plasma 

 samples. These ratios are stated in column 2 and indicate, as mentioned 

 above, the lower limit of the fraction of the plasma P w^hich exchanged 

 with cellular acid soluble P during the experiment. Column 3 contains 

 data on the percentage of the organic acid soluble P which was replaced 

 by plasma P during the experiment. In the course of 4 days, 8 per cent 

 was replaced. 



The amount of ^ap incorporated into the non-acid soluble P of the 

 frogs' muscle is very restricted. After the lapse of 4 days, the number 

 of 32p atoms incorporated into phosphatides makes up 2.5 per cent of 

 the amount present in the acid soluble compounds. For the ^sp incorpo- 

 rated into residual (protein) P, the corresponding figure was found 



^i^The ratio of the acid soluble P content of 1 gm muscle and 1 gm plasma was 

 found in the frog killed after 10 hours, 2 days and 4 days to be 31, 42 and 26.4 

 respectively. The variation of the above ratio is to some extent due to a variation 

 in the acid soluble P content of the plasma which was found to be 3,6, 3.6 and 

 4.8 mgm per cent respectively. 



