354 



ADVENTURES IN RADIOISOTOPE RESEARCH 



obtained, followed by 2 ml 10 per cent ammonium molybdate solution. The inorga- 

 nic P was precipitated overnight; the filtrate was then hydrolyzed for 20 minutes 

 at 100°C and cooled. The precipitate contained the labile P of ATP. This was 

 dissolved in 15 ml 5 per cent NHg and its P precipitated as magnesium ammonium 

 salt. The precipitate was dissolved in 0.1 n HCl, an aliquot being used in the 

 eolorimetric essay, while another was precipitated as magnesium ammonium salt 

 and reserved for the radioactive measurements. 



Percentage Turnover of Liver Phosphatides 



The lower limit of the percentage turnover of liver phosphatides 

 per hour, which is calculated from the percentage ratio of the speci- 

 fic activities of the liver phosphatide P at the end of the 2 hour-experi- 

 ment and the mean value of the orthophosphate P during the experi- 

 ment (which was by 10 per cent less than the end value) and divided 

 by 2, is given in column 2 of Table 2, while column 3 contains values 



Table 2. 



Lower Limit of the Percentage Turnover per 



HotTR OF THE Phosphatides of the Rat Liver. ATP Pj 3 Scale 



Age of rats 



Percentage turnover per liour 



AVithout considering 

 repeated renewal 



Considering 

 repeated renewal 



4 d 



10 d 



14 d 



30 d 



10 d 



1.5 year(i) 



<'' Calculated from inorganic P value. 



12.1 ± 1.2 



9.9 ± 1.0 



10.0 ± 1.0 



9.6 ± 1.0 



7.7 ±0.8 

 5.7 + 0.6 



12.7 ± 1.3 



10.4 ± LI 



10.5 ± l.l 

 10.1 ± 1.0 



8.1 +0.8 

 6.0 + 0.6 



corrected for the repeated renewal of phosphatide molecules during the 

 experiment. The correction is obtained by calculating the percentage 

 ratio of the average specific activities of the phosphatide P and the 

 orthophosphate P during the experiment. The average ratio of the spe- 

 cific activity of the phosphatide P was taken to be half of the end value 

 (cf. footnote, p. 353). The turnover rate is seen to decrease with the age 

 of the rats, the percentage turnover rate of the phosphatides of 1.5 

 year-old rats being only about half of that obeserved in 4 day-old rats. 



In Table 3 the percentage turnover calculated by comparing the speci- 

 fic activity of the phosphatide P with that of the inorganic P is shown. 



BoLLMAN et al. (1948) found the percentage turnover per hour to 

 be about 5. From the fact that their rats weighed 200 gm we have to 

 conclude that the animals investigated were fully grown rats for which 

 we arrive at a corresponding figure of 8 to 6. Furthermore, we have to 



