TURNOVER OF LECITHIN, CEPHALIN AND SPHINGOMYELIN 



:3:3:i 



the muscles. In these fractions, both after 4 and after 12 hours cephaUn 

 and sphingomyelin are more active than lecithin. 



When looking at the results of the experiments taking one day or 

 more (see Tables 15, 16 and 22) we notice that the lecithin extracted 

 from the liver is more active than the cephalin, while the opprjsite was 

 found to be the case for the fractions secured from the brain. 



Table 19. — Renewal of Lecithin, Cephalin and Sphingomyklix 

 Rabbit V. — Weight: 2.1 kgm 

 Intravenous injection during 250 min 



<'' Turnover rate calculated on the assumption that the formation of phosphatides took place with 

 incorporation of cellular inorganic P. 



'■''> Turnover rate calculated on the assumption that the formation of phosphatides took place witli 

 incorporation of extracellular inorganic P. 



*^> Fraction extracted with cold ether. 



(5) Fraction extracted, after removal of the ether-soluble lecithin, with hot alcohol. 



Table 20. — Renewal of Lecithin and Cephalin 

 Rabbit VI. — Weight: 2.6 kgm 

 Sxibcutaneous injection during 255 nain 



Fraction 



Percentage of phosphatides renewed 

 during the esperiment 



A(0 



B(=) 



Liver lecithin . 

 Liver cephalin 



2.2 

 7.9 



I'' Turnover rate calculated on the assumption that the formation of phosphatides took place witli 

 incorporation of cellular inorganic P. 



'^' Turnover rate calculated on the assumption that the formation of phosphatides took place with 

 incorporation of extracellular inorganic P. 



Discussion 



The fact illustrated by the results described above —that in experi- 

 ments taking only a few hours, the cephalin shows a higher extent of 

 renewal than the lecithin, while, in experiments taking one day or more, 

 the opposite is the case — suggests that not all cephalin present in the 



