TURNOVER OF LECITHIN, CEPHALIX AND SPHINGOMYELIN 341 



Besides labelled phosphate of negligible weight, 500 mgm alcohol was 

 added to the blood at the start of the experiment and 500 mgm glycine 

 after 30 min. 



When fractionating the alcoholic solution of the liver cephalin, the less 

 soluble fraction was found to show the higher specific activity amounting 



Table 30. — Specific Activity of P Fractions 



IN the Liver of a Cat 



Duration of experiment: 70 min. 



Ratio of tlic .activity of cephalin P and lecithin P = 1.67. 



to 4.47. The low lecithin activity of the plasma is, in view of the short 

 duration of the experiment, not surprising. The labelled phosphate 

 requires some time to penetrate into the liver cells, the formation of 

 labelled lecithin takes some time as well and, finally, the release of the 

 phosphatides into the plasma is far from being a momentary process. 



Survey of the results 



In the course of 4 hours, an appreciable part of the petrol-ether soluble 

 phosphatides present in the intestinal mucosa and the liver were found 

 to be renewed. This result is in conformity with that found by Artom 

 and his colleagues(i), by Chaikoff and his collaborators^^), and in this 

 laboratory<3). In Tables 31 and 32, a summary of the data obtained on 

 the renewal rate of lecithin, cephalin and sphingomyelin fractions is 

 given. In Table 32, the very different behaviour of lecithin from cephalin 

 is clearly seen. While, in the case of lecithin, the labelled percentage 

 increases more or less linearly with time, this is far from being the case 

 with cephalin. We find an almost linear increase with time in the amount 

 of labelled lecithin formed in the liver and the muscles, assuming that 

 the formation of this compound takes place inside the cells. This linearity 

 does not hold if w^e assume the formation of phosphatides to take place 

 with incorporation of extracellular P. The bulk of the labelled liver 



^1^ C. Artom, C A. Perrier, M. Santangello, G. Sarzana and E. Segre, 

 Arch. Int. Physiol. 45, 32 (1937). 



(2) B. A. Fries, S. Ruben, J. Perlman andJ. L. Chaikoff, J. Biol. Chem. 

 123, 587 (1938). 



(3)L. Hahn and G. Hevesy, Nature 144, 204 (1939). 



