TURNOVER OF LECITHIN, CEPHALIN AND SPHINGOMYELIN 311 



INDICATORS APPLIED IN TURNOVER MEASUREMENTS 



a) Change of the degree of unsaturatioii of fatty acids 



Since the phosphatides contain both saturated and unsaturated fatty- 

 acids, the change of the composition of the fatty acids of the organ 

 phosphatides after ingestion of cod liver oil, for example, can be utilised 

 to get information on the rate of the phosphatide turnover in the organ 

 in question. A change in the iodine number of the phospholipids extracted 

 from the liver of dogs^i^ and cats^^) after the ingestion of cod liver oil and 

 the disappearance of the changes within 24 hours and 2 to 3 days, re- 

 spectively, was observed at an early date. 



b) Incorporation of iodized fatty acids into the phosphatide molecule 



Iodized fatty acids, whether injected intravenously or given by mouth, 

 enter the phosphatides of the liver, the blood^3)and the milk^^) for example, 



c) Incorporation of elaidic acid into the phosphatide molecule 



This method was repeatedly used in the investigation of the turnover of 

 phosphatides. The rate of entrance of elaidic acid into and disappearance 

 from the phosphatides was found to be rapid in the liver and the intesti- 

 nal mucosa and comparatively slow in the muscle. The process was found 

 to be essentially complete in the liver within a day, but in the muscle 

 only after the period of many days(^). 



d) Incorporation of fatty acids, labelled by introduction of heavy hydrogen, 

 into the phosphatide molecule 



Linseed oil was deuterated and the "heavy" fat obtained fed to rats. 

 The investigation of the deuterium content of the phosphatides extracted 

 from different organs gives information on the phosphatide turnover 

 in the organ in question^. 



(1^ G. loANNOwics and E. P. Pick, Wien. Klin. Wochenschr. 23, 573 (1910), 



(2^ R. G. Sinclair, J. Biol. Chem.S2, 117 (1929). Comp. also B. G. Sinclaib, 

 Phys. Rev. 14, 351 (1934). 



^3^ C. A. Artom, Arch. int. Physiol. 36, 191 (1933); C A. Artom and G. Peretti, 

 Arch. int. Physiol. 36, 351 (1933). 



(*^ F. X. Aylward, J. H. Blackwood and J. A. B. Smith, Biochem. J. 31, 

 130 (1937). 



(5>R. Sinclair, J. Biol. Chem. 111,270 (1935); 121, 161 (1937), M. F. Kohl, 

 J. Biol. Chem. 126, 709 (1938). 



(6) B. Cavanagh and H. S. Raper, Biochem. J. 33, 17 (1939). 



