C H A P TER V 



THE OXIDATION AND METABOLISM 



OF PHOSPHOLIPIDS, AND THEIR 



HYDROLYSIS PRODUCTS 



The oxidation of the phosphoHpids is closely associated with that of 

 neutral fat. However, there are certain unique features in the metabolism 

 of these compounds which occur because of the specific nitrogen compo- 

 nents in their molecules. The behavior of choline is of particular interest 

 in the latter connection. 



1. Hydrolysis of Phospholipids 



The first step in the decomposition of all phospholipids would appear to 

 be in the hydrolysis of their molecules. As a result of such changes, fatty 

 acids, glycerol, phosphoric acid, and nitrogenous bases are ultimately set 

 free. Fatty acids and glycerol are believed to follow the same course of 

 metabolism, irrespective of whether they originate from neutral fats or 

 from phospholipids. 



The first step in the breakdown of lecithin presumal)ly involves the re- 

 moval of its two fatty acid residues, resulting in the formation of a-glyceryl- 

 phosphorylcholine (GPC). Schmidt et al.^ originally isolated this com- 

 pound from incubated beef pancreas; Schmidt and others- later demon- 

 strated the presence of GPC in aqueous extracts of several tissues, includ- 

 ing liver, while a number of investigators^"^ noted that the corresponding 

 hydrolysis product of phosphatidylethanolamine, namely glycerylphos- 

 phorylethanolamine (GPE) likewise occurs in aqueous and ethanol tissue 

 extracts. More recently Dawson^ isolated both GPC and GPE chromato- 

 graphically from rat liver, in rats which had previously been injected with 



1 G. Schmidt, B. Hershman, and S. J. Thannhauser, /. Biol. Chem., 161, 523-536 

 (1945). 



^ G. Schmidt, L. Hecht, P. Fallot, L. Greenbaum, and S. J. Thannhauser, /. Biol. 

 Chem., 197, 601-()09 (1952). 



3 P. N. Campbell and T. S. Work, Biochem. J., 60, 449-454 (1952). 



* D. M. Walker, Biochem. J., 52, 679-683 (1952). 



6 G. B. Ansell and J. M. Norman, Biochem. J., 55, 768-774 (1953). 



6 R. M. C. Dawson, Biochem. J., 57, xv (1954); 59, 5-8 (1955). 



235 



