238 V. OXIDATION AND METABOLISM OF PHOSPHOLIPIDS 



Fujino^i used pig spleen as the source of the enz3^me preparation. It was 

 suggested that sphingomyehns and cerebrosides are so closely related that 

 they can interchange through the intermediate ceramides. It would appear 

 that phosphorylcholine may be an intermediate in the hydrolysis of 

 sphingomyelin, while it is not believed to function in this capacity in the 

 case of lecithins and cephalins. However, the conditions are different in 

 the former case because glycerol is not present in the sphingomyelin mole- 

 cule. 



2. The Degradation of Phospholipids by Means Other Than by 



Hydrolysis 



O'Connell and Stotz'- demonstrated that, when hydrolecithin from beef 

 brain or beef lung was oxidized by rat liver homogenates in the presence of 

 ATP, no acetoacetate originated, in spite of the fact that these end-products 

 occur when free fatty acids are the substrates. According to Harper et al.,^^ 

 the rate of utilization of intravenously-injected phospholipid is propor- 

 tional to the plasma P level in both normal and diabetic dogs. Although 

 the absolute utilization of plasma phospholipid was slightly lower in the 

 diabetic group than in the normal animals, the proportion of plasma phos- 

 pholipid utilized per hour by the diabetic group was significantly higher. 

 The administration of either insulin or sugar did not increase phospholipid 

 utilization by diabetic dogs; however, it was increased when raw pancreas 

 was given. ^' 



The utilization of phospholipid in brain and liver is catalyzed by iron 

 compounds, especially if ascorbic acid is added. ^^ In the brain, only the 

 cephalin fraction undergoes oxidation under these conditions. Although 

 several investigators^*- ^^ have reported that the turnover of brain lipids 

 (unsaponifiable fraction) is comparatively slow, Sperry" found that a de- 

 crease in extractable phosphorus occurred during a four-hour incubation 

 period as the result of a cleavage of phospholipids in brain tissue. Stanley^^ 

 reported the formation of acid-soluble phosphate and of inositol when ceph- 

 alin fractions of brain were treated with homogenates of fresh adult guinea 



12 P. W. O'Connell and E. Stotz, Proc. Soc. Exptl. Biol. Med., 70, 675-677 (1949). 



13 P. V. Harper, Jr., W. B. Neal, Jr., and J. R. Rogers, Proc. Soc. Exptl. Biol. Med., 

 68, 363-369 (1948). 



1^ K. A. Elliott and B. Libet, /. Biol. Chem., 152, 617-626 (1944). 

 15 L. Hahn and G. Hevesv, Skand. Arch. Physiol., 77, 148-157 (1937). 

 i« W. M. Sperry, H. Waelsch, and V. A. Stovanoff, /. Biol. Chem., 135, 281-290, 

 291-296(1940). 



1' W. M. Sperry, /. Biol. Chem., 170, 675-686 (1947). 

 i« G. H. S. Stanley, Biochetn. J., 49, iv-v (1951). 



