4 I. GENERAL CHARACTERISTICS AND CLASSIFICATION 



(2) Compound or Conjugate Lipids 

 This group is distinguished by the presence in the molecule of products 

 other than fatty acids and alcohol. In some cases no alcohol is present 

 and the fatty acids are combined in a peptide-like linkage rather than as 

 esters. 



a. Phospholipids or Phosphatides. The former term is most generally 

 employed in the United States while the latter one is favored in English 

 and German literature. This sub-group is characterized by the fact that 

 it contains a phosphoric acid molecule as an integral part of the structure. 



(a) Lecithin. This consists of glycerol, two fatty acid residues (one 

 saturated and one unsaturated), phosphoric acid, and choline (HOCHo- 

 CH2N(CH3)3-OH). 



(6) Cephalin. There are at least three, and possibly more, types of 

 compounds which belong in this group. These are the following : 



a'. Phosphatidyl Ethanolamine : This is the classical kephalin which 

 hydrolyzes to glycerol, two fatty acids (one saturated and one unsaturated), 

 phosphoric acid, and ethanolamine. The latter nitrogenous base appears in 

 the molecule in place of the choline in lecithin. 



b'. Phosphatidyl Serine: This is a product recently separated from 

 brain cephalin by Folch^ which hydrolyzes to glycerol, two fatty acids, 

 phosphoric acid, and serine. The latter amino acid is attached to H3PO4 

 through the hydroxy! group. 



c'. Phosphatidyl Inositol or Lipositol: This is a phosphatide recently 

 isolated from brain^'^° and from soybean oil,^' and shown to contain inosi- 

 tol, fatty acids, galactose, tartaric acid, phosphoric acid, and ethanolamine 

 in an undefined combination.'' 



(c) Sphingomyelin. This contains a nitrogenous base, sphingosine 

 (CH3(CH2)i2CH:CHCHOHCHOHCH2NH2), a single fatty acid, phos- 

 phoric acid, and choline, but no glycerol. 



(d) Phosphatidic Acids. These are compounds which have been pre- 

 pared from plant sources and which are similar to lecithin minus the cho- 

 line. Components isolated on hydrolysis are fatty acids (saturated and 

 unsaturated), glycerol, phosphoric acid, and calcium. '^ 



b. Cerebrosides. These compounds contain a carbohydrate as well as 

 a fat molecule, but no phosphoric acid or glycerol. 



(a) GaJactolipids. These compounds, found chiefly in the brain, hy- 



drolyze to a fatty acid (usually containing 24 carbon atoms), sphingosine, 



and galactose. 



« J. Folch, /. Biol. Chem., 139, 973-974 (1941). 



" J. Folch and D. W. Woolley, /. Biol. Chem., 143, 963-964 (1942). 



'0 J. Folch, J. Biol. Chem., I46, 35-44 (1942). 



11 E. Klenk and R. Sakai, Z. phijsiol. Chem., 258, 33-38 (1939). 



12 D. W. Woolley, /. Biol. Chem., U7. 581-591 (1943). 



i» A. C. Chibnall and H. J. Channon, Biochem. J., 23, 176-184 (1929). 



