90 



GENERAL BIOCHEMISTRY 



abundant in brain, differ in structure from the lecithins only in the 

 type of nitrogenous base bound to the phosphoric acid residue. Instead 

 of choline, cephalins have been found to contain either ethanolamine 

 (HOCHoCHoNHo) or serine (HO— CH2— CH— COQ-). In order to 



NH3+ 



distinguish between the two types of cephalins the names phosphatidyl 



ethanolamine and phosphatidyl serine are used. 



O 



11 

 CH2— O— C— R 



O 



II 

 GH— O— C— Ri 



O 



CH2— O— P— O— CH2— CH2NH3 



1 



o- 



o-phosphatidyl ethanolamine 



o 



CH2— O— C— R 



o 



CH— O— C— Ri 



O 



O 



II / 



CH2— O— P— O— CH2— CH— C— OH 



o- 



NH3 

 + 



a-phosphatidyl serine 



The two types of cephalins may be separated from each other by 

 making use of the fact that the phosphatidyl ethanolamines are 

 alcohol soluble whereas the phosphatidyl serines are alcohol insoluble. 



The third group of phospholipides mentioned in a previous para- 

 graph are the ether- and acetone-insoluble sphingomyelins. Although 

 originally isolated from brain tissue, these compounds have been 

 shown to occur in many organs of the body, as well as in blood and 

 milk. On complete hydrolysis, sphingomyelins yield an amino alcohol 



