LIPIDES 



89 



and a-glycerophosphoric acid. The ester linkage existing between 

 glycerol and phosphoric acid is exceptionally strong and can be broken 

 only by prolonged boiling with a strong acid. 



Lecithins are hydrolyzed in living tissues by means of certain 

 enzymes called lecithinases. There are apparently a number of differ- 

 ent lecithinases, each one capable of splitting the lecithin molecule 

 at a different linkage. For example, lecithinase A removes one fatty 

 acid residue and yields a product referred to as a lysolecithin. Certain 

 snakes, such as the cobra, produce a venom containing lecithinase A. 

 When the venom is injected into a victim, lysolecithin is produced and 

 is poisonous owing to its ability to dissolve (hemolyze) red blood cells. 

 Following is the structure for a typical a-lysolecithin: 



CH.— OH 



O 



CH— O— C— R 



O 



CH,— O— P— O— CH2— CH2 



-N(CH3)3 



+ 



o- 



a-lysok'cilhin 



Lecithinase B is responsible for the cleavage of both fatty acid resi- 

 dues from the lecithin molecule, thus producing a-glyccrophosphoryl 

 choline. Still another lecithinase is capable of removing the nitrog- 

 enous base, choline, from lecithin to form a compound known as a 

 phosphatidic acid. Such phosphatidic acids usually exist in living 

 tissues as metallic salts. 



O 



CHoOH 



CHOH 



O 



CH2— O— C— R 



O 



II 

 CHO— C— Ri 



O 



CHo— O— P— O— CHo— CH2— N(CH3)3 CH2— O— P— OH 



o- 



a-glycerophosphoryl choline 



o- 



a-phosphatidic acid 



Cephalins, which occur in many living tissues but are particularly 



