THE LECITHINS 421 



(8) Enzymic Hydrolysis of the Lecithins 



i\Io8t lipases presumably act on lecithin as well as on fats. Thiele^"- 

 found an enzyme in the blood which is able to hydi-olyze lecithin but not 

 fat. Such an enzj'me would be considered to be an esterase but not a 

 lipase. Porter/"* after examination of the enzymes in many tissues, con- 

 cluded that lipases and lecithinases act independently. Moreover, four 

 different tj'pes of enzymes are now known which are believed to produce 

 specific effects on each of the ester linkages in the lecithin molecule.^"* 

 These enzymes may be listed as follows : 



a. Lecithinase A. This libcraii'S only one fatty acid from the molecule, with the 

 formation of lysolecithin. 



b. Lecithinase B. This enzyme iiydrolyzes off both fatty acids from the lecithin 

 molecule. 



c. Lecithinase C. This enzyme splits only the choline from lecithin, by rupturing 

 the ester linkage between choline and phosphoric acid. 



d. Lecithinase D. This is a true glycerophosphatase which acts on the ester linkage 

 between phosphoric acid and glycerol, producing phosphorylcholine and a diglyceride. 



Considerable work has been done on the undifferentiated lecithinases, 

 using the production of soluble phosphate as an index of their activity. 

 j^jj-ig.105 found that the optimum pE. was 7.5, and that such enzymes were 

 widely distributed in nature. The highest content was present in kidney, 

 \\-hile a decreasing activit^y was observed in various tissues in the following 

 order: small intestine, spleen, liver, testes, pancreas, large intestine, brain, 

 o\airy, bone, suprarenals, lung, blood vessels, cardiac muscle, and skeletal 

 muscle. In later investigations, King ^"^ found that lecithinase had an 

 optimum activity at body temperature, while artificial hydrolecithins were 

 also acted upon as rapidly as was the parent lecithin. However, the 

 synthetic lecithin of Grim^ and distearyl phosphate, were acted upon much 

 more slowly than was the natural product, and no pH optimum was noted. 

 The behavior was so divergent that it leads one to question the identity 

 of the synthetic and the natural lecithins. On the other hand, the phos- 

 phate is set free from lysolecithin at about twice the rate, and also from 

 l)romolecithin at a greatly accelerated speed as compared with that of 

 lecithin. The effect of pK on hydrolysis of natural and synthetic lecithin 

 is shovMi in Figure 1. 



More recent work has been concerned with the activity of specific 

 lecithinases. Lecithinase A, or "phospholipase" as termed by Fairbairn,*"^ 

 which is present in the venom of many poisonous snakes such as the cobra 



•OS F. A. Thiele, Biochem. /., 7, 275-286, 287-296 (1913). 



>»3 A. E. Porter, Biochem. J., 10, 52.3-533 (1916). 



10^ A. Contardi and A. Ercoli, Biochem. Z., 261, 275-302 (1933). 



105 E. J. King, Biochem. J., 25, 799-811 (1931). 



!"« E. J. King, Biochem. J., 28, 476-481 (1934). 



10' D. Fairbairn, ./. Biol. Chem., 157, 633-644 (1945). 



