248 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



It has been generally assumed, until recently, that lecithin and other 

 phospholipids are hydrolyzed in the gastrointestinal tract, and are ab- 

 sorbed in the form of the hydrolytic products. It is believed that these 

 fragments are reconstituted into the phospholipid molecule in the in- 

 testinal mucosa. 



The mechanism of the hydrolysis of lecithins in the small intestine is 

 not certain. As early as 1877, Bokay 1 proposed that lecithin was broken 

 down to fatty acids, choline (referred to as "neurine"), and glycerophos- 

 phate; the latter ester was believed to be split into glycerol and phos- 

 phoric acid in the intestine, by phosphatase. 2 Abderhalden and Paffrath 

 demonstrated that choline originated when lecithin was allowed to re- 

 main in intestinal segments of the rabbit in vitro, 3 as well as when lecithin 

 solutions were incubated with intestinal juice. 4 It was proved by Kahane 

 and Levy 6 that lecithinase B is present in rat intestine. This enzyme 

 splits the two fatty acid residues from the lecithin molecule, leaving glyc- 

 erylphosphorylcholine. Schmidt et al. 6 have likewise shown that lecithin 

 disappears during the autolysis of minced rat intestine, concomitantly 

 with the appearance of glycerylphosphorylcholine. In earlier work, 

 Schmidt, Hershman, and Thannhauser 7 had reported that duodenal juice 

 was without effect on lecithin or cephalin, although intestinal mucosa was 

 capable of hydrolyzing these phospholipids. It has likewise been re- 

 ported that alkaline phosphatase has the ability to convert glycerylphos- 

 phorylcholine into glycerol, phosphoric acid, and choline. 7 Lecithinase 

 B has been found in beef pancreas. 6 - 7 A review of the earlier literature is 

 given by Belfanti, Contardi, and Ercoli. 8 The mechanism for the hy- 

 drolysis of the lecithin molecule is pictured on the following page. 



According to Le Breton and Pantaleon, 9 an enzyme in the pancreatic 

 juice of dogs which is probably distinct from steapsin or other pancreatic 

 lipase liberates fatty acids from lecithin and from cephalin. 



There are several reports in the literature which demonstrate a more or 

 less significant increase in lecithin in the lymph, following administration 



1 A. Bokay, Z. physiol. Chem., 1, 157-164 (1877). 



2 P. Grosser and J. Husler, Biochem. Z., 39, 1-5 (1912). 



3 E. Abderhalden and H. Paffrath, Fermentforschung, 8, 284-293 (1926). 



4 E. Abderhalden and H. Paffrath, Fermentforschung, 8, 294-298 (1926). 



5 E. Kahane and J. Levy, Compt. rend., 219, 431-433 (1944). 



G. Schmidt, L. Hecht, and S. J. Thannhauser; cited by S. J. Thannhauser and 

 G. Schmidt, Physiol. Revs., 26, 274-317 (1946), p. 310. 



7 G. Schmidt, B. Hershman, and S. J. Thannhauser, J. Biol. Chem., 161, 523-536 

 (1945). 



8 S. Belfanti, A. Contardi, and A. Ercoli, Ergeb. Enzymforsch., 5, 213-232 (1936). 



9 E. Le Breton and J. Pantaleon, Arch. sci. physiol, 1, 63-80 (1947). 



