ENZYMES CONCERNED WITH DIGESTION OF LIPIDS O 



Desuuelle 3 and Favager 4 discussed, in a comprehensive manner, the enzy- 

 matic hydrolysis of triglycerides. 



(1) Lipases 



a. Gastric Lipase. There would appear to be little doubt that fat may, 

 under some conditions, undergo hydrolysis in the stomach. However, it 

 is still a moot question whether this hydrolysis of fat is to be traced to a 

 fat-splitting enzyme produced by the stomach mucosa, or whether the 

 lipolytic action observed in this organ is due to pancreatic lipase which has 

 been regurgitated. 



Although Magendie, 5 as early as 1825, reported changes of fat in the 

 pyloric region of the stomach, most of the work of later investigators gave 

 opposite results. However, Hull and Keeton 6 found that gastric juice, 

 obtained from dogs with Pavlov accessory stomachs, did possess appreci- 

 able lipolytic activity when the secretion was neutral or when it was neu- 

 tralized as soon as produced. The failure of earlier workers to obtain posi- 

 tive results was thus explained as due to the hyperacidity of the gastric 

 juice. The later work of Willstatter and Memmen 7 offers considerable 

 evidence that gastric lipase does actually exist. According to these 

 workers, gastric lipase is secreted in active form and not as a zymogen; 

 it occurs in greater concentration in the cardiac than in the fundic end of 

 the stomach, but the extracts are from 40 to 600 times weaker than those 

 obtained by similar means from the pancreas. The optimum pH is on the 

 alkaline side of neutrality, as in the case of pancreatic lipase; in fact, 

 Willstatter and Memmen 7 could not demonstrate any qualitative differences 

 between the above two lipolytic enzymes. 



In any event, the pH usually existing in the stomach is unfavorable, not 

 only for the emulsification of fat but also for the action of gastric lipase. 

 Such highly emulsified fats as those in egg yolk and milk may undergo 

 some hydrolysis; the extent of this reaction is somewhat increased in the 

 infant stomach, where the prevailing acidity more nearly approximates the 

 optimum pH of both gastric and pancreatic lipases. Everett 8 states that, 

 even in the infant, less than 5% of fat is hydrolyzed in the stomach. 



3 P. Desuuelle, Bull. soc. chim. bioi, 33, 909-923 (1951). 



4 P. Favager, Bull. soc. chim. biol., 33, 924-960 (1951). 



6 F. Magendie, Prtcis elementaire de physiologie, Vol. II, 2nd ed., Mequignon-Marvis, 

 Paris, 1825, p. 142; cited from W. R. Bloor, Biochemistry of the Fatty Acids, Reinhold, 

 New York, 1943, p. 112. 



6 M. Hull and R. W. Keeton, J. Biol. Chem., 32, 127-140 (1917). 



7 R. Willstatter and F. Memmen, Z. physiol. Chem., 133, 247-259 (1924). 



8 M. R. Everett, Medical Biochemistry, 2nd ed., P. B. Hoeber, New York and London, 

 1910, p. 211. 



