ENZYMES CONCERNED WITH DIGESTION OF LIPIDS U 



are slowly hydrolyzed by the enzyme in this case; the inhibition can be 

 reversed by the addition of bile salts. 



(c) Synthetic Action of Pancreatic Lipase. Although it was early recog- 

 nized that fat is broken down to fatty acids and glycerol by the action of 

 steapsin, Pottevin, 33 in 1903, was the first to demonstrate the synthetic 

 activity of the enzyme. This investigator was able to prove a 33% com- 

 bination of oleic acid and glycerol in 50 hours at 38 °C. in the presence of 

 steapsin, while Artom and Reale 34 obtained an esterification of over 50% 

 of the starting materials when the reaction was catalyzed by fat-free pan- 

 creas powder. 



(d) Properties of Pancreatic Lipase. Pancreatic lipase, 35 although 

 soluble in water, is quite unstable in aqueous solution. It is relatively 

 stable in glycerol. It has an optimum temperature of 40°C, but retains 

 some activity at a temperature as low as 0°C. The enzyme is partially 

 destroyed by subjecting solutions for ten minutes to a temperature of 45°C, 

 while it is completely destroyed when kept at 55°C. for this time interval. 

 Steapsin is most effective in bringing about hydrolysis of triglycerides; 

 it attacks diglycerides and monoglycerides to a progressively lesser degree. 

 Of the simple triglycerides, trilaurin and triolein are the most readily 

 hydrolyzed by pancreatic lipase. Steapsin is believed to be a protein. 



(e) Specificity of Pancreatic Lipase. Fodor 36 pointed out that glycer- 

 ated homogenates of hog pancreas present a distinct difference in heat 

 stability with respect to the hydrolysis of esters composed of the shorter- 

 chain acids and monovalent alcohols, on the one hand, and that of glycerol 

 esters on the other hand. It was later shown 37 that the fraction which was 

 active in hydrolyzing glycol esters, short-chain triglycerides, and mono- 

 valent alcohols was more readily destroyed by crystalline trypsin and by 

 alkali, and more thermolabile than was the true pancreatic lipase (steapsin), 

 which acts principally on triglycerides. Thus, Fodor 37 postulates the co- 

 existence of at least two ester-hydrolyzing enzymes in pancreatic juice. 

 Hofstee 38 demonstrated two esterases (ali-esterases) in pancreatic juice 

 distinct from lipase and cholinesterase. These are called Esterase I and 

 Esterase II. Both hydrolyze valeryl salicylate, while lipase does not bring 

 about this breakdown. The action of sodium choleate was found to be 



33 H. Pottevin, Compt. rend., 186, 767-769, 1152-1155 (1903). 



34 C. Artom and L. Reale, Bull. soc. chim. biol., 18, 959-978 (1936). 



35 W. R. Bloor, Biochemistry of the Fatty Acids, Reinhold, New York, 1943. 



36 P. J. Fodor, Arch. Biochem., 25, 223-225 (1950). 



37 P. J. Fodor, Arch. Biochem., 26, 307-315 (1950). 



38 B. H. J. Hofstee, /. Biol. Chem.. 199, 357-364 (1952). 



