ENZYMES CONCERNED WITH DIGESTION OP LIPIDS 23 



and Wolff 137 reported that a pancreatic esterase was able to esterify not 

 only cholesterol but also dehydroandrosterone and dihydrocholesterol with 

 equal rapidity. Three plant sterols, namely sitosterol, stigmasterol, and 

 ergosterol, were also esterified by this enzyme, but at a slower rate than that 

 of the animal sterols. Swell and Treadwell, 138 using as a substrate choles- 

 terol and oleic acid, demonstrated that the esterifying enzyme in pancreas 

 required bile and a source of fatty acids for activity. It was equally active 

 in the presence of phosphate or of citrate buffer. Optimum pH was 6.2; 

 the enzyme was inactivated by heating for 15 minutes at 65 °C. Swell 139 

 reported that the action of pancreatic cholesterol esterase was augmented 

 by the bile salts in the following order: taurocholate > cholate > glyco- 

 cholate > desoxycholate > lithocholate. The first three bile salts were the 

 most active, which is interpreted to mean that the — OH groups are the 

 active ones in bile salts. Since cholate with glycine or taurine was no more 

 active than the cholate by itself, it is suggested that sodium taurocholate 

 and sodium glycocholate do not undergo splitting but rather function as a 

 unit. Maximum activity was noted when one bile salt molecule was pres- 

 ent with one cholesterol and one oleic acid molecule. 



The esterifying and hydrolyzing systems occur side by side in the blood, 

 in the liver, in the pancreas, and in the intestinal wall; however, it is not 

 believed that these two systems are aspects of a reversible process. 



b. Lecithinases. Although most lipases presumably are able to act on 

 lecithins as well as on neutral fat, Thiele 140 was the first to report the pres- 

 ence of an enzyme in blood capable of hydrolyzing lecithin but which did 

 not act on neutral fat. After examination of the enzymes in many tissues, 

 Porter 141 concluded that lecithinases and lipases act independently. Con- 

 tardi and Ercoli, 142 in 1933, postulated that four types of lecithinases exist, 

 depending upon the particular bonds which are attacked. 



(a) Lecithinase A. This enzyme liberates one fatty acid from lecithin 

 with the formation of a lysolecithin. 142 Lecithinase A has been reported in 

 cobra venom 143 " 145 ; it splits a single unsaturated acid from the lecithin 

 molecule. According to Hanahan and collaborators, 146 lecithinase A from 



137 G. Schramm and W. Wolff, Z. physiol. Chem., 263, 73-77 (1940). 



138 L. Swell and C. R. Treadwell, J. Biol. Chem., 182, 479-487 (1950). 



139 L. Swell, Federation Proc, 12, 278 (1953). 



140 F. H. Thiele, Biochem. J., 7, 275-286, 287-296 (1913). 



141 A. E. Porter, Biochem. J., 10, 523-533 (1916). 



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



143 P. Kyes, Berl. klin. Wochschr., 40, 956-959, 982-984 (1903). 



144 C. Delezenne and S. Ledebt, Compt. rend., 155, 1101-1103 (1912). 



145 C. Delezenne and E. Fourneau, Bull. soc. chim. France, 15, 421-434 (1914) 



146 D. J. Hanahan, L. D. Turner, and M. A. Rodbell, Federation Proc, 12, 214 (1953). 



