Studies on cholesterol esterases of the small intestine and pancreas of rats

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Abstract
The hydrolytic and synthetic activities of rat pancreas and intestine for cholesteryl oleate were optimum at pH 8.6 and 6/1 respectively. The hydrolytic and synthetic activities differ in their sensitivity to mercuric chloride, quinine hydrochloride, sodium arsenite, atoxyl, zinc chloride and copper sulphate. The esterification of [beta]-sitosterol by the intestine and pancreas was 86 and 35% of cholesterol esterification respectively. The cholesterol esterases of the pancreas and small intestine of rats are different Tween 20 inhibited the hydrolytic more than the synthetic activity and deoxycholate inhibited the synthetic but not the hydrolytic activity of the pancreas. The hydrolytic and synthetic activities of the pancreas for cholesteryl oleate were separated by absorption on calcium phosphate gel followed by elution. Vitamin A esterases were also separated from the cholesterol esterases. Inactlvation obtained by incubation at pH 8,6 for 25 min. could be prevented by sodium taurocholate. Deoxycholate, at high concentrations, afforded partial protection, whereas de-hydrocholate was inactive. After exhaustive dialysis of the enzymes treated with sodium taurocholate the enzymes were not inactivated by incubation. From a study of the relative efficiency of the different bile salts, and their structure in the protection of the enzymes against in-activatlon, it is concluded that the hydroxyl group at position C-7 on the phenanthrene ring is essential.