Cholesterol esterases: IV. Cholesterol esterase of rat intestinal mucosa.

Nieft and Deuel (1, 2) found that in rat liver and intestinal mucosa two different opposing systems were responsible for the synthesis and hydrolysis of cholesterol esters. The esterifying system required the presence of phosphate ion and a fatty acid source. The hydrolytic system consisted of at least two factors and its activity was accentuated by soy bean lecithin. While their extracts were prepared in a standard manner and were of constant concentration, they report that it was impossible to tell beforehand which would be the predominant reaction in any given extract. Esterification by extracts of intestinal mucosa could be demonstrated only when the animals had been fed a diet containing 1 per cent lanolin or 1 per cent cholesterol for 2 or 3 weeks previous to sacrifice. Extracts of the intestines of such animals initially exhibited only esterifying activity. However, dialysis against distilled water for 21 hours inactivated the esterifying system and then the hydrolytic system could be demonstrated. Recent papers (3-5) from this laboratory have reported procedures for studying the esterifying and hydrolyzing cholesterol e&erase systems and the occurrence and characteristics of both systems in pancreatin and dog serum. The properties of the enzyme in pancreatin appeared to be favorable for activity in the lumen of the small intestine; namely, optimum pH in the range of 6 to 7 and activity in the presence of bile salts.’ In view of the papers by Mueller (6), Frolicher and Stillmann (7), and Schramm and Wolff (8), who have suggested that either hydrolysis or esterification or both are important in the absorption of cholesterol, it seemed desirable to investigate further the occurrence of cholesterol esterase in the intestinal mucosa. Accordingly, extracts of rat intestine were