Enzymic Esterification of Cholesterol in Rat Intestinal Mucosa Catalyzed by Acyl-CoA: Cholesterol Acyltransferase

Abstract

Previous work has shown CoA-dependent esterification of cholesterol in rat intestinal mucosa. Using (1-¹⁴C)oleoyl-CoA as the labeled substrate, we have proved that the esterification is catalyzed by acyl-CoA: cholesterol acyltransferase (ACAT) existing in the ‘microsomal fraction’ of the mucosal cell. The apparent K_m for oleoyl-CoA is 25 μM, the optimal pH 7.4-7.9, and the optimal concentration of albumin 10-20 mg/ml. The reaction is rectilinear for only 2 min. Increasing the microsomal cholesterol concentration by incubation with plasma from patients with familial lecithin: cholesterol acyltransferase deficiency leads to increasing ACAT activity. The ACAT was inhibited by taurocholate and by the thiol-blocking agent 5,5′-dithiobis(2-nitrobenzoic acid). The specific activity of the enzyme is high—that is, approximately 1 nmol cholesteryl oléate formed · mg microsomal protein^-1 · min^-1.

Key-words:

• Acyl-CoA: cholesterol acyltransferase (ACAT)
• cholesterol
• cholesteryl ester
• CoA
• intestines
• mucosal cell