Enzymic esterification of cholesterol in rat intestinal mucosa catalyzed by acyl-CoA: cholesterol acyltransferase.

Previous work has shown CoA-dependent esterification of cholesterol in rat intestinal mucosa. Using (1-(14)C)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 microM, 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 oleate formed x mg microsomal protein(-1) x min(-1).