Acyl-CoA:cholesterol acyltransferase in human small intestine: its activity and some properties of the enzymic reaction.
Esterification of endogenous cholesterol in human small intestinal mucosa by acyl-CoA:cholesterol acyltransferase (ACAT, EC 2.3.1.26) was studied using [1-14C]oleoyl-CoA as substrate. The reaction was linear for 2 min only. The esterification of cholesterol was stimulated by albumin, but this effect was dependent on the oleoyl-CoA concentration. When the albumin concentration was 5 g/liter, maximal esterification was obtained with 35 microM oleoyl-CoA. The pH optimum was 7.2-7.8. The ACAT specific activity was highest in microsomal preparations from jejunum (0.21 +/- 0.19 (n = 18) nmol cholesteryl oleate . mg microsomal protein-1 . min-1), and lower in proximal duodenum and distal ileum. Whole homogenates of biopsies had about 1/4 of the activity of the corresponding microsomal preparation. Microsomal preparations from jejunum contained acyl-CoA hydrolase (EC 3.1.2.2) which under the prevailing conditions had a maximal activity of 4.4 nmol oleate formed . microsomal protein-1 . min-1. The high activity of intestinal ACAT in man renders it possible that this enzyme plays a role in cholesterol absorption.
D000214:Acyl Coenzyme A / Q000378:metabolism; D000217:Acyltransferases / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology; D007421:Intestine, Small / Q000201:enzymology*; D007700:Kinetics; D009829:Oleic Acids / Q000378:metabolism; D010170:Palmitoyl-CoA Hydrolase / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D002785:Sterol O-Acyltransferase / Q000378:metabolism*; D014018:Tissue Distribution
D000214:Acyl Coenzyme A; D002788:Cholesterol Esters; D005230:Fatty Acids, Nonesterified; D009829:Oleic Acids; C017585:oleoyl-coenzyme A; D012710:Serum Albumin, Bovine; C014409:cholesteryl oleate; D000217:Acyltransferases; D002785:Sterol O-Acyltransferase; D010170:Palmitoyl-CoA Hydrolase