The Enzymology of Cholesterol Esterification

Abstract

Formation of cholesteryl esters are catalyzed by several different enzymes, the most important are acyl-CoA: cholesterol acyltransferase, lecithin: cholesterol acyltransferase, and cholesterol ester hydrolase. Because the substrates of these enzymes are mostly water-insoluble and bound to biomembranes, and because the products are transferred to other compartments, the determinations of these enzymes are very difficult. The problems concerning lecithin: cholesterol acyltransferase are discussed in more detail. The formation of cholesteryl ester in plasma is dependent both on the enzyme and on the availability of substrates. It is almost impossible to separate these two factors in an enzyme assay. Using radioactive cholesterol in the assay presupposes a known degree of isotopic equilibrium. This is difficult, especially in abnormal sera. Assay for the activity of lecithin: cholesterol acyltransfer is not a routine method, and should be performed only in connection with other measurements of lipid metabolism.