In enzymology, a triacylglycerol---sterol O-acyltransferase () is an enzyme that catalyzes the chemical reaction triacylglycerol + a 3beta-hydroxysterol diacylglycerol + a 3beta-hydroxysterol ester Thus, the two substrates of this enzyme are triacylglycerol and 3beta-hydroxysterol, whereas its two products are diacylglycerol and 3beta-hydroxysterol ester. This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is triacylglycerol:3beta-hydroxysterol O-acyltransferase. This enzyme is also called triacylglycerol:sterol acyltransferase. References EC 2.3.1 Enzymes of unknown structure