11] Diacylglycerol acyltransferase and monoacylglycerol acyltransferase from liver and intestine

Abstract

The acylation of diacylglycerol catalyzed by the diacylglycerol acyltransferase is the only enzyme reaction unique to triacylglycerol synthesis. This reaction lies at the diacylglycerol branch point of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol synthesis. In most tissues, the major pathway for the biosynthesis of the diacylglycerol substrate proceeds from the acylation of glycerol 3-phosphate. In intestine and liver, however, the monoacylglycerol pathway provides an alternate route for diacylglycerol synthesis. 2-monoacylglycerol—produced by the action of gastric and pancreatic lipases on dietary triacylglycerol—enters the intestinal mucosa where monoacylglycerol acyltransferase plays a major role in resynthesizing triacylglycerol. In the liver of certain species, monoacylglycerol acyltransferase activity is high during early development; however, neither its specific role in liver nor the source of the monoacylglycerol substrate is known. Both diacylglycerol acyltransferase and monoacylglycerol acyltransferase are intrinsic membrane proteins whose active sites face the cytosolic surface of the endoplasmic reticulum.