Monoacylglycerol acyltransferase activity in the rat liver plasmalemma fractions

Bile canalicular membranes and plasma membranes free of bile canalicular membranes were prepared from rat livers and their lipolytic activities were measured. Both preparations catalyzed hydrolysis and transacylation when monoacylglycerol and phosphatidylethanolamine were used as substrates. The specific enzymatic activity in the plasmalemma free of bile canalicular membranes was slightly higher than that in bile canalicular membranes. Neither preparation attacked the triacylglycerol of chylomicra, which indicates the lack of a lipoprotein lipase. Heparin and CaCl₂ stimulated the activities in both preparations. On the basis of these data, we suggest that monoacylglycerol acyltransferase can serve two distinct roles in the liver cell, depending upon the mumbrane fraction of association.