Properties of monoglycerol acyltransferase in rat adipocytes

Previous studies by Coleman and Haynes (1986, J. Biol. Chem. 261, 224-228) indicated the presence of two different tissue specific monoacylglycerol acyltransferases (MGAT) in intestinal mucosa and suckling rat liver. The evidence was based upon the differential responses of these two isoenzymes to various treatments including, the effects of temperature, proteolysis, protein modification reagents, detergents, and divalent cations. In the present investigation, we have used some of these criteria to determine the identity of adipose enzyme with the MGAT present in liver and intestinal microsomes. The properties of adipose and intestinal enzymes were similar in several respects, but differed from the liver enzyme. This suggests the possibility that MGAT activities from adipose and intestine may be mediated by the same enzyme protein, whereas the liver MGAT may be a separate isoenzyme as proposed earlier. The most distinguishing feature of the liver enzyme was its ability to sustain both high temperature (52 degrees C) and resist proteolysis. However, when disrupted microsomal preparations were used, the liver enzyme was both thermolabile and protease sensitive, as observed for the intestinal and adipose MGAT. Possibly, the location of liver MGAT within the membranes may be responsible for such unique properties of liver MGAT.