INCREASED HEPATIC MONOACYLGLYCEROL ACYLTRANSFERASE ACTIVITY IN STREPTOZOTOCIN-INDUCED DIABETES - CHARACTERIZATION AND COMPARISON WITH ACTIVITIES FROM ADULT AND NEONATAL RAT-LIVER

Hepatic monoacylglycerol acyltransferase (EC 2.3.1.22) (MGAT) is a dev elopmentally-expressed activity associated with physiological periods characterized by high rates of lipolysis and dependence on fatty acids for energy production. During these periods, MGAT may help to retain essential fatty acids selectively. In streptozotocin-diabetes, mean MG AT-specific activity increased 11.8-fold. We characterized microsomal MGAT activity from diabetic and control adult rats, and compared these adult activities with the high neonatal activity. Compared with the a ctivity in neonatal liver, adult MGAT activity was more thermolabile, had a markedly different pH profile, and responded differently to incu bation with bovine serum albumin, phospholipids, and MnCl2. Adult diab etic MGAT activity was also stimulated 2-fold by albumin and was marke dly thermolabile, but was not inhibited by phospholipid. Diabetic MGAT activity had some properties that combined characteristics observed i n adult and neonatal microsomes: a pH dependence that was optimal at p H 7.0 but that plateaued between pH 7.0 and 9.5, and neither stimulati on nor inhibition after incubation with MnCl2. Diabetic MGAT acylated monoalkylglycerols more readily than did either the neonatal or the ad ult MGAT activities. The enhanced expression of hepatic MGAT activity in diabetes is consistent with its postulated role in retaining essent ial fatty acids during lipolysis.