MICROSOMAL DIACYLGLYCEROL ACYLTRANSFERASE IN RAT PAROTID AND SUBMANDIBULAR GLANDS - ACYLATION OF 1,2-DIOLEOYL-SN-GLYCEROL DISPERSED WITH PHOSPHOLIPIDS

In order to investigate microsomal diacylglycerol acyltransferase acti vity, ethanol or several detergents have been used as a dispersing age nt for water-insoluble substrates. However, ethanol acyltransferase in terferes with the activity of this enzyme, and detergents inhibit it. We examined the properties of microsomal diacylglycerol acyltransferas e in rat salivary glands without detergents or organic solvents. 1,2-D ioleoyl-sn-glycerol (1,2-diolein) was dispersed by sonication. The act ivity was measured as the formation rate of [C-14]triglyceride using [ 1-C-14]palmitoyl-CoA as an acyl-donor. The reaction was dependent on t he microsomal protein and 1,2-diolein at least up to 145 mu g/ml and 3 .6 mM, respectively. The specific activities were 3.91 +/- 0.57 and 3. 80 +/- 0.77 nmol/min per mg protein (SEM, n = 4) in the parotid and su bmandibular glands, respectively. They were 12- to 20-fold higher than the activities in liver, brain and spleen, and two orders of magnitud e higher than that assayed with microsomal endogenous diacylglycerol. Adding tissue phospholipids to 1,2-diolein suspension reduced the conc entration of 1,2-diolein required for the maximal velocity. A similar, but reduced, effect was induced by egg yolk phosphatidylcholine in pl ace of the tissue phospholipids. The level of activity was recovered b y adding another phospholipid class to the phosphatidylcholine. The re sults suggested that the physical condition of the substrate diacylgly cerol affects diacylglycerol acyltransferase activity in rat salivary gland microsomes. Copyright (C) 1996 Elsevier Science Ltd