EFFECT OF GLUTATHIONE DEFICIENCY ON THE ADIPOCYTE MG2-DEPENDENT PHOSPHATIDATE PHOSPHOHYDROLASE()

Previous studies from this laboratory [Jamdar S. C. and Cao W. F. (199 4) Biochem. J. 301, 793-799] show that the adipocyte Mg2+-dependent ph osphatidate phosphohydrolase (MGPPH), a major regulatory enzyme in adi pose triacylglycerol metabolism, requires an active thiol group for it s activity and perturbation of this group results in the loss of enzym e activity, Since glutathione (GSH) is important in maintaining the in tracellular thiol state, we have used GSH-deficient animals and adipoc ytes to test the possibility that intracellular GSH concentration is c ritical in controlling the MGPPH activity, The MGPPH was measured in t he presence of aqueous dispersed phosphatidate, and the release of Pi was taken as a measure of enzyme activity, The GSH deficiency in anima ls and isolated adipocytes was produced in the presence of diethylmale ate (DEM) or buthionine sulfoximine (BSO), Intraperitoneal administrat ion of BSO into animals (3 mmoles/kg) showed 10-25% reduction in the b lood and adipose GSH and 25% decline in the adipose MGPPH activity. Ho wever, DEM (0.3 ml/kg) was more effective and caused over 70% reductio n of the blood and adipose tissue GSH content and 75% decline in the a dipose MGPPH activity within 4 hr of drug administration, After 24 hr, these values returned to normal, Adipocytes incubated with 2.5 mM DEM for 60 min at 37 degrees C also showed a significant reduction in the GSH content and the MGPPH activity present in the cytosol and membran e fractions, The loss of membrane MGPPH was associated with decreased rates of triacylglycerol formation from [C-14]palmitate, Pre-incubatio n of adipocyte homogenates with I mM DEM also resulted in >90% decline in the MGPPH activity, which was preventable in the presence of GSH a nd dithiothreitol, Therefore, these studies suggest that the sulfhydry l environment offered by glutathione is critical for the maintenance o f adipocyte MGPPH activity. (C) 1997 Published by Elsevier Science Ltd .