PHOSPHATIDIC-ACID, LYSOPHOSPHATIDIC ACID, AND LIPID-A ARE INHIBITORS OF GLYCOSYLPHOSPHATIDYLINOSITOL-SPECIFIC PHOSPHOLIPASE-D - SPECIFIC-INHIBITION OF A PHOSPHOLIPASE BY PRODUCT ANALOGS

Previous work has suggested that the glycosylphosphatidylinositol-spec ific phospholipase D (GPI-PLD) purified from bovine serum is inhibited by phosphatidic acid (PA). In this study we report on the specificity and mechanism of this phenomenon using [H-3]myristate-labeled variant surface glycoprotein dispersed in Nonidet P-40 as substrate. Inhibiti on of GPI-PLD by PAs (IC50 approximately 1 muM) was relatively indepen dent of the length or degree of unsaturation of the fatty acyl chains. It was also observed that lysophosphatidic acid and several natural a nd synthetic lipid A preparations were inhibitory in the same concentr ation range. The inhibitory potency of PA, lysophosphatidic acid, and lipid A was dependent on the detergent concentration in the assay but in all cases this was in a large (i.e. >100-fold) molar excess over th e inhibitor. The inhibitory lipids did not affect substrate availabili ty nor did they reduce hydrolysis of variant surface glycoprotein by a bacterial phosphatidylinositol-specific phospholipase C. Studies with a wide range of other lipids, detergents, and phosphate esters indica ted that inhibition was specific for lipids containing a phosphomonoes ter group. The data suggest that inhibition is due to a direct interac tion between PA (or lipid A) and the GPI-PLD rather than an indirect e ffect on the substrate particle.