Phosphatidic acid, lysophosphatidic acid, and lipid A are inhibitors of glycosylphosphatidylinositol-specific phospholipase D. Specific inhibition of a phospholipase by product analogues?
Previous work has suggested that the glycosylphosphatidylinositol-specific 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 [3H]myristate-labeled variant surface glycoprotein dispersed in Nonidet P-40 as substrate. Inhibition of GPI-PLD by PAs (IC50 approximately 1 microM) was relatively independent of the length or degree of unsaturation of the fatty acyl chains. It was also observed that lysophosphatidic acid and several natural and synthetic lipid A preparations were inhibitory in the same concentration 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 the inhibitor. The inhibitory lipids did not affect substrate availability 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 indicated that inhibition was specific for lipids containing a phosphomonoester group. The data suggest that inhibition is due to a direct interaction between PA (or lipid A) and the GPI-PLD rather than an indirect effect on the substrate particle.
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Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons of Columbia University, New York, New York 10032.
Huang
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D000818:Animals; D002417:Cattle; D005227:Fatty Acids / Q000378:metabolism; D020404:Glycerophospholipids; D006801:Humans; D008050:Lipid A / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism*; D010739:Phospholipase D / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013379:Substrate Specificity
D005227:Fatty Acids; D020404:Glycerophospholipids; D008050:Lipid A; D008246:Lysophospholipids; D010712:Phosphatidic Acids; C025602:dimyristoylphosphatidic acid; D010739:Phospholipase D; C065017:glycoprotein phospholipase D