Suicide-inhibitory bifunctionally linked substrates (SIBLINKS) as phospholipase A2 inhibitors

Novel phospholipids that function as mechanismbased inhibitors for phospholipase At (PLA2) are described.PLA2-catalyzed hydrolysis of the sn-2 ester of these suicide-inhibitory bifunctionally linked substrates (SIBLINKS) followed by a cyclization reaction generates a cyclic anhydride at the active site of the enzyme which leads to inhibition.Structure/activity relationships for the SIBLINKS substituents in the sn-1 and sn-2 position are delineated.Time courses and efficiency of SIBLINKS inhibition are reported and compared for extracellular PLAzs obtained from Nuju nuja naju, porcine pancreas, bee venom, Crotalus utrox and Crotalus adamanteus.SIBLINKS-inhibited PLA2s cannot process either monomeric or micellar substrates consistent with inhibition at the catalytic site.Some SIBLINKS efficiently inactivate 1 mol of N .nuja naju and C. adamanteus PLA2/6-10 mol of SIB-LINKS hydrolyzed.Inhibition of N .nuju nuju PLA2 can be reversed by hydroxylamine, suggesting that a tyrosine residue is acylated.Phospholipase A, (PLA2)' comprises a ubiquitous set of intracellular and extracellular hydrolytic enzymes that hydrolyze the sn-2 ester of phospholipids; the extracellular PLAzs are relatively well characterized, particularly those secreted by the pancreas or contained in various venoms (1, 2).The extracellular enzymes are low molecular mass (about 13,000 daltons) thermally stable proteins with an absolute dependence on Ca2+ for activity.These enzymes have been grouped into at least three major classes based on their different disulfide bond patterns (3,4).Certain phospholipases liberate arachidonic acid, which is the precursor of prostaglandins, leukotrienes, thromboxane, prostacyclin, and HETEs (5).Interest in modulators or inhibitors of PLA, activity has been stimulated by the finding that a plethora of biological responses are induced by these metabolic products (5).Since phospholipase A, has been postulated to play a central role in septic shock, rheumatoid arthritis, and the production of inflammatory eicosanoids in general, developing inhibitors of this enzyme is important (5,6).* A gift of financial support was provided by Eastman Kodak.The costs of