Activated Ketones as Inhibitors of Intracellular Ca2+-Dependent and Ca2+-Independent Phospholipase A2

Abstract

Studies are reported on two different types of activated ketones as inhibitors of two important intracellular phospholipase A2s (PLA2): the group IV 85 kDa Ca2+-dependent phospholipase A2 (cPLA2) and the P388D1 Ca2+-independent phospholipase A2 (iPLA2). In a mixed micelle assay, we observed that the reaction progress curve of cPLA2 in the presence of a trifluoromethyl ketone (TFMK) is linear at pH 7.4, while at pH 9.0 it is nonlinear and slows with time. An investigation of this discrepancy demonstrated that the TFMKs are slow, tight-binding inhibitors of the cPLA2 at both pH's, that the rate of dissociation of the enzyme−inhibitor complex is the same at both pH's, but that the rate of association of enzyme and inhibitor is slower at pH 7.4 than at pH 9.0. A novel group of activated ketone inhibitors has been synthesized that contain a fatty acyl tricarbonyl. These compounds also inhibit the cPLA2 in the mixed micelle assay. The inhibition of cPLA2 by the tricarbonyls is readily reversible upon dilution ...