A novel type of phospholipase A2 inhibitor, thielocin A1 beta, and mechanism of action.

Thielocin A1 beta, a novel phospholipase A2 inhibitor, was isolated from Thielavia terricola RF-143. It inhibited various phospholipase A2s in a dose-dependent manner. Among these, group II phospholipase A2 from rat was most sensitive to thielocin A1 beta (IC50 = 0.0033 microM). The inhibition of phospholipase A2 by thielocin A1 beta was independent of Ca2+ and substrate concentration. In addition, the inhibition of rat group II phospholipase A2 was noncompetitive (Ki = 0.0068 microM) and reversible. Furthermore, thielocin A1 beta quenched the relative fluorescent intensity of Naja naja venom phospholipase A2 and in a dose-dependent manner; 50% quench was noted with a molar ratio of thielocin A1 beta/enzyme of 2.2. These observations indicated that inhibition of phospholipase A2 by thielocin A1 beta may result from direct interaction with the enzyme.