INACTIVATION OF BEE VENOM PHOSPHOLIPASE A(2) BY A SESQUITERPENE FURANOIC ACID MARINE NATURAL PRODUCT

A sesquiterpene furanoic acid (SFA) marine natural product isolated fr om soft corals of the genus Sinularia (Bowden et al., Aust J Chem 36: 371-376, 1983) was found to inactivate bee venom phospholipase A(2) (b vPLA(2), EC 3.1.1.4) in vitro. In this study, we characterized the kin etics of inactivation of bvPLA(2) by this compound. The apparent IC50, value was 0.5 mu M, and the inactivation of bvPLA(2) was time depende nt. The drug-enzyme binding appeared to be of a non-competitive, high- affinity nature that was irreversible by aqueous dialysis. The inactiv ation was prevented by the simultaneous addition of excess lysophospha tidylcholine (lysoPC) during the initial binding step, suggesting that modification of the enzyme by SFA occurs at or near the substrate bin ding site. Activation of bvPLA(2) was observed with lysoPC addition at concentrations equimolar to bvPLA(2) and higher. Saturation of activa tion occurred at concentrations greater than 10 mu M lysoPC, and prein cubation of bvPLA(2) with 100 mu M lysoPC did not inhibit the enzyme. Analysis of the post-incubation mixture of SFA-inhibited enzyme in the presence of lysoPC revealed the presence of unaltered enzyme exhibiti ng typical Michaelis-Menten kinetics. The significance of these observ ations is discussed in light of the recent discussion by Ortiz on the manoalide binding site on bvPLA(2) (Ortiz et al., J Med Chem 36: 1866- 1879, 1993).