Molecular pharmacology of manoalide. Inactivation of bee venom phospholipase A2.

The marine natural product manoalide (MLD) was shown to directly inactivate bee venom phospholipase A2 (PLA2). Inactivation was pH dependent (maximum inactivation occurred at pH 8.0), time dependent and concentration dependent. The IC50 was estimated at 0.05 microM and virtually complete inactivation of the enzyme occurred at 4.0 microM. The time-dependent loss of PLA2 activity suggested that inactivation does not follow typical Michaelis-Menten kinetics. Reversibility was studied directly by dilution and dialysis; both methods were ineffective in dissociating the MLD-PLA2 complex. A kinetic plot of initial velocity (v) versus [PLA2] supported our hypothesis that MLD apparently inactivates bee venom PLA2 by an irreversible mechanism.