Inhibition of rice bran lipase by azadirachtin from Azadirachta indica

BACKGROUND: Chemical constituents of the neem tree are extensively explored; the major component present in the tree is
azadirachtin. Azadirachtin, a tetranortriterpenoid, is remarkable for its chemical complexity and for its biological activity. This
study, for the first time, has provided information on the interaction and inhibition of rice bran lipase (RBL) by azadirachtin. RBL,
an esterase, is a versatile enzyme that catalyzes the hydrolysis of ester linkages, primarily in neutral lipids such as triglycerides.
RESULTS: The catalytic activity of RBL in the presence of azadirachtin has been investigated. There was a decrease in enzyme
activity relative to the control at all concentrations tested. At 1mmol L−1 concentration of azadirachtin the enzyme loses 84%
of its activity. The kinetics of inhibition of RBL by azadirachtin are competitive in nature. From analysis of the kinetic data the
inhibition constant Ki is found to be 0.14mmol. Fluorescence measurements showed a gradual decrease in emission intensity;
a red shift in emission maximummay be attributed to perturbation of the aromatic residues. Far-ultraviolet circular dichroism
results showedminor conformational changes.
CONCLUSION: The results suggest that azadirachtin specifically inhibits and binds to RBL in bringing about inhibition with
minor structural alteration. This inactivation of RBL by azadirachtin can be utilized to prevent oxidation of RBLwith an ultimate
goal of exploiting the potential of the plant source for producing edible-grade oil from rice bran using a natural molecule at
very low concentration.