Figure 3

Effects of deet on cholinesterase enzymatic activities. a) and b) Inhibition of D. melanogaster (a) and Human (b) acetylcholinesterases (AChEs) by deet. Note the dose-dependant decrease of ATCh hydrolysis by AChE following deet application. [ATCh]: Acetylthiocholine concentration in micromole per liter; v/[Et] specific activity in s-1. c) Inhibition of human (Hu) butyrylcholinesterase by deet. As previously observed with ATCh, deet is also capable of strongly decreasing the BTCh hydrolysis by human BChE. [BTCh]: butyrylthiocholine concentration in micromole per liter; v/[Et] specific activity in s-1. d and e) Dose-dependant effect of deet on Drosophila (d) and Human (e) AChE carbamoylation rates by propoxur (carbamate). The curves clearly show the strong reduction of the second order rate constant (ki) for the carbamoylation of HuAChE by propoxur in presence of deet. At high concentration (10 mM), protection of AChE by deet is total. f) Accommodation and binding of deet inside the active site of Human AChE. The picture was created by VMD, a Visual Molecular Dynamics program. After QMMM relaxation of the complex between HuAChE and deet molecule, the latter was accommodated in a tetrahedral adduct conformation. Minimal adaptation of the side chains of adjacent residues in the active side of HuAChE suggests that the accommodation of deet in a position favourable for enzymatic hydrolysis is possible.