Malathion-induced inhibition of human plasma cholinesterase studied by the fluorescence spectroscopy method

The in vitro effect of technical grade malathion was assessed via the kinetic parameters of human plasma butyrylcholinesterase (BChE) using N-methylindoxyl acetate as a substrate for BChE. An inhibitor kinetics study demonstrated the existence of a biphasic inhibition curve, indicating high-and low-affinity binding sites of malathion. The IC 50 values as calculated from the experimental inhibition curves were 1.33 × 10−9 and 1.48 × 10−5 M for the high-and low-affinity binding sites, respectively; Hill’s analysis gave 1.29 × 10−9 and 1.38 × 10−6 M. The Cornish-Bowden plots and their secondary plots indicated that the nature of inhibition was of mixed type with the predominant competitive character of both affinity binding sites.