Kinetic studies on carboxylesterase of model nematode Caenorhabditis elegans Exposed in vitro to dichlorvos

The study was aimed to understand the kinetics of organophosphorus detoxifying enzyme carboxylesterase (EC 3.1.1.1) and to know the its sensitivity in Caenorhabditis elegans, a moist soil dwelling nematode used as model system for studying xenobiotics. Enzymatic hydrolysis of ρ-nitrophenylacetate (PNPA) showed a K_m value of 20.95 μM, V_max of 4.62 nmol min⁻¹ mg⁻¹ protein and substrate saturation of 350 μM for carboxylesterase (CaE) in vitro kinetics on exposure to dichlorvos from C. elegans. The IC₅₀ with dichlorvos, an organophosphorus compound, was 81.16 nm at excess of Km. LB plot showed the Km, V_max and V_max/K_m values of inhibited CaE: 19.57 μM, 2.88 nmol min⁻¹ mg⁻¹ protein and 0.14 min⁻¹ mg⁻¹ protein, respectively, at IC₅₀ concentration of dichlorvos. Inverse LB plot revealed the inhibition of CaE in C. elegans irreversible in presence of dichlorvos. Hence this may be used as invertebrate model to understand the other targets on exposure to dichlorovos.