Purification, characterization of a plant esterase from red kidney bean and its feasibility for pesticide residue analysis in foods

Plant-derived esterase is a promising alternative enzyme source for pesticide residue analysis. The present study aimed to obtain purified red kidney bean esterase (RKBE), investigate its biochemical properties and application potential in pesticide residue assay. RKBE was extracted and purified by simple aqueous two-phase extraction combined with dextran gel filtration chromatography, with specific activity of 11.845 U/mg and purification fold of 18.925. SDS-PAGE revealed that RKBE has a molecular weight of 33 kDa. Preliminary structural characterization showed the amino acid sequence of RKBE was similar to that of α/β-hydrolase (ESW18998) derived from Phaseolus vulgaris with 19.5% sequence coverage, and the relative contents of β-sheet, β-turning, α-helix, and irregularly coil were 22.69%, 24.19%, 30.12%, and 23.00%, respectively. The optimal pH and temperature of RKBE were 6.5 and 40 °C. Ca2+, Mg2+, Zn2+, and low concentrations of methanol and ethanol stimulated the enzyme activity. The half-life was 138.6 days at −20 °C. Kinetic studies showed that RKBE exhibited a high affinity and catalytic activity towards 1-naphthyl acetate, with a Km of 0.277 mM and a Kcat/Km of 0.455 s−1 mM−1. Enzyme-specific inhibition assay indicated RKBE to be a carboxylesterase. Finally, pesticide susceptibility experiments confirmed that organophosphorus and carbamate pesticides exerted inhibitory effects on RKBE catalytic activity. For methamidophos, methomyl, dichlorvos, and carbaryl, the limit of detection (IC10) values in cabbage were 0.0031, 0.0045, 0.001, and 0.0065 mg/kg, respectively, suggesting that RKBE can serve as a new, widely available and cost-effective enzyme source for pesticide residual assay in foods.