Catalytic characteristics of plant-esterase from wheat flour.

A plant-esterase extracted from wheat flour and purified with a PEG1000/NaH(2)PO(4) aqueous two-phase system was characterized for its catalytic characteristics. The optimal condition for plant-esterase to catalyze 1-naphthyl acetate was at 30°C, pH 6.5. It kept stability at 20°C during 120 min and at pH 5.5 during 60 h. The effects of metal ions, chemical modification reagents and pesticides on plant-esterase activity were investigated. It was found that Ba(2+) and Pb(2+) at concentrations of 20 mM significantly inhibited the activity of plant-esterase while Mg(2+), Ca(2+) and Fe(2+) at the same concentration enhanced the enzyme activity. Chemical modification reagents significantly influenced the activity of plant-esterase. Particularly, PMSF (4.5 mM) and N-bromosuccinimide (11 mM) inhibited by 5.40-19.87% of the enzyme activity. It is implied that serine and tryptophan are related to the enzyme activity. Plant-esterase were displayed concentration-dependent inhibition by dichlorvos, carbofuran and carbendazim (IC50 = 0.31-63.12 ppm). All these results indicated that catalytic efficiency of plant-esterase strongly depends on reaction conditions, activity effectors and amino acid residues at the active site. It makes meaningful guidance on further design of sensing material in monitoring pesticides.