Partial purification and properties of a soil enzyme that degrades the insecticide malathion

Abstract

1. 1. An unusually stable esterase which catalyzes the hydrolysis of malathion to its monoacid was extreacted from irradiation-sterilized soil and non-irradiated soil with 0.2 M NaOH and partially purified by MnCl 2 treatment, (NH 4) 2SO 4 precipitation, dialysis and ion exchange chromatography. A 240-g sample of Chehalis clay loam yielded 28 mg of final preparation. It contained 9.8 mg of protein and hydrolyzed 31 μmoles of malathion in 4 h at pH 7.0 and 37°. Lineweaver-Burk plots obtained for two concentrations of the enzyme gave identical K m values of 2.12·10 −4 M. The enzyme was optimally active around pH 7.0. The enzyme was very stable, being denatured only at temperatures above 70° and by 24-h exposures at pH < 2.0 and pH > 10.0. Lyophilization partially destroyed the activity but no loss of activity occurred during extended storage of enzyme solutions at 4° or frozen at − 10°. 2. 2. When partially purified enzyme was applied to soil, activity was detected for the duration of the experimental period (8 weeks). Its existence as a stable, cell-free soil enzyme is postulated from experimental evidence based on the persistence and adsorptive characteristics of the partially purified enzyme in soil. This esterase should be an excellent tool for investigating enzymatic biological transformations in soil.