Carboxylesterase activity was measured in the microsomal or post-mitocondrial fractions by a continuous assay using 96-wellmicroplates. Homogenates (25 _l)were incubated with 200 _l 4-NPA as substrate (1 mM final concentration) and the buffer 50 mM phosphate buffer (pH 7.4) for 5 min at 25◦C. Formation of 4-nitrophenolate was read at 405 nm in a TECAN Infinite 200 microplate reader. Serial 4-NPA concentrations(0.03–1 mM) were assayed to estimate Vmax and Km values using the Michaelis–Menten equation, and the linearity transformation of Line weaver–Burk plot. Carboxylesterase activity was measured in triplicate and results are expressed as nmol/min/mg protein. Total protein content was determined by the Bradford’s method(1976), adapted to microplate and using the Bradford Bio-Rad Pro-tein Assay reagent and bovine serum albumin as the standard(0.05–0.5 mg/ml). The absorbance was read at 595 nm. All protein determinations were performed in triplicate.