2.2. Carboxylesterase activityCarboxylesterase activity was measured in the microsomal orpost-mitocondrial fractions by a continuous assay using 96-wellmicroplates (Hosokawa and Satoh, 2002). Homogenates (25 l)were incubated with 200 l 4-NPA as substrate (1 mM final concen-tration) and the buffer 50 mM phosphate buffer (pH 7.4) for 5 minat 25◦C. Formation of 4-nitrophenolate was read at 405 nm in aTECAN Infinite 200 microplate reader. Serial 4-NPA concentrations(0.03–1 mM) were assayed to estimate Vmaxand Kmvalues usingthe Michaelis–Menten equation, and the linearity transformationof Lineweaver–Burk plot. Carboxylesterase activity was measuredin 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 proteindeterminations were performed in triplicate.