Purification and enzymatic properties of rat serum carboxylesterase

Rat serum carboxylesterase [carboxylic ester hydrolase, EC 3.1.1.1] was purified by ammonium sulfate precipitation, chromatography on DEAE-cellulose, QAE Sephadex A-50 and brushite, and gel filtration on Sephadex G-200. This purified enzyme was shown to be a single protein band on slab gel electrophoresis and its final specific activity was 49.5 units/mg protein. This enzyme was very sensitive to diisopropylfluorophosphate (DFP) but not to p-chloromercuribenzoate (PCMB), eserine, o-iodosobenzoate, NaF or ethylenediamine tetraacetic acid (EDTA). The pH profile of the reactions catalysed by this enzyme showed broad optimum between pH 6.0 and 8.8. The activity of purified enzyme was not affected by Ca2+, Mg2+, Mn2+, Cu2+, Zn2+, Co2+, and Cd2+ at 1 mM concentration. The molecular weight measured by gel filtration was approximately 84,000 and the isoelectric point was 4.4. The enzymatic properties were not changed by neuraminidase treatment with regard to heat stability, pH optimum, sensitivity to metal ions and inhibitors, and Km values for p-nitrophenylesters of different acyl C-chain length.