An in vitro comparison of rat and chicken brain neurotoxic esterase

Abstract

A systematic comparison was undertaken to characterize neurotoxic esterase (NTE) from rat and chicken brain in terms of inhibitor sensitivities, pH optima, and molecular weights. Paraoxon titration of phenyl valerate (PV)-hydrolyzing carboxylesterases showed that rat esterases were more sensitive than chicken to paraoxon inhibition at concentrations ≤1 μ m and superimposable with chicken esterases at concentrations of 2.5–1000 μ m. Mipafox titration of the paraoxon-resistant esterases at a fixed paraoxon concentration of 100 μ m (mipafox concentration: 0–1000 μ m) resulted in a mipafox I50 of 7.3 μ m for chicken brain NTE and 11.6 μ m for rat brain NTE. NTE (i.e., paraoxon-resistant, mipafox-sensitive esterase activity) comprised 80% of chicken and 60% of rat brain paraoxon-resistant activity with the specific activity of chicken brain NTE approximately twice that of rat brain NTE. The pH maxima for NTE from both species was similar showing broad, slightly alkaline optima from pH 7.9 to 8.6. [ 3H]Diisopropyl phosphorofluoridate (DFP)-labeled NTE from the brains of both species had an apparent mol wt of 160,000 measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In conclusion. NTE from both species was very similar, with the mipafox I50 for rat NTE within the range of reported values for chicken and human NTE, and the inhibitor parameters of the chicken NTE assay were applicable for the rat NTE assay.