Chromatographic Discrimination of Soluble Neuropathy Target Esterase Isoenzymes and Related Phenyl Valerate Esterases from Chicken Brain, Spinal Cord, and Sciatic Nerve

Abstract: Neuropathy target esterase (NTE) activity is operatively defined in this work as the phenyl valerate esterase (PVase) activity resistant to 40 µM paraoxon but sensitive to 250 µM mipafox. Gel filtration chromatography with Sephacryl S‐300 of the soluble fraction from spinal cord showed two PVase peaks containing NTE activity (S‐NTE1 and S‐NTE2). The titration curve corresponding to inhibition by mipafox was studied over the 1–250 µM range, in the presence of 40 µM paraoxon. The data revealed that S‐NTE1 and S‐NTE2 have different sensitivities to mipafox with I50 (30 min) values of 1.7 and 19 µM, respectively. This was similar to the pattern observed in the soluble fraction from sciatic nerve with two components (Vo peak, or S‐NTE1; and 100‐K peak, or S‐NTE2) with different sensitivity to mipafox. However, in the brain soluble fraction, only the high‐molecular‐mass (>700‐kDa) peak or S‐NTE1 was obtained. It showed an I50 of 5.2 µM in the mipafox inhibition curve. The chromatographic profile was different on changing the pH in the subcellular fractionation. When the homogenized tissue was centrifuged at pH 6.8, the Vo peak activity decreased in the soluble fraction from these nerve tissues. This suggests that the Vo peak could be related to materials partly solubilized from membranes at higher pH. The chromatographic pattern and mipafox sensitivity suggest that the different tissues have a different NTE isoform composition. S‐NTE2 should be a different entity than S‐NTE1 and particulate NTE. The potential role of soluble forms in the mechanism of initiation or promotion of neuropathy due to organophosphorus remain unknown.

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