BIOCHEMICAL-PROPERTIES AND POSSIBLE TOXICOLOGICAL SIGNIFICANCE OF VARIOUS FORMS OF NTE

NTE (neuropathy target esterase) is considered to be the target for or ganophosphorus-induced delayed polyneuropathy and is operationally mea sured by radiolabelling or by determining its esteratic activity as th e paraoxon-resistant mipafox-sensitive phosphorylable site(s). From el ectrophoresis and density gradient centrifugation using radiolabelling techniques, several phosphorylable sites have been described in hen b rain that are paraoxon-resistant mipafox-sensitive; however, only the majority electrophoresis band (155 kDa) shows properties related with the aging reaction. Kinetic criteria have also suggested two component s of brain NTE (NTE(A) and NTE(B)). Most brain NTE is recovered in the particulate microsomal fraction and only about 1% in soluble fraction . In sciatic nerve about 50%/50% activity is recovered as soluble (S-N TE) or particulate (P-NTE) forms. A similar distribution were observed in hen, cat, rat and young chick. The fixed time inhibition curves sh ow that P-NTE is more sensitive to mipafox, DFP and hexyl-DCP than S-N TE, while the reverse is true for methamidophos. P-NTE fits properly t o one sensitive component while S-NTE fits better to two sensitive com ponent models, except in the case of methamidophos. In vivo, significa nt differences in the inhibition or P- and S-NTE by mipafox were found only when using low non-neuropathic dosing. The possible significance of different NTE forms are discussed.