NEUROPATHY TARGET ESTERASE OF HEN BRAIN - ACTIVE-SITE REACTIONS WITH 2-[OCTYL-H-3]OCTYL-4H-1,3,2-BENZODIOXAPHOSPHORIN 2-OXIDE AND 2-OCTYL-4H-1,3,2-[ARYL-H-3]BENZODIOXAPHOSPHORIN 2-OXIDE

2-Octyl-4H-1,3,2-benzodioxaphosphorin 2-oxide (octyl-BDPO) is one of t he most potent inhibitors known for neuropathy target esterase (NTE) o f hen brain with 50% inhibition at 0.2 nM. Two NTE-like proteins, i.e. , resistant to paraoxon and sensitive to mipafox, of similar to 155 an d similar to 119 kDa (designated NTE-155 and NTE-119, respectively) ar e labeled by [octyl-H-3]octyl-BDPO and separated by sodium dodecyl sul fate-polyacrylamide gel electrophoresis. Labeling with [aryl-H-3]octyl -BDPO is only similar to 15% of that with [octyl-H-3] octyl-BDPO, indi cating that the majority of the phosphorylated NTE undergoes aging wit h only a small proportion of nonaged target or intramolecular group tr ansfer (''alkylation''). NTE-155 and NTE-119 have the same kinetic con stants and maximal number of phosphorylation sites, equivalent for eac h of them to 26 fmol/mg of protein and totaling at least 0.44-1.2 mu g of NTE protein/g of brain. Structure-activity investigations involvin g If combinations of organophosphorus (OP) compounds of varied chemica l type, stereochemistry, and concentration establish an excellent corr elation (r = 0.95) between inhibition of NTE activity and protein labe ling and thereby the toxicological relevance of these assays, which eq ually implicate NTE-155 and NTE-1 19 (probably an autolysis product of NTE-155) as targets in OF-induced delayed neuropathy. [octyl-H-3]Octy l-BDPO is an improved probe for NTE in terms of its potency, reactivit y, selectivity, and the formation of H-3-labeled NTE with a stable pho sphorus-carbon bond.