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Yoshida M, Tomizawa M, Wu SY, Quistad GB, Casida JE: Neuropathy target esterase of hen brain: active site reactions with 2-[octyl-3H] octyl-4H-1,3,2-benzodioxaphosphorin 2-oxide and 2-octyl-4H-1,3,2-[aryl-3H] benzodioxaphosphorin 2-oxide. J Neurochem. 1995 Apr;64(4):1680-7.
2-Octyl-4H-1,3,2-benzodioxaphosphorin 2-oxide (octyl-BDPO) is one of the most potent inhibitors known for neuropathy target esterase (NTE) of hen brain with 50% inhibition at 0.2 nM. Two NTE-like proteins, i.e., resistant to paraoxon and sensitive to mipafox, of approximately 155 and approximately 119 kDa (designated NTE-155 and NTE-119, respectively) are labeled by [octyl-3H] octyl-BDPO and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Labeling with [aryl-3H] octyl-BDPO is only approximately 15% of that with [octyl-3H] octyl-BDPO, indicating that the majority of the phosphorylated NTE undergoes aging with only a small proportion of nonaged target or intramolecular group transfer ("alkylation"). NTE-155 and NTE-119 have the same kinetic constants and maximal number of phosphorylation sites, equivalent for each of them to 26 fmol/mg of protein and totaling at least 0.44-1.2 micrograms of NTE protein/g of brain. Structure-activity investigations involving 17 combinations of organophosphorus (OP) compounds of varied chemical type, stereochemistry, and concentration establish an excellent correlation (r = 0.95) between inhibition of NTE activity and protein labeling and thereby the toxicological relevance of these assays, which equally implicate NTE-155 and NTE-119 (probably an autolysis product of NTE-155) as target in OP-induced delayed neuropathy. [octyl-3H]-Octyl-BDPO is an improved probe for NTE in terms of its potency, reactivity, selectivity, and the formation of 3H-labeled NTE with a stable phosphorus-carbon bond. |
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