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

• Published in: Journal of neurochemistry Vol. 64; no. 4; p. 1680
• Main Authors: Yoshida, M, Tomizawa, M, Wu, S Y, Quistad, G B, Casida, J E
• Format: Journal Article
• Language: English
• Published: England 01.04.1995
• Subjects: Animals; Brain - enzymology; Carboxylic Ester Hydrolases - antagonists & inhibitors; Carboxylic Ester Hydrolases - chemistry; Carboxylic Ester Hydrolases - metabolism; Chickens; Female; Isomerism; Membranes - enzymology; Molecular Weight; Organophosphorus Compounds - metabolism; Organophosphorus Compounds - pharmacology; Osmolar Concentration; Solubility
• ISSN: 0022-3042
• DOI: 10.1046/j.1471-4159.1995.64041680.x

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.