Modulation of neurotoxic esterase activity in vitro by phospholipids

Neurotoxic esterase (NTE), the proposed molecular site for the initiation of organophosphorus-induced delayed neuropathy, is a membrane-associated enzyme. NTE activity was solubilized from chicken brain microsomal membranes with the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1- propanesulfonate and partially separated from other solubilized hen brain esterases by DEAE-Sephacel anion-exchange chromatography using stepwise increases in salt concentration; however, there was poor recovery of NTE activity and only a slight increase in NTE specific activity. NTE activity in the "high salt" fraction (i.e., the NTE-enriched fraction) was markedly activated by a heat-stable factor(s) present in other fractions eluted from the column. This activating factor was extracted with organic solvents, suggesting that it may be lipid. In a related study, purified phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine were also found to activate the partially separated NTE activity in a concentration-dependent manner while phosphatidyl-inositol was found to inhibit the same partially separated NTE fraction in a concentration-dependent manner. The results suggest that lipids may modulate NTE activity and that the loss of lipid cofactors during chromatographic separations may underlie some of the difficulties encountered in isolation of active NTE.