Ashani_1995_J.Biol.Chem_270_6370

Reference

Title : Amino acid residues controlling reactivation of organophosphonyl conjugates of acetylcholinesterase by mono- and bisquaternary oximes - Ashani_1995_J.Biol.Chem_270_6370
Author(s) : Ashani Y , Radic Z , Tsigelny I , Vellom DC , Pickering NA , Quinn DM , Doctor BP , Taylor P
Ref : Journal of Biological Chemistry , 270 :6370 , 1995
Abstract : Single and multiple site mutants of recombinant mouse acetylcholinesterase (rMoAChE) were inhibited with racemic 7-(methylethoxyphosphinyloxy)-1-methylquinolinium iodide (MEPQ) and the resulting mixture of two enantiomers, CH3PR,S(O)(OC2H5)-AChE(EMPR,S-AChE), were subjected to reactivation with 2-(hydroxyiminomethyl)-1-methylpyridinium methanesulfonate (P2S) and 1-(2'-hydroxyiminomethyl-1'-pyridinium)-3-(4"-carbamoyl-1"- pyridinium)-2-oxapropane dichloride (HI-6). Kinetic analysis of the reactivation profiles revealed biphasic behavior with an approximate 1:1 ratio of two presumed reactivatable enantiomeric components. Equilibrium dissociation and kinetic rate constants for reactivation of site-specific mutant enzymes were compared with those obtained for wild-type rMoAChE, tissue-derived Torpedo AChE and human plasma butyrylcholinesterase. Substitution of key amino acid residues at the entrance to the active-site gorge (Trp-286, Tyr-124, Tyr-72, and Asp-74) had a greater influence on the reactivation kinetics of the bisquaternary reactivator HI-6 compared with the monoquaternary reactivator P2S. Replacement of Phe-295 by Leu enhanced reactivation by HI-6 but not by P2S. Of residues forming the choline-binding subsite, the E202Q mutation had a dominant influence where reactivation by both oximes was decreased 16- to 33-fold. Residues Trp-86 and Tyr-337 in this subsite showed little involvement. These kinetic findings, together with energy minimization of the oxime complex with the phosphonylated enzyme, provide a model for differences in the reactivation potencies of P2S and HI-6. The two kinetic components of oxime reactivation of MEPQ-inhibited AChEs arise from the chirality of O-ethyl methylphosphonyl moieties conjugated with Ser-203 and may be attributable to the relative stability of the phosphonyl oxygen of the two enantiomers in the oxyanion hole.
ESTHER : Ashani_1995_J.Biol.Chem_270_6370
PubMedSearch : Ashani_1995_J.Biol.Chem_270_6370
PubMedID: 7890775

Related information

Inhibitor MEPQ
Reactivator MEPQHI-6P2s~contrathion

Citations formats

Ashani Y, Radic Z, Tsigelny I, Vellom DC, Pickering NA, Quinn DM, Doctor BP, Taylor P (1995)
Amino acid residues controlling reactivation of organophosphonyl conjugates of acetylcholinesterase by mono- and bisquaternary oximes
Journal of Biological Chemistry 270 :6370

Ashani Y, Radic Z, Tsigelny I, Vellom DC, Pickering NA, Quinn DM, Doctor BP, Taylor P (1995)
Journal of Biological Chemistry 270 :6370