Identification of butyrylcholinesterase adducts after inhibition with isomalathion using mass spectrometry: difference in mechanism between (1R)- and (1S)-stereoisomers.

摘要: Previous kinetic studies found that butyrylcholinesterase (BChE) inhibited by (1R)-isomalathions readily reactivated, while enzyme inactivated (1S)-isomers did not. This study tested the hypothesis (1R)- and inhibit BChE different mechanisms, yielding distinct adducts identifiable peptide mass mapping with matrix-assisted laser desorption/ionization time-of-flight spectrometry (MALDI–TOF–MS). Equine (EBChE) was to <10% of control activity each isomer isomalathion reference compound isoparathion methyl. Control treated digested trypsin, peptides were fractionated HPLC. Separated unseparated analyzed MALDI–TOF–MS. Identity an organophosphorus adduct confirmed fragmentation using postsource decay analysis. EBChE or (S)-isoparathion methyl reactivated after oxime treatment 30–40% recovered. Enzyme (1S)-isomalathions (R)-isoparathion recovered <2% <5% activity, respectively, treatment. MALDI–TOF–MS analysis revealed inhibition (R)- yielded O,S-dimethyl phosphate adducts. produced only O-methyl adduct. modified either enantiomer as well. The results indicate proceeds loss diethyl thiosuccinate, but inactivation occurs thiomethyl primary leaving group followed rapid expulsion thiosuccinate yield aged enzyme. Furthermore, data suggest aging via SN2 process thiomethyl.