Journal article
Identification of Butyrylcholinesterase Adducts after Inhibition with Isomalathion Using Mass Spectrometry: Difference in Mechanism between (1R)- and (1S)-Stereoisomers
Toxicology and applied pharmacology, Vol.176(2), pp.73-80
10/15/2001
DOI: 10.1006/taap.2001.9279
PMID: 11601883
Abstract
Previous kinetic studies found that butyrylcholinesterase (BChE) inhibited by (1R)-isomalathions readily reactivated, while enzyme inactivated by (1S)-isomers did not. This study tested the hypothesis that (1R)- and (1S)-isomers inhibit BChE by different mechanisms, yielding distinct adducts identifiable by peptide mass mapping with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF–MS). Equine BChE (EBChE) was inhibited to <10% of control activity with each isomer of isomalathion and the reference compound isoparathion methyl. Control and treated enzyme was digested with trypsin, and peptides were fractionated with HPLC. Separated and unseparated peptides were analyzed with MALDI–TOF–MS. Identity of an organophosphorus peptide adduct was confirmed by fragmentation using postsource decay analysis. EBChE inhibited by (1R)-isomalathions or (S)-isoparathion methyl readily reactivated after oxime treatment with 30–40% activity recovered. Enzyme inactivated by (1S)-isomalathions or (R)-isoparathion methyl recovered <2% and <5% activity, respectively, after oxime treatment. MALDI–TOF–MS analysis revealed that inhibition of EBChE by (1R)-isomalathions and (R)- or (S)-isoparathion methyl yielded O,S-dimethyl phosphate adducts. Enzyme inactivated by (1S)-isomalathions produced only O-methyl phosphate adduct. EBChE modified by (1R)-isomalathions or either enantiomer of isoparathion methyl yielded an O-methyl phosphate adduct as well. The results indicate that EBChE inhibition by (1R)-isomalathions proceeds with loss of diethyl thiosuccinate, but inactivation by (1S)-isomers occurs with loss of thiomethyl as the primary leaving group followed by rapid expulsion of diethyl thiosuccinate to yield an aged enzyme. Furthermore, the data suggest that aging of the O,S-dimethyl phosphate adduct occurs via an SN2 process with loss of thiomethyl.
Details
- Title: Subtitle
- Identification of Butyrylcholinesterase Adducts after Inhibition with Isomalathion Using Mass Spectrometry: Difference in Mechanism between (1R)- and (1S)-Stereoisomers
- Creators
- Jonathan A Doorn - Toxicology Program, The University of Michigan, Ann Arbor, Michigan, 48109Michael Schall - Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, 48824Douglas A Gage - Department of Pharmaceutical Sciences, The University of Montana, Missoula, Montana, 59812Todd T Talley - Department of Chemistry, The University of Montana, Missoula, Montana, 59812Charles M Thompson - Department of Chemistry, The University of Montana, Missoula, Montana, 59812Rudy J Richardson - Toxicology Program, The University of Michigan, Ann Arbor, Michigan, 48109
- Resource Type
- Journal article
- Publication Details
- Toxicology and applied pharmacology, Vol.176(2), pp.73-80
- Publisher
- Elsevier Inc
- DOI
- 10.1006/taap.2001.9279
- PMID
- 11601883
- ISSN
- 0041-008X
- eISSN
- 1096-0333
- Language
- English
- Date published
- 10/15/2001
- Academic Unit
- Iowa Neuroscience Institute; Pharmaceutical Sciences and Experimental Therapeutics; Medicinal and Natural Products Chemistry
- Record Identifier
- 9984070779702771
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