Aging pathways for organophosphate-inhibited human butyrylcholinesterase, including novel pathways for isomalathion, resolved by mass spectrometry.
Some organophosphorus compounds are toxic because they inhibit acetylcholinesterase (AChE) by phosphylation of the active site serine, forming a stable conjugate: Ser-O-P(O)-(Y)-(XR) (where X can be O, N, or S and Y can be methyl, OR, or SR). The inhibited enzyme can undergo an aging process, during which the X-R moiety is dealkylated by breaking either the P-X or the X-R bond depending on the specific compound, leading to a nonreactivatable enzyme. Aging mechanisms have been studied primarily using AChE. However, some recent studies have indicated that organophosphate-inhibited butyrylcholinesterase (BChE) may age through an alternative pathway. Our work utilized matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry to study the aging mechanism of human BChE inhibited by dichlorvos, echothiophate, diisopropylfluorophosphate (DFP), isomalathion, soman, sarin, cyclohexyl sarin, VX, and VR. Inhibited BChE was aged in the presence of H2O18 to allow incorporation of (18)O, if cleavage was at the P-X bond. Tryptic-peptide organophosphate conjugates were identified through peptide mass mapping. Our results showed no aging of VX- and VR-treated BChE at 25 degrees C, pH 7.0. However, BChE inhibited by dichlorvos, echothiophate, DFP, soman, sarin, and cyclohexyl sarin aged exclusively through O-C bond cleavage, i.e., the classical X-R scission pathway. In contrast, isomalathion aged through both X-R and P-X pathways; the main aged product resulted from P-S bond cleavage and a minor product resulted from O-C and/or S-C bond cleavage.
Li
He
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Eppley Institute and Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805, USA.
Schopfer
Lawrence M
LM
Nachon
Florian
F
Froment
Marie-Thérèse
MT
Masson
Patrick
P
Lockridge
Oksana
O
D002091:Butyrylcholinesterase / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D002619:Chemical Warfare Agents / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D002800:Cholinesterase Inhibitors / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D017666:Deuterium Oxide; D004006:Dichlorvos / Q000737:chemistry; D004456:Echothiophate Iodide / Q000737:chemistry; D004795:Enzyme Stability; D006801:Humans; D007306:Insecticides / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D007531:Isoflurophate / Q000737:chemistry; D008294:Malathion / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D015394:Molecular Structure; D010449:Peptide Mapping / Q000379:methods; D012524:Sarin / Q000031:analogs & derivatives / Q000737:chemistry; D012694:Serine / Q000737:chemistry; D012999:Soman / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors; D014357:Trypsin
D002619:Chemical Warfare Agents; D002800:Cholinesterase Inhibitors; D007306:Insecticides; D007531:Isoflurophate; D012694:Serine; D004006:Dichlorvos; D012999:Soman; C018326:isomalathion; D012524:Sarin; D004456:Echothiophate Iodide; D002091:Butyrylcholinesterase; D014357:Trypsin; D017666:Deuterium Oxide; D008294:Malathion