Direct Observation and Elucidation of the Structures of Aged and Nonaged Phosphorylated Cholinesterases by 31P NMR Spectroscopy
Abstract
31P NMR spectroscopy of butyrylcholinesterase (BChE), acetylcholinesterase (AChE), and chymotrypsin (Cht) inhibited by pinacolyl methylphosphonofluoridate (soman), methylphosphonodifluoridate (MPDF), and diisopropyl phosphorofluoridate (DFP) allowed direct observation of the OP- linked moiety of aged (nonreactivatable)and nonaged organophosphorus(OP)-ChE conjugates. The 31PNMR chemical shifts of OP-ChE conjugates clearly demonstrated insertion of a P-0 bond into the active site of aged OP-ChE adducts. The OP moiety of nonaged OP-ChEs was shown to be uncharged. The OP-bound pinacolyl moiety of soman-inhibited and aged AChE was detached completely, whereas only partial dealkylation of the pinacolyl group was observed for soman-inhibited BChEs. This suggests that the latter enzyme reacted with the less active stereoisomer(s) of soman. In the case of soman-inhibited Cht, no dealkylation could be experimentally detected for any of the four stereoisomers of OP-Cht adducts. Results are consistent with the contention that the phenomenon of enzyme-catalyzed dealkylation of OP adducts of serine hydrolases strongly depends on the orientation of both the catalytic His and the carboxyl side chain of either Glu or Asp positioned next to the catalytic Ser. The denatured protein of aged OP-ChE or OP-Cht is a convenient leaving group in nucleophilic displacements of tetrahedral OP compounds despite the presence of a P-0- bond. This indicates that the unusual resistance to reactivation of the aged enzyme cannot be ascribed to simple electrostatic repulsion of an approaching nucleophile.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 27, 1993
- Accession Number
- ADA275433
Entities
People
- B. P. Doctor
- D. Barak
- D. Waysbort
- N. Ariel
- Y. Segall
Organizations
- Walter Reed Army Institute of Research