title: Mechanism and stereochemical course at phosphorus of the reaction catalyzed by a bacterial phosphotriesterase.
abstract: The reaction mechanism for the phosphotriesterase from Pseudomonas diminuta has been examined. When paraoxon (diethyl 4-nitrophenyl phosphate) is hydrolyzed by this enzyme in oxygen-18-labeled water, the oxygen-18 label is found exclusively in the diethyl phosphate product. The absolute configurations for the (+) and (-) enantiomers of O-ethyl phenylphosphonothioic acid have been determined by X-ray diffraction structural determination of the individual crystalline 1-phenylethylamine salts. The (+) enantiomer of the free acid corresponds to the RP configuration. The RP enantiomer of O-ethyl phenylphosphonothioic acid has been converted to the SP enantiomer of EPN [O-ethyl O-(4-nitrophenyl) phenylphosphonothioate]. (SP)-EPN is hydrolyzed by the phosphotriesterase to the SP enantiomer of O-ethyl phenylphosphonothioic acid. The enzymatic reaction therefore proceeds with inversion of configuration. These results have been interpreted as an indication of a single in-line displacement by an activated water molecule directly at the phosphorus center of the phosphotriester substrate. (RP)-EPN is not hydrolyzed by the enzyme at an appreciable rate.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station 77843.
authors.forename: V E
authors.initials: VE
authors.lastname: Lewis
authors.forename: W J
authors.initials: WJ
authors.lastname: Donarski
authors.forename: J R
authors.initials: JR
authors.lastname: Wild
authors.forename: F M
authors.initials: FM
authors.lastname: Raushel
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D009946:Organothiophosphorus Compounds / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011549:Pseudomonas / Q000201:enzymology*; D013237:Stereoisomerism
chemical_list: D009946:Organothiophosphorus Compounds; D010744:Phosphoric Monoester Hydrolases