Mechanism and stereochemical course at phosphorus of the reaction catalyzed by a bacterial phosphotriesterase
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 R/sub P/ configuration. The R/sub P/ enantiomer of O-ethyl phenylphosphonothioic acid has been converted to the S/sub P/ enantiomer of EPN (O-ethyl O-(4-nitrophenyl) phenylphosphonothioate). (S/sub P/)-EPN is hydrolyzed by the phosphotriesterase to the S/sub P/ 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. (R/sub P/)-EPN is not hydrolyzed by the enzyme at an appreciable rate.
- Research Organization:
- Texas A and M Univ., College Station (USA)
- OSTI ID:
- 5380558
- Journal Information:
- Biochemistry; (United States), Vol. 27:5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ESTERASES
X-RAY DIFFRACTION
ORGANIC PHOSPHORUS COMPOUNDS
BIODEGRADATION
CHEMICAL REACTIONS
NUCLEAR MAGNETIC RESONANCE
OXYGEN 18
PESTICIDES
PHOSPHORUS 31
PSEUDOMONAS
PURIFICATION
STEREOCHEMISTRY
WATER
BACTERIA
COHERENT SCATTERING
DECOMPOSITION
DIFFRACTION
ENZYMES
EVEN-EVEN NUCLEI
HYDROGEN COMPOUNDS
HYDROLASES
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MICROORGANISMS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PHOSPHORUS ISOTOPES
RESONANCE
SCATTERING
STABLE ISOTOPES
550602* - Medicine- External Radiation in Diagnostics- (1980-)
550201 - Biochemistry- Tracer Techniques