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Transition State Analysis of the Reaction Catalyzed by the Phosphotriesterase from Sphingobium sp. TCM1.
Bigley, Andrew N; Xiang, Dao Feng; Narindoshvili, Tamari; Burgert, Charlie W; Hengge, Alvan C; Raushel, Frank M.
Afiliación
  • Bigley AN; Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States.
  • Xiang DF; Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States.
  • Narindoshvili T; Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States.
  • Burgert CW; Department of Chemistry and Biochemistry , Utah State University , Logan , Utah 84322 , United States.
  • Hengge AC; Department of Chemistry and Biochemistry , Utah State University , Logan , Utah 84322 , United States.
  • Raushel FM; Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States.
Biochemistry ; 58(9): 1246-1259, 2019 03 05.
Article en En | MEDLINE | ID: mdl-30730705
Organophosphorus flame retardants are stable toxic compounds used in nearly all durable plastic products and are considered major emerging pollutants. The phosphotriesterase from Sphingobium sp. TCM1 ( Sb-PTE) is one of the few enzymes known to be able to hydrolyze organophosphorus flame retardants such as triphenyl phosphate and tris(2-chloroethyl) phosphate. The effectiveness of Sb-PTE for the hydrolysis of these organophosphates appears to arise from its ability to hydrolyze unactivated alkyl and phenolic esters from the central phosphorus core. How Sb-PTE is able to catalyze the hydrolysis of the unactivated substituents is not known. To interrogate the catalytic hydrolysis mechanism of Sb-PTE, the pH dependence of the reaction and the effects of changing the solvent viscosity were determined. These experiments were complemented by measurement of the primary and secondary 18-oxygen isotope effects on substrate hydrolysis and a determination of the effects of changing the p Ka of the leaving group on the magnitude of the rate constants for hydrolysis. Collectively, the results indicated that a single group must be ionized for nucleophilic attack and that a separate general acid is not involved in protonation of the leaving group. The Brønsted analysis and the heavy atom kinetic isotope effects are consistent with an early associative transition state with subsequent proton transfers not being rate limiting. A novel binding mode of the substrate to the binuclear metal center and a catalytic mechanism are proposed to explain the unusual ability of Sb-PTE to hydrolyze unactivated esters from a wide range of organophosphate substrates.
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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Organofosfatos / Sphingomonadaceae / Hidrolasas de Triéster Fosfórico Idioma: En Revista: Biochemistry Año: 2019 Tipo del documento: Article País de afiliación: Estados Unidos Pais de publicación: Estados Unidos
Texto completo
Añadir a Mi BVS
Imprimir
XML
PubMed Links
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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Asunto principal: Organofosfatos / Sphingomonadaceae / Hidrolasas de Triéster Fosfórico Idioma: En Revista: Biochemistry Año: 2019 Tipo del documento: Article País de afiliación: Estados Unidos Pais de publicación: Estados Unidos