title: Concerted electron/proton transfer mechanism in the oxidation of phenols by laccase.
abstract: This study aimed to assess structural requirements in the enzyme/substrate interactions that are responsible for tuning the enzymatic reactivity. To better assess the role of the aspartic residue in the substrate-binding pocket of basidiomycete-type laccases, we compared the catalytic efficiency of wild-type enzymes to that of a mutant in which carboxylic acid residue Asp206 was changed to alanine. Oxidation efficiency towards phenolic substrates by laccases of Trametes villosa, Trametes versicolor and a T. versicolor D206A mutant was studied at two pH values. By the Hammett approach and Marcus analysis, we obtained unambiguous evidence that the oxidation takes place by a concerted electron/proton transfer (EPT) mechanism, and that at pH 5 (optimum pH for enzyme activity) the phenolic proton is transferred to Asp206 during the concerted electron/proton transfer process.
authors.affiliation: Dipartimento di Chimica, Università "La Sapienza", and IMC-CNR Sezione Meccanismi di Reazione, P.le A. Moro 5, 00185 Roma (Italy).
authors.forename: Carlo
authors.initials: C
authors.lastname: Galli
authors.forename: Catherine
authors.initials: C
authors.lastname: Madzak
authors.forename: Raffaella
authors.initials: R
authors.lastname: Vadalà
authors.forename: Claude
authors.initials: C
authors.lastname: Jolivalt
authors.forename: Patrizia
authors.initials: P
authors.lastname: Gentili
mesh_terms: D004583:Electrons; D006863:Hydrogen-Ion Concentration; D042845:Laccase / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D010636:Phenols / Q000378:metabolism*; D017354:Point Mutation; D011522:Protons; D055454:Trametes / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D010636:Phenols; D011522:Protons; D042845:Laccase
keywords: concerted electron/proton transfer; laccase; mutagenesis; phenols