Steric and redox issues of phenolic and non-phenolic substrates are investigated for a better insight of the reactivity features of the phenoloxidase laccase. Whenever a substrate is endowed with a redox potential too high for direct monoelectronic oxidation by the enzyme, or else is too much encumbered to access the enzymatic pocket, redox mediators overcome the problem, behaving as an interface between enzyme and substrate. For example, the small-sized mediator ABTS, once oxidised by laccase, fruitfully interacts with bulky substrates, 2,4,6-tri(Bu')-phenol providing a significant case. Other mediators, for example HBT, resort to a radical oxidation mechanism precluded to laccase, and can react with non-phenolic substrates which are impossible for the enzyme. The advantages provided by the mediators are discussed, and suitable phenolic compounds, as precursors of phenoxyl radical intermediates, emerge as a new proficient class. They could be the true natural mediators of laccase in the oxidative delignification. In fact, phenoxyl radical fragments generated by laccase from lignin, or from phenolic monomer residuals from the building up of lignin polymer or else deriving from lignin by oxidation with other ligninolytic enzymes, could oxidise non-phenolic residues of lignin thereby causing the breakdown of its alkyl network. The novel mechanistic probe 3,5-di(Bu')-4-OH-benzyl alcohol enables the decoupling of the reactivity channels of a phenolic vs. a benzylic alcohol moiety in the enzymatic oxidation of bifunctional substrates having structural features comparable to portions of lignin. Experimental support is thereby attained for the central role of laccase in biodelignification, in spite of the seemingly lower oxidation power of this enzyme with respect to other and stronger oxidising enzymes excreted by ligninolytic fungi.

Mechanistic and steric issues in the oxidation of phenolic and non-phenolic compounds by laccase or laccase-mediator systems. The case of bifunctional substrates / Francesca, D'Acunzo; Galli, Carlo; Gentili, Patrizia; Federica, Sergi. - In: NEW JOURNAL OF CHEMISTRY. - ISSN 1144-0546. - STAMPA. - 30:4(2006), pp. 583-591. [10.1039/b516719a]

Mechanistic and steric issues in the oxidation of phenolic and non-phenolic compounds by laccase or laccase-mediator systems. The case of bifunctional substrates

GALLI, Carlo;GENTILI, Patrizia;
2006

Abstract

Steric and redox issues of phenolic and non-phenolic substrates are investigated for a better insight of the reactivity features of the phenoloxidase laccase. Whenever a substrate is endowed with a redox potential too high for direct monoelectronic oxidation by the enzyme, or else is too much encumbered to access the enzymatic pocket, redox mediators overcome the problem, behaving as an interface between enzyme and substrate. For example, the small-sized mediator ABTS, once oxidised by laccase, fruitfully interacts with bulky substrates, 2,4,6-tri(Bu')-phenol providing a significant case. Other mediators, for example HBT, resort to a radical oxidation mechanism precluded to laccase, and can react with non-phenolic substrates which are impossible for the enzyme. The advantages provided by the mediators are discussed, and suitable phenolic compounds, as precursors of phenoxyl radical intermediates, emerge as a new proficient class. They could be the true natural mediators of laccase in the oxidative delignification. In fact, phenoxyl radical fragments generated by laccase from lignin, or from phenolic monomer residuals from the building up of lignin polymer or else deriving from lignin by oxidation with other ligninolytic enzymes, could oxidise non-phenolic residues of lignin thereby causing the breakdown of its alkyl network. The novel mechanistic probe 3,5-di(Bu')-4-OH-benzyl alcohol enables the decoupling of the reactivity channels of a phenolic vs. a benzylic alcohol moiety in the enzymatic oxidation of bifunctional substrates having structural features comparable to portions of lignin. Experimental support is thereby attained for the central role of laccase in biodelignification, in spite of the seemingly lower oxidation power of this enzyme with respect to other and stronger oxidising enzymes excreted by ligninolytic fungi.
File allegati a questo prodotto
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/236917
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 96
  • ???jsp.display-item.citation.isi??? 91
social impact