Exhaustive laccase-catalysed oxidation of a lignin model compound (vanillyl glycol) produces methanol and polymeric quinoid products

Abstract

Laccase-catalysed oxidation of the lignin-related phenol vanillyl glycol results in the initial formation of dimers and subsequent polymerization. The polymerization is accompanied by a liberation of methanol corresponding to 15-20% demethylation. Visible spectra together with reduction experiments suggest the simultaneous formation of o-quinones. The participation of quinone formation in the polymerization process and the possible role of such intermediates in lignin biodegradation is discussed.

The early oxidative biodegradation steps of residual kraft lignin models with laccase

“…The diphenylmethane model 8, which showed the highest reactivity, also showed the highest amount of high molecular weight metabolites, probably arising from radical coupling reactions. 4,14,15 The strongly enhanced reactivity of 5-5 H , diphenylmethane and a-5 models in the presence of bubbled oxygen (which caused their near complete degradation), constitutes experimental evidence supporting our contention that the other experiments were performed under limited oxygen supply. This experimental design e ectively allowed the isolation and characterization of the early metabolites occurring during the laccase and laccase-mediator oxidative processes.…”

“…Such reactivity patterns have already been observed for laccase oxidations of lignins and lignin model compounds. 2,15,19 This behaviour is analogous to the overall reactivity found between hydroxy radicals and lignin model compounds. This analogy is reasonable since the main intermediates involved in such reactions are believed to be phenoxy radicals.…”

“…In the presence of higher enzyme activity another metabolite with a high molecular weight was detected, and tentatively assigned as being a compound possibly emerging via a radical coupling pathway. 4,14,15 When the fully methylated model 6 was incubated under the same experimental conditions, no reaction occurred, with the exception that traces of the dialdehyde 7 were detected in the presence of ABTS when high enzyme levels were used (Scheme 1). When the reaction was performed in the presence of bubbled oxygen, the extent of degradation was found to be 61.7% for model compound 1 in the presence of laccase alone, while the nonphenolic compound 6 was essentially unreacted even in the presence of ABTS or HBT.…”

Demethylation and delignification of kraft pulp by Trametes versicolor laccase in the presence of 2,2?-azinobis-(3-ethylbenzthiazoline-6-sulphonate)

“…Laccase is known to oxidize phenols and phenolic sub-structures of lignin by one-electron abstraction, giving radicals that can subsequently polymerize or depolymerize (Higuchi 1989;Kawai et al 1988;Ishihara 1980;Morohoshi et al 1987). The enzyme also demethylates phenolic lignin substructures (Ishihara and Miyazaki 1974;Lundquist and Kristersson 1985). We showed recently (Bourbonnais and Paice 1990) that the substrate range of laccase could be extended to non-phenolic lignin substructures by the presence of "primary" substrates, i.e., substrates that easily generate a stable radical.…”

Differential extracellular enzyme production in colonies of Coriolus versicolor, Phlebia radiata and Phlebia rufa: effect of gaseous regime

“…However, their association with different cultural morphologies may be discussed in view of previously postulated function or consequence. Laccase has been implicated in numerous processes, including morphogenesis (Devi et al, 1989;Wood et al, 1990), detoxification of phenolics (Moss, 1984), modification of protolignin and lignin (Morohoshi et al, 1989;Katayama et al, 1989), and control of lignin and cellulose degradation (Westermark & Eriksson, 1974;Lundquist & Kristersson, 1985;Morpeth & Jones, 1986). However, such patterns of enzyme production may simply reflect a physiological need for changes in carbon flow associated with new physiological activities (Paterson, 1988).…”