Degradation of Lignin Glycosides by Lignin Oxidizing Enzymes

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In order to clarify the effect of the formation of glycoside on the degradation of lignin by enzyme systems, DHP and DHP-glucoside were treated with horseradish peroxidase, laccase and lignin peroxidase. During the oxidation, the reaction mixture of DHP changed color from yellowish to dark brown and finally formed precipitates. On the other hand, the reaction mixture of DHP-Glc just changed color from yellowish to pale brown and formed no precipitate at all. The molecular weight distribution of the control and enzyme treated samples was analyzed by gel filtration chromatography. All molecular weight distribution patterns obtained here showed clearly that oxidation of DHP by enzyme systems containing laccase or peroxidase resulted in polymerization and not degradation of DHP.On the other hand, when DHP-Glc was treated with the enzymes, enzyme-catalyzed depolymerization was observed. Under treatment conditions employed here, DHP-Glc was degraded more extensively into low molecular weight fractions by peroxidase treatment (horseradish peroxidase and lignin peroxidase) rather than laccase treatment (commercial laccase and laccase III). In the present study, we have observed that glucosidic DHP lignin can be degraded by peroxidase and laccase treatments. Although the mechanism for the possible degradation of lignin glycosides in vitro is not elucidated, the present results suggested that there must exist a system where the formation of glycoside prevents polymerization and accelerates efficient degradation reactions.