Degradation of Lignin Glycosides by Lignin Oxidizing Enzymes

为了阐明糖苷的形成对酶体系降解木质素的影响，用辣根过氧化物酶、漆酶和木质素过氧化物酶处理DHP和DHP-葡萄糖苷。在氧化过程中，DHP的反应混合物的颜色从淡黄色变成深棕色，最后形成沉淀。另一方面，DHP-Glc的反应混合物的颜色仅从淡黄色变为浅棕色，并且根本没有形成沉淀。通过凝胶过滤色谱分析对照和酶处理样品的分子量分布。分子量分布曲线表明，漆酶或过氧化物酶对DHP的氧化反应是聚合反应，而不是降解反应，而DHP-Glc则是酶催化解聚反应。在这里采用的处理条件下，DHP-Glc更广泛地降解成低分子量组分的过氧化物酶处理（辣根过氧化物酶和木质素过氧化物酶），而不是漆酶处理（商业漆酶和漆酶III）。在本研究中，我们已经观察到，葡萄糖苷DHP木质素可以降解过氧化物酶和漆酶处理。虽然木质素糖苷在体外可能的降解机制尚未阐明，目前的结果表明，必须存在一个系统，其中糖苷的形成防止聚合和加速有效的降解反应。

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.