Degradation of Lignin Glycosides by Lignin Oxidizing Enzymes

为了阐明糖苷的形成对酶系统降解木质素的影响，用辣根过氧化物酶、漆酶和木质素过氧化物酶对DHP和DHP-葡萄糖苷进行处理。在氧化过程中，DHP的反应混合物由淡黄色变为深棕色，最终形成沉淀。而DHP-GLC的反应混合物则从淡黄色变为淡棕色，根本没有形成沉淀。用凝胶过滤层析分析了对照和酶处理样品的相对分子质量分布。所有的分子量分布图都清楚地表明，DHP被含有漆酶或过氧化物酶的酶系统氧化导致聚合，而不是降解。另一方面，当DHP-GLC被这些酶处理时，观察到酶催化的解聚。在所采用的处理条件下，过氧化物酶处理(辣根过氧化物酶和木质素过氧化物酶)比漆酶处理(商品漆酶和漆酶III)能更广泛地将DHP-GLC降解为低分子量组分。在本研究中，我们观察到糖苷DHP木质素可以被过氧化物酶和漆酶处理降解。虽然木质素糖苷的体外降解机理尚未阐明，但目前的结果表明，一定存在一种糖苷的形成阻止聚合并加速有效的降解反应的体系。

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.