Center for BioProcess Engineering, Dept. of Chemical and Biochemical Engineering, Building 229, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
Center for BioProcess Engineering, Dept. of Chemical and Biochemical Engineering, Building 229, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
Biotechnol Adv. 2015 Jan-Feb;33(1):13-24. doi: 10.1016/j.biotechadv.2014.12.008. Epub 2015 Jan 3.
Modification of lignin is recognized as an important aspect of the successful refining of lignocellulosic biomass, and enzyme-assisted processing and upcycling of lignin is receiving significant attention in the literature. Laccases (EC 1.10.3.2) are taking the centerstage of this attention, since these enzymes may help degrading lignin, using oxygen as the oxidant. Laccases can catalyze polymerization of lignin, but the question is whether and how laccases can directly catalyze modification of lignin via catalytic bond cleavage. Via a thorough review of the available literature and detailed illustrations of the putative laccase catalyzed reactions, including the possible reactions of the reactive radical intermediates taking place after the initial oxidation of the phenol-hydroxyl groups, we show that i) Laccase activity is able to catalyze bond cleavage in low molecular weight phenolic lignin model compounds; ii) For laccases to catalyze inter-unit bond cleavage in lignin substrates, the presence of a mediator system is required. Clearly, the higher the redox potential of the laccase enzyme, the broader the range of substrates, including o- and p-diphenols, aminophenols, methoxy-substituted phenols, benzenethiols, polyphenols, and polyamines, which may be oxidized. In addition, the currently available analytical methods that can be used to detect enzyme catalyzed changes in lignin are summarized, and an improved nomenclature for unequivocal interpretation of the action of laccases on lignin is proposed.
木质素的修饰被认为是木质纤维素生物质成功精炼的一个重要方面，并且酶辅助处理和木质素的升级利用在文献中受到了极大的关注。漆酶（EC 1.10.3.2）成为了关注的焦点，因为这些酶可以帮助降解木质素，使用氧气作为氧化剂。漆酶可以催化木质素的聚合，但问题是漆酶是否以及如何通过催化键断裂直接催化木质素的修饰。通过对现有文献的全面回顾和对假定的漆酶催化反应的详细说明，包括在酚羟基的初始氧化后可能发生的反应性自由基中间体的可能反应，我们表明：i）漆酶活性能够催化低分子量酚类木质素模型化合物中的键断裂；ii）对于漆酶催化木质素底物中单元间键的断裂，需要存在介体系统。显然，漆酶酶的氧化还原电位越高，能够被氧化的底物范围就越广，包括邻苯二酚、氨基酚、甲氧基取代的酚、苯硫酚、多酚和多胺。此外，还总结了目前可用于检测木质素酶催化变化的分析方法，并提出了一种改进的命名法，用于明确解释漆酶对木质素的作用。
