Lignin is a highly methylated, recalcitrant biopolymer available aplenty in nature, and is highly heteropolymer in nature, but yet it has been an under-utilized biopolymer. Modifying it chemically, biologically or enzymatically could render it a good candidate for phenol formaldehyde resin or into fine chemicals, fuels, and plastics applications. Lignin demethylation is facilitated by the enzymes called the O-demethylases, which are able to strip-off of the –OCH₃ group in lignin, that give rise to the more widely accessible phenolic hydroxyls groups. Biological demethylation of lignins can be accomplished by means of the microorganisms, such as the white-rot, soft-rot and brown-rot fungi, besides some species of bacteria. Although the enzymes responsible for the lignin demethylation process have not been identified and purified adequately, it is perhaps possible that the O-demethylases, which have the ability to remove the O-methyl groups at the C-3 and (or) C-4 positions of the benzyl ring of low molecular weight lignin-like model compounds (LMCs) and lignin makes them the suitable candidate. These LMCs resemble the aromatic moieties inherent in the molecular structure of lignins, such as the vanillate, syringate, and veratrate. Thus, these enzymes are known as vanillate-O-demethylases, syringate O-demethylases, veratrate O-demethylases and Tetrahydrofolate (THF)-dependent O-demethylase (LigM), respectively. Whereas, some ligninolytic enzymes are known to cause damage to the structure of lignins (e.g., laccases, manganese-dependent peroxidase and lignin peroxidases). The O-demethylase enzymes are believed to be capable of removing the O-methyl groups from the lignins without affecting the complex backbone structure of the lignins. The mechanism of action of O-demethylases on lignin degradation is still largely unexplored, and their ability to remove the O-methyl groups from lignins has not been elucidated sufficiently. In this review, the recent advances made on the molecular approaches in the lignin demethylation (O-demethylases and ligninolytic enzymes), degradation and the probable strategies to tone up the lignin quality have been discussed in detail. The demethylation process of lignins by means of enzymes is envisaged to open up new vistas for its application as a biopolymer in various bioprocess and biorefinery process.

木质素是自然界中大量可用的高度甲基化的顽固生物聚合物，自然界中是高度杂聚物，但是它一直未被充分利用。通过化学，生物或酶学修饰可以使其成为酚醛树脂或精细化学品，燃料和塑料应用的良好候选者。木质素的脱甲基作用被称为O-脱甲基酶的酶所促进，该酶能够去除–OCH ₃木质素中的基团，产生了更广泛可及的酚羟基基团。木质素的生物脱甲基可以通过除某些细菌种类之外的微生物来实现，例如白腐病，软腐病和棕腐病真菌。尽管尚未充分鉴定和纯化负责木质素脱甲基化过程的酶，但可能有能力去除O的O-脱甲基酶低分子量木质素样模型化合物（LMCs）和木质素的苄基环的C-3和（或）C-4位上的-甲基使它们成为合适的候选物。这些LMC类似于木质素分子结构中固有的芳族部分，例如香草酸酯，丁香酸酯和藜芦酸酯。因此，这些酶已知为vanillate- ö -demethylases，丁香ö -demethylases，veratrate ö四氢叶酸（THF） -依赖性-demethylases和ö -demethylase分别（LIGM）。然而，已知某些木质素分解酶会破坏木质素的结构（例如漆酶，锰依赖性过氧化物酶和木质素过氧化物酶）。该Ø据信β-脱甲基酶能够从木质素去除O-甲基而不影响木质素的复杂骨架结构。O-脱甲基酶对木质素降解的作用机理仍未被充分研究，并且它们从木质素中去除O-甲基的能力尚未得到充分阐明。在这篇综述中，木质素脱甲基化（O的分子方法的最新进展-脱甲基酶和木质素分解酶），降解以及提高木质素质量的可能策略已进行了详细讨论。木质素通过酶的脱甲基过程被设想开辟了新的前景，以将其用作生物聚合物在各种生物过程和生物精炼过程中的应用。