Depolymerization of Lignin and Mediators for Laccase
Abstract
Laccase is a multi-copper oxidase that converts electrons within protein molecules from the type I (blue Cu-S) copper site that receives electrons to the type II (normal mononuclear) and type III (magnetically-interacted Cu-O-Cu bridged dinuclear) copper sites that reduce oxygen (a function expected to be applied in biofuel cells). Near the monocuclear type I copper site, it accepts four (per a water molecule) electrons from external (organic or inorganic) substrates reduced and catalyzes various oxidation reactions. For this reason, it is used industrially not only as a catalyst for organic synthesis reactions, but also for bleaching organic pigments and decomposing lignin, a component of wood. However, the supply of electrons to the type I copper site is not always smooth (and is one of the bottlenecks in biofuel cells). For this purpose, mediator molecules are used to relay electrons. This chapter focuses on laccase mediators in lignin degradation and introduces related things such as lignin, laccase, mediator, laccase-mediator for lignin deporymerization, examples studies on mediators, and perspective.