Effect of lignin degradation product sinapyl alcohol on laccase catalysis during lignin degradation

Lignin is an excellent source of biomass; enzymatic hydrolysis of lignin is the key to its efficient use. The degradation activity of ligninase is affected by binding reactions with degradation products of lignin. In this paper, sinapyl alcohol (SA), a product of lignin degradation by laccase (LAC, a ligninase), was investigated as a mediator in enzymatic hydrolysis of lignin. This reaction was evaluated by molecular modelling, spectroscopic, dynamic light scattering, electrochemical experiments, gas chromatograph-mass spectrometer (GC–MS), nuclear magnetic resonance (NMR) and high-performance liquid chromatography (HPLC). These approaches allow elucidation of conformational changes in LAC caused by SA binding; confirm spontaneous binding between SA and LAC and electron transfer; determine the binding mode of SA with LAC; and enable determination of the mechanism of participation of the phenolic mediator SA in oxidation reactions after identification of 2,6-dimethoxy-1,4-benzoquinone (DMQ); besides, the effects of initial concentration of SA on the yields of DMQ; Our study shows how a small molecule mediator binds to LAC to form highly active intermediates, offering important insight into the processes involved in degradation of biomass.