Effect of pH on the Dehydrogenative Polymerization of Monolignols by Laccases from Trametes versicolor and Rhus vernicifera.

Abstract

Dehydrogenative polymerization of coniferyl alcohol (CA) and sinapyl alcohol (SA) was conducted using commercial laccases, fungal laccase from Trametes versicolor (LacT) and plant laccase from Rhus vernicifera (LacR), at pH 4–7 to investigate how the enzymatic polymerization of monolignols differs between these two laccase systems. The enzyme activity of LacT was the highest at pH 4, whereas that of LacR was the highest at pH 7. A dehydrogenation polymer (DHP) was obtained only from CA in both laccase systems, although the consumption rate of SA was higher than that of CA. 1H–13C HSQC NMR analysis showed that DHPs obtained using LacT and LacR contained lignin substructures, including β-O-4, β-O-4/α-O-4, β-β, and β-5 structures. At pH 4.5, the β-O-4 structure was preferentially formed over the β-O-4/α-O-4 structure, whereas at pH 6.5, the β-O-4/α-O-4 structure was preferred. The pH of the reaction solution was more vital to affect the chemical structure of DHP than the origin of laccases.