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

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. H-1-C-13 HSQC NMR analysis showed that DHPs obtained using LacT and LacR contained lignin substructures, including beta-O-4, beta-O-4/alpha-O-4, beta-beta, and beta-5 structures. At pH 4.5, the beta-O-4 structure was preferentially formed over the beta-O-4/alpha-O-4 structure, whereas at pH 6.5, the beta-O-4/alpha-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.

Automated summary

This study investigated the differences in enzymatic polymerization of monolignols in two laccase systems. The highest enzyme activity of LacT was observed at pH 4, while that of LacR was highest at pH 7. Only CA was able to produce a dehydrogenation polymer (DHP) in both laccase systems, although SA was consumed at a higher rate. H-1-C-13 HSQC NMR analysis revealed the presence of lignin substructures in the DHPs obtained using LacT and LacR. The pH of the reaction solution was found to have a greater impact on the chemical structure of DHP than the source of laccases.