Free-hydroxyl phenolic units can decrease or even abort the catalytic activity of lignin peroxidase HE during oxidation of veratryl alcohol and model lignin dimers, resulting in slow and inefficient lignin degradation. In this study we applied engineered 4-O-methyltransferase from Clarkia breweri to detoxify the inhibiting free-hydroxyl phenolic groups by converting them to methylated phenolic groups. The multistep, enzyme-catalyzed process that combines 4-O-methyltransferase and lignin peroxidase H8 suggested in this work can increase the efficiency of lignin-degradation. This study also suggests approaching the field of multi-enzyme in vitro systems to improve the understanding and development of plant biomass in biorefinery operations. (C) 2014 Elsevier Inc. All rights reserved.