Enzymatic valorisation of lignin-based monophenolic multi-substrate solutions via tyrosine phenol lyase

Monophenolic multi-substrate solutions were studied in the synthetic reaction catalysed by the tyrosine phenol lyase variant M379V (TPL-M379V). Composition of the substrate solution was mimicked based on lignin-derived pyrolysis bio-oil with selected monophenols. The enzymatic synthesis of L -tyrosine derived amino acids was successful with a substrate solution of five main monophenols: guaiacol, phenol, o-cresol, m-cresol and syringol. A total monophenol conversion of 74.17% was reached. Three other monophenols were studied as inhibitors: catechol, vanillin and 4-methylguaiacol. Vanillin was found to be the most significant inhibitor (total monophenol conversion 42.97%), whereas the combined effect of all three inhibitors did not significantly accumulate the inhibitory effects (37.89% total monophenol conversion). The presence of vanillin was also found to suppress excess substrate degradation in the reaction medium and prevent the assumed side reaction of catechol autoxidation into catechol melanin. The least inhibition of the three studied compounds was caused by 4-methylguaiacol (71.38% total monophenol conversion). However, at higher concentrations the inhibition became more prominent. These results highlight the potential of the enzymatic valorisation of lignin-derived monophenolics and serve as a key-step towards the TPL-M379V-catalysed synthesis of high-value aromatic amino acid products from lignin. • High total monophenol conversion with lignin-based monophenolic substrate solution. • Substrate solution composition based on lignin-derived pyrolytic bio-oil. • Vanillin was found to be the most significant inhibitor, followed by catechol. • Combination of three inhibitors did not increase overall inhibition.