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Abstract
BackgroundIn the biorefinery utilizing lignocellulosic biomasses, lignin decomposition to value-added phenolic derivatives is a key issue, and recently biocatalytic delignification is emerging owing to its superior selectivity, low energy consumption, and unparalleled sustainability. However, besides heme-containing peroxidases and laccases, information about lignolytic biocatalysts is still limited till date.ResultsHerein, we report a promiscuous activity of tyrosinase which is closely associated with delignification requiring high redox potentials (>1.4 V vs. normal hydrogen electrode [NHE]). The promiscuous activity of tyrosinase not only oxidizes veratryl alcohol, a commonly used nonphenolic substrate for assaying ligninolytic activity, to veratraldehyde but also cleaves the 4-O-5 and Cα–Cβ bonds in 4-phenoxyphenol and guaiacyl glycerol-β-guaiacyl ether (GGE) that are dimeric lignin model compounds. Cyclic voltammograms additionally verified that the promiscuous activity oxidizes lignin-related high redox potential substrates.ConclusionThese results might be applicable for extending the versatility of tyrosinase toward biocatalytic delignification as well as suggesting a new perspective for sustainable lignin utilization. Furthermore, the results provide insight for exploring the previously unknown promiscuous activities of biocatalysts much more diverse than ever thought before, thereby innovatively expanding the applicable area of biocatalysis.
Highlights
In the biorefinery utilizing lignocellulosic biomasses, lignin decomposition to value-added phenolic derivatives is a key issue, and recently biocatalytic delignification is emerging owing to its superior selectivity, low energy consumption, and unparalleled sustainability
In order to broaden the enzymatic diversity of pretreating lignocellulosic biomasses and to increase the information about ligninolytic biocatalysts, we focused on tyrosinase (E.C. 1.14.18.1) which shows two catalytic activities for various phenolic compounds using O 2 as the electron acceptor: o-hydroxylation of monophenol to diphenol by a cresolase activity and oxidation of diphenol to quinone by a catecholase activity [15]
Tyrosinase catalyzed the conversion of veratryl alcohol to veratraldehyde, and the latter was identified by GC–MS with a retention time of 10.95 min and a mass spectrum of authentic veratraldehyde (Fig. 1; Additional file 1: Table S1)
Summary
In the biorefinery utilizing lignocellulosic biomasses, lignin decomposition to value-added phenolic derivatives is a key issue, and recently biocatalytic delignification is emerging owing to its superior selectivity, low energy consumption, and unparalleled sustainability. Besides heme-containing peroxidases and laccases, information about lignolytic biocatalysts is still limited till date. Heme-containing peroxidases such as lignin peroxidase (LiP, E.C. 1.11.1.14), manganese peroxidase (MnP, E.C. 1.11.1.13), versatile peroxidase (VP, E.C. 1.11.1.16), and dye-decolorizing peroxidase (DyP, E.C. 1.11.1.19) are known to be involved in delignification by catalyzing two-electron oxidation requiring a high redox potential of over +1.4 V (vs normal hydrogen electrode [NHE]) with hydrogen peroxide as an electron acceptor [11, 12]. Besides heme-containing peroxidases and laccase, information on other ligninolytic biocatalysts is very limited to date
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