Abstract
Enzymatic oxidation of 5-hydroxymethylfurfural (HMF) and its oxidized derivatives was studied using three fungal enzymes: wild-type aryl alcohol oxidase (AAO) from three fungal species, wild-type peroxygenase from Agrocybe aegerita (AaeUPO), and recombinant galactose oxidase (GAO). The effect of pH on different reaction steps was evaluated and apparent kinetic data (Michaelis-Menten constants, turnover numbers, specific constants) were calculated for different enzyme-substrate ratios and enzyme combinations. Finally, the target product, 2,5-furandicarboxylic acid (FDCA), was prepared in a multi-enzyme cascade reaction combining three fungal oxidoreductases at micro-scale. Furthermore, an oxidase-like reaction is proposed for heme-containing peroxidases, such as UPO, horseradish peroxidase, or catalase, causing the conversion of 5-formyl-2-furancarboxylic acid into FDCA in the absence of exogenous hydrogen peroxide.
Highlights
Plastics such as polyethylene terephthalates (PET) have become an integral part of human life, and the world’s annual consumption of such plastics has grown to about 40 million tons in 2014 and is forecasted to increase to over 70 million tons in 2020 [1,2]
Recombinant galactose oxidase (GAO) and catalase (Cat) expressed in Aspergillus oryzae were provided by Novozymes AS (Bagsværd, Denmark)
The final AaeUPO preparation had a specific activity of 82 U mg−1 measured with veratryl alcohol as substrate according to Ullrich et al [17]
Summary
Plastics such as polyethylene terephthalates (PET) have become an integral part of human life, and the world’s annual consumption of such plastics has grown to about 40 million tons in 2014 and is forecasted to increase to over 70 million tons in 2020 [1,2]. An increasing usage of fossil raw materials will inevitably end in the exhaustion of the world’s capacity. The fructose conversion product 5-hydroxymethylfurfural (HMF), a five-membered aromatic heterocycle, has come into the focus of polymer chemists as an alternative building block for the synthesis of PET-analogous polyesters deriving from renewable sources, such as starch [4,5]. In addition to bacterial whole-cell conversions [6,7], in the past years, some enzymatic reactions, including enzyme cascades, have been reported to produce FDCA from HMF by using flavin-dependent oxidoreductases, such as fungal aryl alcohol oxidase (AAO, EC 1.1.3.7) and heme-thiolate peroxidases (unspecific peroxygenase/UPO exclusively produced by fungi, EC 1.11.2.1; fungal chloroperoxidase/CPO, EC 1.11.1.10), or combinations of them [8,9,10,11]. In a recent patent, fungal galactose oxidase (GAO; EC 1.1.3.9), a rather unspecific copper-containing enzyme that oxidizes diverse sugars and alcohols [12], was reported to oxidize HMF in cooperation with
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