Hydrolysis of diethyl diferulates by a tannase from Aspergillus oryzae
´ M.-T. Garcıa-Conesa a,*, P. Østergaard b, S. Kauppinen b, G. Williamson a a Phytochemicals Team, Division of Diet, Health & Consumer Sciences, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK. b ´ Screening Biotechnology, Enzyme Research Novo Nordisk A/S, Novo Alle, bldg. 1BM1.05 DK-2880 Bagsvaerd, Denmark.
Abstract Diferulic acid forms cross-links in naturally occurring plant cell wall polymers such as arabinoxylans and pectins. We have used model ethyl esterified substrates to find enzymes able to break these cross-links. A tannase from Aspergillus oryzae exhibited esterase activity on several synthetic ethyl esterified diferulates. The efficiency of this esterase activity on most diferulates is low compared to that of a cinnamoyl esterase, FAEA, from Aspergillus niger. Of the diferulate substrates assayed, tannase was most efficient at hydrolysing the first ester bond of the 5–5- type of dimer. Importantly and unlike the cinnamoyl esterase, tannase from A. oryzae is able to hydrolyse both ester bonds from the 8–5-benzofuran dimer, thus forming the corresponding free acid product. These results suggest that tannases may contribute to plant cell wall degradation by cleaving some of the cross-links existing between cell wall polymers. 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Aspergillus oryzae; cell wall polymers; Diethyl diferulates
1. Introduction Micro-organisms need to produce a combination of enzymes, primarily carbohydrases and ‘esterases’ (able to remove side chain substituents) that act synergistically, in order to increase digestibility of the plant cell wall. Crosslinking of the cell wall polymers by ferulic acid dehydrodimers: 8–5-, 8–O–4-, 5–5- and 8–8- diFAs (Ralph, Quideau, Grabbber & Hatfield, 1994) (Fig. 1), is a major obstacle which limits the
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