Activity of an esterase from Pseudomonas fluorescens subsp. cellulosa (XYLD) on an insoluble feruloylated hemicellulose substrate (de-starched wheat bran) was dependent on the source of added endo-xylanase. The esterase exhibited high selectivity for the nature, position of linkage and size of the feruloylated oligosaccharides generated by hydrolysis of the hemicellulose. Increased affinity of XYLD with increasing size of the oligosaccharide substrate suggests that optimal activity is observed on substrates with at least 4 sugars.
1D NMR (1H and 13C) and 2D NMR spectroscopy have been used to determine the structure of feruloylated oligosaccharides obtained by enzymic degradation or mild acid hydrolysis of sugar-beet pulp. Feruloylated oligosaccharides derived from pectic neutral side-chains containing arabinose or galactose residues were identified. In the feruloylated arabinose oligosaccharides, feruloyl groups were linked to O-2 of L-Ara f residues. The structure of the feruloylated arabinose disaccharide was identified as O-[2-O-(transferuloyl)-alpha-L-Ara f]-(1-->5)-L-Ara f and that of the feruloylated arabinose trisaccharide as O-alpha-L-Ara f-(1-->3)-O-[2-O-(trans-feruloyl)-alpha-L-Ara f]-(1-->5)-L- Ara f. The structure of the feruloylated galactose disaccharide was identified as O-[6-O-(trans-feruloyl) -beta-D-Gal p]-(1-->4)-D-Gal p. From our results, we suggest that the feruloyl groups present in sugar-beet pulp are linked to the arabinofuranosyl residues of the main core of alpha-(1-->5)-linked arabinan chains and to the galactopyranosyl residues of the main core of beta-(1-->4)-linked type I galactan chains.
        
Title: Degradation of feruloylated oligosaccharides from sugar-beet pulp and wheat bran by ferulic acid esterases from Aspergillus niger Ralet MC, Faulds CB, Williamson G, Thibault JF Ref: Carbohydr Res, 263:257, 1994 : PubMed
The activity of two forms of ferulic acid esterase (FAE) from Aspergillus niger on a synthetic feruloylated substrate (methyl ferulate) and on 11 different feruloylated oligosaccharides from sugar-beet pulp and wheat bran was determined. The enzymes exhibited different specificities for the various feruloylated substrates and were more active on certain substrates of cell-wall origin than on methyl ferulate. Both enzymes preferred the arabinose residue to which ferulic acid is attached in the furanose form. FAE-I had no clear preference for the type of linkage involved between the ferulic acid units and the oligosaccharide chain. In contrast, FAE-III had a clear requirement for ferulic acid to be attached to O-5 of the Ara f ring while no catalysis was observed when ferulic acid was attached to O-2. Both enzymes showed maximum activity on feruloylated trisaccharides. An increase in the length of the oligosaccharide chain did not preclude catalysis, but feruloylated oligosaccharides of a dp > 3 were hydrolysed at a reduced rate. Our results support the hypothesis that different kinds of ferulic acid esterases exist with different specificities for the oligosaccharide chain of the feruloylated substrates.