Mode of action of family 10 and 11 endoxylanases on water-unextractable arabinoxylan

Microbial endo-beta-1,4-xylanases(EXs,EC3.2.1.8) belonging to glycanase families 10 and 11 differ in their action on water-unextractable arabinoxylan (WU-AX). WU-AX was incubated with different levels of a Thermoascus aurantiacus family 10 and a Sporotrichum thermophile family 11 endoxylanases. At 10 g l(-1) arabinoxylan, enzyme concentrations (K-E values) needed to obtain half-maximal hydrolysis rates (V-max values) were 4.4 nM for the xylanase from T aurantiacus and 7.1 nM for the xylanase from S. thermophile. Determination of V-max/K-E revealed that the family 10 enzyme hydrolysed two times more efficiently WU-AX than the family 11 enzyme. Molecular weights of the products formed were assessed and separation of feruloyl-oligosaccharides was achieved by anion-exchange and size-exclusion chromatography (SEC). The main difference between the feruloylated products by xylanases of family 10 and 11 concerned the length of the products containing feruloyl-arabinosyl substitution. The xylanase from T aurantiacus liberated from WU-AX a feruloyl arabinoxylodisaccharide (FAX(2)) as the shortest feruloylated fragment in contrast with the enzyme from S. thermophile, which liberated a feruloyl arabinoxylotrisaccharide (FAX(3)). These results indicated that different factors govern WU-AX breakdown by the two endoxylanases. (C) 2003 Elsevier B.V. All rights reserved.