Relative activity of endoxylanases towards water-extractable and water-unextractable arabinoxylan

Differences in endo-beta -1,4-xylanase functionality reult from the different ability of the enzymes to convert water-unextractable arabinoxylan (WU-AX) into solubilised AX (S-AX) and to degrade water-extractable arabinoxylan (WE-AX) and S-AX to lower molecular weight. These respective endoxylanse activities and their relative proportions were deternubed for two endoxylanses from Bacillus subtilis and Aspergillus aculeatus, according to a generally applicable procedure. Isolated wheat WE-AX and WU-AX containing wheat squeege starch prepared and incubated with different levels of endoxylanases. The supernatants were analysed for reducing xylose (RX) formed and WU-AX solublised. Molecular weights of the products formed were assessed. Relstive activities differed widely for the two endoxylanses. Based on the results and additional enzyme-substrate binding experiments, mechanisms possibly accounting for these differences are discussed. (C) 2001 Academic Press.