Isolation and properties of extracellular beta-xylosidases from fungi Aspergillus japonicus and Trichoderma reesei.

Homogeneous beta-xylosidases with molecular mass values 120 and 80 kDa (as shown by SDS-PAGE), belonging to the third family of glycosyl hydrolases, were isolated by anion-exchange, hydrophobic, and gel-penetrating chromatography from enzyme preparations based on the fungi Aspergillus japonicus and Trichoderma reesei, respectively. The enzymes exhibit maximal activity in acidic media (pH 3.5-4.0), and temperature activity optimum was 70 degrees C for the beta-xylosidase of A. japonicus and 60 degrees C for the beta-xylosidase of T. reesei. Kinetic parameters of p-nitrophenyl beta-xylopyranoside and xylooligosaccharide hydrolysis by the purified enzymes were determined, which showed that beta-xylosidase of A. japonicus was more specific towards low molecular weight substrates, while beta-xylosidase of T. reesei preferred high molecular weight substrates. The competitive type of inhibition by reaction product (xylose) was found for both enzymes. The interaction of the enzymes of different specificity upon hydrolysis of glucurono- and arabinoxylans was found. The beta-xylosidases exhibit synergism with endoxylanase upon hydrolysis of glucuronoxylan as well as with alpha-L-arabinofuranosidase and endoxylanase upon hydrolysis of arabinoxylan. Addition of beta-xylosidases increased efficiency of hydrolysis of plant raw materials with high hemicellulose content (maize cobs) by the enzymic preparation Celloviridine G20x depleted of its own beta-xylosidase.