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

Abstract

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.

Purification and characterization of an exo-polygalacturonase secreted by Rhizopus oryzae MTCC 1987 and its role in retting of Crotalaria juncea fibre

“…3. The pH optimum of PG secreted by R. oryzae was found to be 5.0, similar to PG produced by Aspergillus ustus and Aspergillus japonicus (Rao et al 1996;Semenova et al 2003). The purified PG when exposed to various buffers at 20…”

“…The K m values of 2.5 mg/mL and 1.63 mg/mL for PG produced by Aspergillus niger and Streptomyces lydicus have been reported (Parenicova et al 1998;Jacob et al 2008) though a wide range of K m values (0.059-4.7 mg/mL) for PGs are also reported in the literature (Jayani et al 2005). The catalytic rate constant k cat of purified PG was found to be 2.23 × 10 3 s −1 which is significantly higher than those reported in the literature with 90 s −1 and 29 s −1 for PG-1 and PG-2 from Aspergillus japonicus which are endo-PGs (Semenova et al 2003). The authors could not find k cat values reported for exo-PGs for comparison.…”

Efficient Plant Biomass Degradation by Thermophilic Fungus Myceliophthora heterothallica

“…Since activity has been measured in the culture filtrate and xylotriose was absent during the saccharification, the conversion of xylobiose to xylose was likely prevented by-product inhibition of the ␤-xylosidases. This strong competitive type of inhibition by xylose has already been described for other fungal ␤-xylosidases (38)(39)(40). The introduction of a heterologous ␤-xylosidase with a lower inhibitor affinity can improve the release of fermentable xylose residues (41).…”

Pectinolytic complex production by Aspergillus niger URM 4645 using yellow passion fruit peels in solid state fermentation

“…However, Yadav et al (2008Yadav et al ( , 2009 reported the stability of PL from A. flavus and A. terricola at pH 4.0-10.0 and 4.0-9.0, respectively. PE from A. japonicus was stable at pH 3.5 to 5.5 (Semenova et al, 2003) and that from Aureobasidium pullulans was stable at pH 4.0 to 6.5 (Manachini et al, 1988).…”

“…was stable at temperatures up to 50°C (Fontana et al, 2005). PL and PE produced by A. japonicus showed stability between 40 and 50°C (Semenova et al, 2003). The most important factor among all the physical variables affecting the production of enzymes and metabolites is probably incubation temperature because enzymatic activities are sensitive to temperature (Krishna, 2005).…”