Catalytic properties of Talaromyces thermophilus α-L-arabinofuranosidase and its synergistic action with immobilized endo-β-1,4-xylanase

When grown on wheat bran, Talaromyces thermophilus produces a wide spectrum of hemicellulases, mainly endo-beta-1,4-xylanase, alpha-L-arabinofuranosidase and beta-xylosidase. The extracellular a-L-arabinofuranosidase was purified to homogeneity by sequential operation of ammonium sulfate precipitation, Q-sepharose column chromatography, gel filtration on Sephacryl S-200 and MonoQ column. The pure a-L-arabinofuranosidase had a specific activity of 49 U/mg of protein and was purified 26.7-fold. The molecular mass of the enzyme was estimated to be 35 kDa, determined by SDS-PAGE and by gel filtration. The alpha-L-arabinofuranosidase exhibited maximal activity at pH 6.0-7.0 and an optimal temperature at 55 degrees C. The half-life of the a-L-arabinofuranosidase at 60 degrees C was approximately 2 h and it was very stable over a wide pH range for 24h at 4 degrees C. The apparent Michaelis constant K-m value of the a-L-arabinofuranosidase was 0.77 mM for p-nitropenyL-alpha-L-arabinofuranoside. The turnover number (K-cat) and catalytic efficiency (K-cat/K-m) were found to be 14.3 s(-1) and 1.8 104 M-1 s(-1), respectively. Metal ions such as Hg2+ and Cu2+ inhibited enzyme activity, whereas it was strongly activated by Mn2+. The alpha-L-arabinofuranosidase was specific for the alpha-linked arabinoside in the furanoside configuration and can also retain 52% of its activity in the presence of p-nitropheny1-beta-D-xylopyranoside as substrate. alpha-L-arabinofuranosidase acted synergistically with the immobilized endo-beta-1,4-xylanase for the breakdown of alkali-extracted arabinoxylan and in the improvement of xylobiose and monosaccharide production. (c) 2010 Elsevier B.V. All rights reserved.