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-β-1,4-xylanase, α-l-arabinofuranosidase and β-xylosidase. The extracellular α-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 α-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 α-l-arabinofuranosidase exhibited maximal activity at pH 6.0–7.0 and an optimal temperature at 55 °C. The half-life of the α-l-arabinofuranosidase at 60 °C was approximately 2 h and it was very stable over a wide pH range for 24 h at 4 °C. The apparent Michaelis constant Km value of the α-l-arabinofuranosidase was 0.77 mM for p-nitropenyl-α-l-arabinofuranoside. The turnover number (Kcat) and catalytic efficiency (Kcat/Km) 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 α-l-arabinofuranosidase was specific for the α-linked arabinoside in the furanoside configuration and can also retain 52% of its activity in the presence of p-nitrophenyl-β-d-xylopyranoside as substrate. α-l-arabinofuranosidase acted synergistically with the immobilized endo-β-1,4-xylanase for the breakdown of alkali-extracted arabinoxylan and in the improvement of xylobiose and monosaccharide production.