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

Abstract

Abstract 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 K m value of the α- l -arabinofuranosidase was 0.77 mM for p -nitropeny l -α- 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 Hg 2+ and Cu 2+ inhibited enzyme activity, whereas it was strongly activated by Mn 2+ . 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.