α-l-Arabinofuranosidase from Streptomyces sp. PC22: Purification, characterization and its synergistic action with xylanolytic enzymes in the degradation of xylan and agricultural residues

α-l-Arabinofuranosidase was purified from culture filtrates of the thermoalkaliphilic Streptomyces sp. PC22 to about 108-fold purity by (NH4)2SO4 precipitation followed by column chromatography. Its approximate molecular weight was 404 kDa, with a subunit mass of 79 kDa. The evaluated Km and Vmax values with p-nitrophenyl-α-l-arabinofuranoside as substrate were 0.23 mM and 124 U • mg−1, respectively. The purified enzyme was optimally active at 65 °C and pH 6.0 and showed a mild but significant synergistic effect in combination with other xylanolytic enzymes, including xylanase, β-xylosidase and acetyl esterase, on the degradation of oat-spelt xylan, corn cob and corn husk substrates with a 1.25, 1.32 and 1.21-fold increase in the amount of reducing sugar released, respectively, compared to the expected (additive) amounts for the individual enzymes acting alone. Sequential reactions using two xylan-backbone degrading enzymes (xylanase/β-xylosidase) and two debranching enzymes (α-l-arabinofuranosidase/acetyl esterase) were also determined. The highest degree of synergy was obtained in sequential reactions with the debranching enzyme digestion preceding the xylan-backbone degrading enzymes.