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Enzymatic Hydrolysis of Black Liquor Xylan by a Novel Xylose-Tolerant, Thermostable β-Xylosidase from a Tropical Strain of Aureobasidium pullulans CBS 135684

Bankeeree, Wichanee, Akada, Rinji, Lotrakul, Pongtharin, Punnapayak, Hunsa, Prasongsuk, Sehanat
Applied biochemistry and biotechnology 2018 v.184 no.3 pp. 919-934
Aureobasidium pullulans, enzymatic hydrolysis, half life, hydrolysis, pH, temperature, thermal stability, waste liquors, xylan, xylan 1,4-beta-xylosidase, xylose
From three cell-associated β-xylosidases produced by Aureobasidium pullulans CBS 135684, the principal enzyme was enriched to apparent homogeneity and found to be active at high temperatures (60–70 °C) over a pH range of 5–9 with a specific activity of 163.3 units (U) mg⁻¹. The enzyme was thermostable, retaining over 80% of its initial activity after a 12-h incubation at 60 °C, with half-lives of 38, 22, and 10 h at 60, 65, and 70 °C, respectively. Moreover, it was tolerant to xylose inhibition with a K ᵢ value of 18 mM. The K ₘ and V ₘₐₓ values against p-nitrophenyl-β-d-xylopyranoside were 5.57 ± 0.27 mM and 137.0 ± 4.8 μmol min⁻¹ mg⁻¹ protein, respectively. When combining this β-xylosidase with xylanase from the same A. pullulans strain, the rate of black liquor xylan hydrolysis was significantly improved by up to 1.6-fold. The maximum xylose yield (0.812 ± 0.015 g g⁻¹ dry weight) was obtained from a reaction mixture containing 10% (w/v) black liquor xylan, 6 U g⁻¹ β-xylosidase and 16 U g⁻¹ xylanase after incubation for 4 h at 70 °C and pH 6.0.