Effective induction, purification and characterization of Trichoderma koningii G‐39 β‐xylosidase with high transferase activity

A β‐xylosidase was induced and purified from the culture filtrate of Trichoderma koningii G‐39, grown in a medium containing 1% oat spelts xylan and 0.1% xylose. The presence of xylose unequivocally enhanced the induction of β‐xylosidase. The purified enzyme, which exhibited a significant α‐arabinosidase activity, was obtained with high yield simply via ethanol precipitation and a single anion‐exchange chromatography and was characterized as a monomeric glycoprotein with an estimated molecular mass of 104 kDa and a pI of 4.6. The K m values towards p ‐nitrophenyl β‐D‐xylopyranoside and p ‐nitrophenyl α‐L‐arabinopyranoside are 0.04 and 7.5 mM, respectively. It is stable at pH 2.5–7.4, 37 °C. The pH and temperature optima are in the range of 3.5–4.0 and 55–60 °C, respectively. Contrary to most β‐xylosidases from other sources, Hg 2+ (up to 25 mM) has no effect on enzyme activity. Xylose was shown to inhibit the purified enzyme with a moderate K i value of 5 mM. The enzyme exhibited transxylosylation activity and was characterized as a ‘retaining’ enzyme, catalysing the hydrolysis of substrate with the retention of anomeric configuration.