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

A beta-xylosidase was induced and purified from the culture filtrate of Tri choderma koningii G-39, grown in a medium containing 1% oat spelts xylan an d 0.1% xylose, The presence of xylose unequivocally enhanced the induction of beta-xylosidase. The purified enzyme, which exhibited a significant alph a-arabinosidase activity, was obtained with high yield simply via ethanol p recipitation and a single anion-exchange chromatography and was characteriz ed as a monomeric glycoprotein with an estimated molecular mass of 104 kDa and a pl of 4.6. The K-m values towards P-nitrophenyl beta-D-xylopyranoside and p-nitrophenyl alpha-L-arabinopyranoside are 0.04 and 7.5 mM, respectiv ely. It is stable at pH 2.5-7.4, 37 degrees C. The pH and temperature optim a are in the range of 3.5-4.0 and 55-60 degrees C, respectively. Contrary t o most beta-xylosidases from other sources, Hg2+ (up to 25 mM) has no effec t on enzyme activity. Xylose was shown to inhibit the purified enzyme with a moderate Ki value of 5 mM, The enzyme exhibited transxylosylation activit y and was characterized as a 'retaining' enzyme, catalysing the hydrolysis of substrate with the retention of anomeric configuration.