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Biotechnology and Applied Biochemistry (2000) 31, (119–125) (Printed in Great Britain)

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

Yaw-Kuen Li¹, Hsin-Jan Yao and Yi-tzu Cho

Department of Applied Chemistry, National Chiao Tung University, Hsin-Chu,Taiwan, 30050, People's Republic of China

¹ To whom correspondence should be addressed.

A b-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 b-xylosidase. The purified enzyme, which exhibited a significant a-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 b-D-xylopyranoside and p-nitrophenyl a-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 b-xylosidases from other sources, Hg²⁺ (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.

Received 23 July 1999/4 Janaury 2000; accepted 13 January 2000

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