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An extracellular thermostable xylanase from a newly isolated thermophilic Actinomadura sp. strain Cpt20 was purified and characterized. Based on matrix-assisted laser desorption-ionization time-of-flight mass spectrometry analysis, the purified enzyme is a monomer with a molecular mass of 20,110.13 Da. The 19 residue N-terminal sequence of the enzyme showed 84% homology with those of actinomycete endoxylanases. The optimum pH and temperature values for xylanase activity were pH 10 and 80 °C, respectively. This xylanase was stable within a pH range of 5-10 and up to a temperature of 90 °C. It showed high thermostability at 60 °C for 5 days and half-life times at 90 °C and 100 °C were 2 and 1 h, respectively. The xylanase was specific for xylans, showing higher specific activity on soluble oat-spelt xylan followed by beechwood xylan. This enzyme obeyed the Michaelis-Menten kinetics, with the K (m) and k (cat) values being 1.55 mg soluble oat-spelt xylan/ml and 388 min(-1), respectively. While the xylanase from Actinomadura sp. Cpt20 was activated by Mn(2+), Ca(2+), and Cu(2+), it was, strongly inhibited by Hg(2+), Zn(2+), and Ba(2+). These properties make this enzyme a potential candidate for future use in biotechnological applications particularly in the pulp and paper industry.

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