초록
<P>The high‐level expression of the xylanase GH11 gene from <I>Aspergillus niger</I> IA‐001 called <I>xynB</I> was successfully completed in <I>Pichia pastoris</I>. The <I>xynB</I> gene encoding a mature xylanase of 225 amino acid was subcloned into the pPICZαA vector and was transformed into <I>P. pastoris</I> X‐33 under the control of the alcohol oxidase I (AOX1) promoter. The <I>xynB</I> gene was ligated with a sequence encoding modified α‐factor signal peptide (pPICZαmA) and the recombinant xylanase activity, which was measured 1280 U ml<SUP>−1</SUP>, was 1.5‐fold higher than when it was inserted into pPICZαA and was 19.39‐fold greater than the native xylanase in the original strain. In a 10 L fermenter, the recombinant xylanase activity measured 10,035 U ml<SUP>−1</SUP> after 114 h. The SDS–PAGE analysis revealed that the purified xynB protein migrated as a single band with an apparent molecular weight of 24 kDa. The specific activity, using beechwood xylan as a substrate, was 1916 U mg<SUP>−1</SUP>. The xylanase activity was optimal at pH 5.0 and at 50 °C. In addition, the xynB was active over a pH range of 2.2 to 10.0. The apparent <I>K</I><SUB><I>m</I></SUB> and <I>V</I><SUB><I>max</I></SUB> values were 4.429 mg ml<SUP>−1</SUP> and 1429 U mg<SUP>−1</SUP>, respectively.</P>