Purification and Properties of Endoxylanase Produced byBacillus pumilus

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Abstract
Extracellular endoxylanase (l,4-β-d-xylan xylanohydrolase [EC 3.2.1.8]) produced by Bacillus pumilus IPO, an isolate from soil in Thailand, was purified to homogeneity. The optimum pH and temperature of the purified xylanase for hydrolysis of larchwood xylan were 6.5 and 40°C. Its molecular weight was estimated to be 24,000 dalton by SDS-polyacrylamide gel electrophoresis and 20,000 dalton by equilibrium centrifugation. The number of amino acid residues per molecule was calculated to be 185, including one cysteine. The maximum degree of hydrolysis of larchwood xylan by the purified xylanase was 25%; xylobiose, xylotriose, xylotetraose and xylopentaose but not xylose were detected as end-products. trans-Xylosidase activity was indicated by the formation of xylobiose and xylotetraose from xylotriose and of xylopentaose and hexaose in addition to biose and triose from xylotetraose. Quantification of hydrolysis products indicated that the enzyme′s greatest affinity was for the 2nd to 6th β-xylosidic linkages from the terminal of larchwood xylan.

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