Production, purification, and characterization of acetyl esterase from Streptomyces sp. PC22 and its action in cooperation with xylanolytic enzymes on xylan degradation.

摘要

Production, purification and characterization of a bacterial xylan degrading enzyme is reported. Acetyl esterase was produced by Streptomyces sp. PC22 at a level of about 0.3 U/ml using either 1.0% (w/v) birchwood xylan or 1.5% (w/v) corn husks as a C source with fermentation at 45 degrees C, and pH 9 for 3 or 2 days, respectively. The enzyme was purified from culture filtrate to about 54-fold purity by ammonium sulfate precipitation, followed by consecutive Macro-Prep DEAE, t-butyl hydrophobic interaction and hydroxyapatite chromatography steps, respectively. The mol. wt. of the purified enzyme was 155 kDa as analysed by gel filtration, and it contained 4 identical 34 kDa subunits, as assessed by SDS-PAGE. It had Km and Vmax values for p-nitrophenyl acetate of 0.43mM and 70.78 U/mg and 7.8mM and 1027 U/mg for alpha-naphthyl acetate, respectively. Its optimal pH and temp. were 6.5-7.0 and 50 degrees C, respectively. The enzyme was stable for 30 min at a broad range of pH values, from 5.0 to 9.0, and at temp. up to 60 degrees C. The purified enzyme had no other xylanolytic activities. It showed cooperative action on birchwood xylan degradation, when used in combination with xylanase from the same strain and beta-xylosidase from Streptomyces sp. CH7. An increase of 4-fold was obtained compared with the expected amount of the individual enzymes alone. This indicates that the enzyme has potential industrial applications, especially for utilizing renewable hemicelluloses containing acetyl xylan for the production of biofuels or other fermentation products.