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

摘要

Acetyl esterase was produced by Streptomyces sp. PC22 at comparable levels of about 0.3 U ml?1 using either 1.0% (w/v) birchwood xylan or 1.5% (w/v) corn husks as a carbon source and cultivating at 45 °C, at 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 chromatography using a Macro-Prep DEAE, t-butyl hydrophobic interaction and hydroxyapatite, respectively. The approximate molecular weight of the purified enzyme was 155 kDa as analyzed by gel filtration, and it contained four identical 34 kDa subunits, as assessed by SDS-PAGE. It had K m and V max values for p-nitrophenyl acetate of 0.43 mM and 70.78 U mg?1 and 7.8 mM and 1,027 U mg?1 for α-naphthyl acetate, respectively. Its optimal pH and temperature were 6.5–7.0 and 50 °C, respectively. It was stable for 30 min at a broad range of pH values, from 5.0 to 9.0, and at temperatures up to 60 °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 β-xylosidase from Streptomyces sp. CH7. Enhancement was 1.4-fold, compared to the expected amount of 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.