Purification and characterization of novel bifunctional xylanase, XynIII, isolated from Aspergillus niger A-25
2006; Springer Science+Business Media; Volume: 16; Issue: 7 Linguagem: Inglês
ISSN
1738-8872
AutoresHong Ge Chen, Yan Xin, Xin Yu Liu, Ming Dao Wang, Hui Huang, Xin Cheng Jia, J.A. Wang,
Tópico(s)Studies on Chitinases and Chitosanases
ResumoThree types of xylanases (EC 3.2.1.8) were detected in the strain Aspergillus niger A-25, one of which, designated as XynIII, also displayed β-(1,3-l,4)-glucanase (EC 3.2.1.73) activity, as determined by a zymogram analysis. XynIII was purified by ultrafiltration and ion-exchange chromatography methods. Its apparent molecular weight was about 27.9 kDa, as estimated by SDS-PAGE. The purified XynIII could hydrolyze birchwood xylan, oat spelt xylan, lichenin, and barley β-glucan, but not CMC, avicel cellulose, or soluble starch under the assay conditions in this study. The xylanase and β-(1,3-1,4)-glucanase activities of XynIII both had a similar optimal pH and pH stability, as well as a similar optimal temperature and temperature stability. Moreover, the effects of metal ions on the two enzymatic activities were also similar. The overall hydrolytic rates of XynIII in different mixtures of xylan and lichenin coincided with those calculated using the Michaelis-Menten model when assuming the two substrates were competing for the same active site in the enzyme. Accordingly, the results indicated that XynIII is a novel bifunctional enzyme and its xylanase and β-(1,3-l,4)-glucanase activities are catalyzed by the same active center.
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