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Purification and characterization of two xylanases from alkalophilic and thermophilic Bacillus licheniformis 77-2
Authors:Valquiria B. Damiano  Richard Ward  Eleni Gomes  Heloiza Ferreira Alves-Prado  Roberto Da Silva
Affiliation:1. Biochemistry and Applied Microbiology Laboratory, UNESP-State University of S?o Paulo, Rua Cristóv?o Colombo n 2265, 15054-000, S?o José do Rio Preto, SP, Brazil
2. Biology Institute, UNESP-State University of S?o Paulo, Rio Claro, SP
3. Chemistry Institute, USP-University of S?o Paulo, Ribeir?o Preto, SP
Abstract:The alkalophilic bacteria Bacillus licheniformis 77-2 produces significant quantities of thermostable cellulase-free xylanases. The crude xylanase was purified to apparent homogeneity by gel filtration (G-75) and ionic exchange chromatography (carboxymethyl sephadex, Q sepharose, and Mono Q), resulting in the isolation of two xylanases. The molecular masses of the enzymes were estimated to be 17 kDa (X-I) and 40 kDa (X-II), as determined by SDS-PAGE. The K m and V max values were 1.8 mg/mL and 7.05 U/mg protein (X-I), and 1.05 mg/mL and 9.1 U/mg protein (X-II). The xylanases demonstrated optimum activity at pH 7.0 and 8.0–10.0 for xylanase X-I and X-II, respectively, and, retained more than 75% of hydrolytic activity up to pH 11.0. The purified enzymes were most active at 70 and 75°C for X-I and X-II, respectively, and, retained more than 90% of hydrolytic activity after 1 h of heating at 50°C and 60°C for X-I and X-II, respectively. The predominant products of xylan hydrolysates indicated that these enzymes were endoxylanases.
Keywords:Xylanase   Bacillus licheniformis   xylanase purification  alkalophilic bacteria  xylanase characterization
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