Purification and biochemical characterization of two xylanases produced by Aspergillus caespitosus and their potential for kraft pulp bleaching

• Published in: Process biochemistry (1991) Vol. 40; no. 5; pp. 1823 - 1828
• Main Authors: Sandrim, V.C., Rizzatti, A.C.S., Terenzi, H.F., Jorge, J.A., Milagres, A.M.F., Polizeli, M.L.T.M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2005
• Subjects: Aspergillus caespitosus; Pulp bleaching; Xylanases; Aspergillus caespitosus; Xylanases; Pulp bleaching
• ISSN: 1359-5113; 1873-3298
• DOI: 10.1016/j.procbio.2004.06.061

Two extracellular xylanases produced by the thermotolerant fungus Aspergillus caespitosus grown in sugar cane bagasse were purified and characterized. Estimated molecular masses were 26.3 and 27 kDa (xyl I); 7.7 and 17.7 kDa (xyl II) for gel filtration and SDS-PAGE, respectively. Optimal temperature for both xylanases was 50–55 °C. Optimal pH was 6.5–7.0 for xyl I, and 5.5–6.5 for xyl II. The thermostability ( T half) at 55 °C was 27.3 min (xyl I) and >90 min (xyl II). Xylanase activity was inhibited by several ions. β-mercaptoethanol activated 59 and 102% xyl I and xyl II activities, respectively. These enzymes preferentially hydrolyzed birchwood xylan, and the K m and V max values were 2.5 mg/ml and 1679 U/mg protein (xyl I), and 3.9 mg/ml and 113 U/mg protein (xyl II). The action of both xylanases mainly that of xyl II, on kraft pulp reduced kappa number and increased pulp viscosity.