Purification and characterization of alkali-tolerant xylanases from Aspergillus tamarii

A strain of Aspergillus tamarii isolated from soil produced two different cellulase-free xylanases when developed on corn cob powder as the only carbon source. The two enzymes, designated xylanase I and II, were purified to apparent homogeneity by ammonium sulfate precipitation followed by chromatography on DEAE-cellulose and Sephadex G-100. The molecular weigths estimated by SDS electrophoresis and Sephadex G-100 filtration were 12,500 and 28,000 Da, respectively to xylanase I and II. The enzymes I and II had a carbohydrate: content estimated as 39 and 12.7%, respectively. The apparent Km values, using birchwood xylan as substrate, were 5.8 and 8.4 mg/ml and Vmax. values were 6.94 x 10(2) and 1.7 x 10(3) mu mol.ml(-1).mg(-1), respectively to enzymes I and II. The hydrolysis patterns demonstrated that the xylanases were endoenzymes. Both enzymes yielded mainly xylobiose and higher xylooligosaccharides from xylan. The Aspergillus tamarii xylanases were stab re at large range of alkaline pH and they were able to hydrolyse xylan at pH 8.0.