PURIFICATION AND CHARACTERIZATION OF 2 XYLANASES AND AN ARABINOFURANOSIDASE FROM ASPERGILLUS-SOJAE

Two isoenzymes of xylanase (endo-1,4-beta-xylanase, EC 3.2.1.8) and an arabinofuranosidase (alpha-L-arabinofuranosidase, EC 3.2.1.55) were purified as electrophoretically homogeneous proteins from a solid-state culture of Aspergillus sojae. The molecular weights of the xylanases (X-I and X-II-B) and arabinofuranosidase (X-II-A) were estimated to be 32,700, 35,500 and 34,300, respectively, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Gel filtration chromatography gave molecular weight values similar to those obtained by SDS-PAGE for each of the purified enzymes. The isoelectric points of X-I and X-II-B were 3.50 and 3.75, and that of X-II-A was 3.90. The maximum velocities of arabinoxylan degradation by the xylanases were attained at 60 degrees C (X-I) and 50 degrees C (X-II-B), when the PPI was maintained at 5.5. The xylanases were stable from pH 5.0 to 8.0, and up to 50 degrees C (X-I) and 35 degrees C (X-II-B). The optimum pH and temperature of X-LT-A were 5.0 and 50 degrees C, respectively, and it was stable from pH 5.0 to 9.0 and up to 50 degrees C. The activity of these three enzymes was significantly inhibited by Mn2+ and EDTA, and stimulation by metal ions was not observed. Amino acid composition and sequence of the amino-terminus indicated that the xylanases of A. sojae were distinct from other known Aspergillus xylanases.