Isolation and Characterization of an β- (1→3) -D-Galactanase from the Strain of Aspergillus fumigatus No.232

An arabinogalactan 3-β-D-galactanohydrolase (EC 3. 2. 1. 90) from a culture broth of Aspergillus fumigatus No. 232 was isolated using ion-exchange chromatography on SP-Sephadex G-50 and gel filtration on Sephadex G-100. The galactanase apparent specific activity increased 19.7-fold after purification. This enzyme migrated as a single band in SDS-PAGE and had a molecular mass of 86, 000. The optimal activity was measured at pH 4.6 and 45°C and the optimal stability was observed at pH 4.0 and below 50°C. All enzymatic activity was inhibited completely by the addition Hg2+ ions. Lineweaver-Burk plots showed a Michaelis constant (Km) of 0.89 and 4.74 mg/m/ and a maximum reaction velocity (Vmax) of 3.16 and 6.54 unit/mg/min for hydrolysis of arabinogalactan from coffee bean and arabinogalactan from larch wood, respectively. This enzyme hydrolysed coffee bean arabinogalactan, larch wood arabinogalactan, gum arabic, and curdlan, all of which contains β- (1→3) and α- (1→3) -linkages in its structure, The hydrolysis products were arabinose, galactose, and galactobiose. It is likely that the substrate selectivity of the enzyme purified from Aspergillus fumigatus No. 232 was less specific to that of other galactanase.