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

摘要

An arabinogalactan 3-beta-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 deg C and the optimal stability was observed at pH 4.0 and below50 deg C. All enzymatic activity was inhibited completely by the addition Hg~(2+) ions Lineweaver-Burk plots showed a Michaelis constant (K_m) of 0 89 and 4 74 mg/ml and a maximum reaction velocity (V_(max)) 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 arable, and curdlan, all of which contains beta-(1-->3) and alpha-(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.