Aspergillus fumigates ?-Galactosidase: Purification and Characterization

?-Galactosidase (?-D-galactoside galactohydrolase) is an exotype glycoside hydrolase that catalyzes the hydrolysis of ?-1,6-galactosidic linkages in galactose-containing oligosaccharides such as melibiose (galactose- ?-1,6-glucose), raffinose (galactose- ?-1,6-sucrose), and stachyose (galactose- ?-1,6-raffinose) and in galactomannan. An ?-galactosidase (a-D-galactosidegalactohydrolase was purified to homogeneity from the culture filtrate of Aspergillus fumigatus. ?-Galactosidase was induced by galactose, melibiose and raffinose, but galactose was the most efficient inducer. ?-galactosidase was purified by gel filtration and two ion exchange chromatography’s and showed Mw of 54.7 kDa. The purified enzyme showed maximal activity against p-nitrophenyl-?-D-galactopyranoside (pNPGal) at pH 4.5-5.5 and 55 °C, and retained about 80% of the original activity after incubation for 90 minutes at 50ºC. The KM for pNPGal was 0.3 mM. Melibiose was hydrolyzed by the enzyme but raffinose was very poor substrate.