Kinetic and thermodynamic characterization of a halotolerant -galactosidase produced by halotolerant Aspergillus tubingensis GR1

b-Galactosidase from halotolerant Aspergillus tubingensis GR1 was purified by two-step purification process comprising ammonium sulfate precipitation followed by size exclusion chromatography (SEC). The recovery of -galactosidase after SEC was found to be 1.40% with 58.55-fold increase in specific activity. The molecular weight of -galactosidase protein was found to be 93kDa by SDS-PAGE. Activation energy for O-nitrophenol -D-galactopyranoside (ONPG) hydrolysis was 32.88kJmol(-1), while temperature quotient (Q(10)) was found to be 1.375. The enzyme was found to be stable over wide pH range and thermally stable at 60-65 degrees C up to 60min of incubation while exhibited maximum activity at 65 degrees C with pH 3.0. V-max, K-m, and K-cat for ONPG were found to be 2000Uml(-1), 8.33mM (ONPG), and 101454s(-1), respectively. Activation energy for irreversible inactivation Ea(d) of -galactosidase was 100.017kJmol(-1). Thermodynamic parameters of irreversible inactivation of -galactosidase and ONPG hydrolysis were also determined. However, -galactosidase enzyme activity was activated significantly in the presence of 15% NaCl and hence shows activity up to 30% NaCl concentration.