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

β-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 β-galactosidase after SEC was found to be 1.40% with 58.55-fold increase in specific activity. The molecular weight of β-galactosidase protein was found to be 93 kDa by SDS-PAGE. Activation energy for O-nitrophenol β-D-galactopyranoside (ONPG) hydrolysis was 32.88 kJ mol(-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°C up to 60 min of incubation while exhibited maximum activity at 65°C with pH 3.0. V(max), K(m), and K(cat) for ONPG were found to be 2000 U ml(-1), 8.33 mM (ONPG), and 101454 s(-1), respectively. Activation energy for irreversible inactivation Ea(d) of β-galactosidase was 100.017 kJ mol(-1). Thermodynamic parameters of irreversible inactivation of β-galactosidase and ONPG hydrolysis were also determined. However, β-galactosidase enzyme activity was activated significantly in the presence of 15% NaCl and hence shows activity up to 30% NaCl concentration.