Isolation and some properties of β-galactosidase from the thermophilic bacterium Thermus thermophilus

The highest β-galactosidase activity in Thermus thermophilus cells was achieved after 40 h of cultivation at 70°C in a medium containing 0.8% peptone, 0.4% yeast extract and 0.2% NaCl. After the addition to the medium of 2% of lactose or galactose, enzyme synthesis in the cells increased by about 33% and 61% of its constitutive value. The thermostable β-galactosidase isolation and partial purification involved extraction in 0.01 m phosphate buffer at pH 7.2, ammonium sulphate precipitation, dialysis and gel filtration on Sephadex G-200 or lyophilization. The highest recovery yield of activity during the isolation process was about 72% of its total value in the extract. The gel filtration step resulted in an increase of β-galactosidase specific activity of two-fold more than the ammonium sulphate precipitate. The crude enzyme obtained exhibited highest activity at pH 6.6 and 87°C. Decimal reduction times of activity at 75, 80, 85, 90 and 95°C were 174, 50, 22, 5.5 and 0.9 h, respectively..