Study on the characterization of a potential thermostable β-galactosidase from thermus thermophilus HB27

A β-galactosidase gene bgal from Thermus thermophilus was cloned and expressed in Escherichia coli. The optimum temperature for this β-galactosidase activity was 70 °C, at which it maintained stable. The optimal pH for enzyme activity is 6.5. The K
_m
value for ONPG was 3.5 mM, while in the presence of cysteine it decreased to 1.4 mM. Cysteine, β-mercaptoethanol, Fe
²⁺
or Mn
²⁺
promoted the enzymatic activity.