Purification and Properties of Beta‐galactosidase from <i>Streptococcus thermophilus</i>

Abstract

ABSTRACT A β‐galactosidase from Streptococcus thermophilus was purified to homogeneity by ammonium sulfate and acetone fractionation, gel filtration on Sephadex G‐200, and ion exchange chromatography on DEAE‐Sephadex A‐50. The purified enzyme preparation exhibited an optimum pH at 6.6–7.0 and an optimum temperature of 57°C. The enzyme was stable at pH 6.8–7.0. Km and V max for the enzyme, using ortho‐nitrophenyl β‐D‐galactopyranoside as the substrate, were 0.25 mM and 83 μmoles/mg protein/min, respectively. It was strongly inhibited by Hg ++ , Ag + , and Cu ++ as well as pchloro‐mercuri benzoate. The enzyme had a molecular weight of about 6 × 10 5 and was highly specific for β‐galactoside bonds.