Production and Characterization of β‐Galactosidase from <i>Streptococcus thermophilus</i>

Abstract

ABSTRACT Crude β‐galatosidase was produced by lysis of cells of Streptococcus thermophilus grown on deproteinized whey. The enzyme was partially purified by ammonium sulfate precipitation and ion‐exchange chromatography to yield a preparation free of protease activity. Highest activity was observed at pH 7.1, in the presence of potassium and manganese ions. Both monovalent and divalent cations were required for maximum activity but not for stability. The K m for o ‐nitrophenyl‐β‐galactopyranoside and lactose was 0.98 mM and 6.9 mM, respectively. Galactose was a competitive inhibitor with K i of 60 mM. Gel‐filtration indicated a molecular weight of 530,000. The enzyme seems well suited to hydrolysis of lactose in milk.