Purification and Properties of β-Galactosidases from Bacillus circulans

Abstract

β-Galactosidases (EC 3.2.1.23) from Bacillus circulans were purified and separated into two different enzyme forms, using Sephadex G-150, ion-exchange, polybuffer chromatography, and preparative polyacrylamide gel electrophoresis. The molecular weights estimated for these two enzymes were 2.4×10⁵ (β-galactosidase-1) and 1.6×10⁵(β-galactosidase-2). They showed similar isoelectric points of about 4.5 and the same optimum pH of 6.0, whereas they were considerably different in Km values, substrate specificity, and particularly oligosaccharide-producing activity. β-Galactosidase-2 produced many galacto-oligosaccharides, including di-, tri-, tetra-, and pentasaccharides, during hydrolysis of 4.56% lactose. When 60% of the lactose was converted, the total amount of oligosaccharide production reached a maximum at which about 41% of the products formed were oligosaccharides. β-Galactosidase-1 produced only 6% at its maximum.