Merck, 10105031001, β-Galactosidase

General description
β-Galactosidase or β-D-Galactoside galactohydrolase is basically a tetramer made up of identical four polypeptide chains, each constituting 1023 amino acids. It is very specific for D-galactose and requires K⁺ or Na⁺ and Mg²⁺ to be fully active. β-Galactosidase enzyme with an oxygen glycosidic bond catalyzes reactions with β-d-galactopyranosides.
At 37 °C with 2-nitrophenyl-β-D-galactoside as the substrate, approximately 30 U/mg at 25 °C with lactose as the substrate; standardized with BSA.
Application
β-galactosidase has been used in enzyme-linked immunosorbent assay (ELISA). Use β-Galactosidase to produce a calibration curve in enzymatic assays.
Biochem/physiol Actions
Cleaves terminal galactose residues that are β1,4-linked to a monosaccharide, oligosaccharide, or glycopeptide.
Physical form
Suspension, in 3.2 M ammonium sulfate solution, pH approximately 6, crystalline
Preparation Note
The ammonium sulfate preparation is stable at 2 to 8 °C until the expiration date printed on the label. Use directly for most applications, e.g., quantitation of lactose.

In the absence of ammonium sulfate, solutions of β-galactosidase should be stabilized with Mg²⁺ (89 mM) and a thiol reagent (1mM β-mercaptoethanol, 1 mM dithiothreitol) [Beutler, 1984]. The thiol slows the formation of enzyme dimers resulting from intramolecular disulfide bridges.

Activator: K (50 mM) is required for activation (lactose hydrolysis).
Na (50 mM) is also an activator, particularly for hydrolysis of 2-nitrophenyl-β-D-galactopyranoside.
Analysis Note
Contaminants: <0.01% GIDH, GPT, LDH, MDH, and oxaloacetate decarboxylase, each
Other Notes
For life science research only. Not for use in diagnostic procedures.