Description_x000D_ Application_x000D_ β-Galactosidase from Escherichia coli has been used as an internal standard in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). It has been used in the protein ladder mix for optimization of microfluidic western blotting assay._x000D_ Biochem/physiol Actions_x000D_ β-galactosidase cleaves lactose into its monosaccharide components, glucose and galactose. It also catalyses the transglycosylation of glucose into allolactose, the inducer of β-galactosidase, in a feedback loop._x000D_ Physical properties_x000D_ Tetramer molecular weight 465 kDa (subunits 116.3 kDa each)_x000D_ Unit Definition_x000D_ One unit will hydrolyze 1.0 μmole of o-nitrophenyl β-D-galactoside to o-nitrophenol and D-galactose per min at pH 7.3 at 37 °C.