5-Bromo-3-indolyl β-D-galactopyranoside

5-Bromo-3-indolyl β-D-galactopyranoside (Bluo-Gal) is a chromogenic substrate for β-galactosidase. 5-Bromo-3-indolyl β-D-galactopyranoside is hydrolyzed by the enzyme to generate a 5-bromoindole intermediate, which is further oxidized to form an insoluble blue precipitate. 5-Bromo-3-indolyl β-D-galactopyranoside can specifically recognize bacterial β-galactosidases (such as the product of the Escherichia coli lacZ gene) and reacts at pH 7.4, making it suitable for light and electron microscopic observations. 5-Bromo-3-indolyl β-D-galactopyranoside can be used in histochemical detection of reporter gene expression in transgenic organisms, such as the localization analysis of β-galactosidase activity in mouse embryos or muscle tissues.