X-gal (also abbreviated BCIG for 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside) is an organic compound consisting of galactose linked to a substituted indole. The compound was synthesized by Jerome Horwitz and collaborators in 1964. [1]

X-Gal (5-bromo-4-chloro-3-indolyl-β-D-galactoside) is a histochemical substrate for β-galactosidase. This substrate yields a blue precipitate upon hydrolysis, making it suitable for use in immunoblotting or immunocytochemical assays.

How Does Blue White Screening Work? For screening the clones containing recombinant DNA, a chromogenic substrate known as X-gal is added to the agar plate. If β-galactosidase is produced, X-gal is hydrolyzed to form 5-bromo-4-chloro-indoxyl, which spontaneously dimerizes to produce an insoluble blue pigment called 5,5’-dibromo-4,4’-dichloro-indigo.

X-gal is a colorless soluble compound that consists of galactose linked to a substituted indole. β-Gal has high specificity toward the galactose moiety than the remaining. X-gal is reduced to an insoluble blue color product while releasing the indole part free by the action of β-Gal.

X-Gal is a widely used chromogenic substrate for β-galactosidase. It yields a dark blue precipitate at the site of enzymatic activity. X-Gal is useful for numerous histochemical and molecular biology applications, including detection of lacZ activity in cells and tissues.

X-Gal is a chromogenic substrate for β-galactosidase that produces a rich blue color that can easily be detected visually over background. X-Gal is the substrate of choice for blue-white selection of recombinant bacterial colonies with the lac + genotype.

X-Gal is a cell permeable, chromogenic substrate for β-galactosidase. It consits of galactose linked to a substituted indole. β-galactosidase hydrolyzes X-gal to release an insoluble, bright blue precipitate.

X-Gal (5-Bromo-4-Chloro-3-Indolyl-beta-D-Galactoside) is a chromogenic substrate for β-galactosidase that yields a blue precipitate upon hydrolysis.

Galactopyranoside chromogenic substrates, such as X-Gal and its alternatives like Bluo-Gal and Magenta-Gal, are histochemical substrate for β-galactosidase which cleaves the galactopyranoside to yield an insoluble blue (or red in the case of Magenta-Gal) precipitate.

X-Gal is widely used in molecular biology as chromogenic substrate for β -galactosidase. The enzyme hydrolyses this colourless compound into a colourless intermediate, which then dimerizes and gets oxidized into a blue final product (Figure 1).