X-Gal Powder | 5-Bromo-4-Chloro-3-indolyl β-D-galactopyranoside

5-bromo-4-chloro-3-indolyl β-D-galactopyranoside powder, also known as X-Gal, is a chromogenic substrate used in biology and chemistry. This substrate is an indicator of β-galactosidase activity.
X-Gal is a colorless substance at first. When this substrate is hydrolyzed by the enzyme β-galactosidase, the substance 5-bromo-4-chloro-3-hydroxyindole is formed. This compound is seen as a blue precipitate. The formation of the blue color is the colorimetric indicator for the activity of the enzyme β-galactosidase, which would allow the identification of positive bacterial colonies or samples.
Practical applications include its use to identify coliforms and Escherichia coli in culture media, which is a critical step in analyses of water and food samples.

Moreover, the formation of blue precipitate by X-Gal find utility in different immunological assays like Enzyme-Linked Immunosorbent Assays (ELISA).

In immunological assay, such as ELISA, the formation of the blue precipitate by X-Gal finds utility.
While used with IPTG as an inducer, X-Gal would induce the expression of the enzyme β-galactosidase in lac+ genotype bacteria. IPTG inhibits the lac repressor, which also allowed an increased expression of the enzyme.