Ortho-Nitrophenyl-β-galactoside

Ortho-Nitrophenyl-β-galactoside (often abbreviated as ONPG) is a colorimetric and spectrophotometric substrate for detection of β-galactosidase activity. This compound is commonly used in molecular biology, specifically in the Lac operon model of prokaryotic gene regulation.

Structure and Properties[edit | edit source]

Ortho-Nitrophenyl-β-galactoside is a synthetic compound that consists of a galactose molecule linked to a nitrophenyl group. The galactose is in the beta configuration, meaning that the hydroxyl group attached to its anomeric carbon is oriented in the same direction as the C5 hydroxymethyl group.

Usage in Molecular Biology[edit | edit source]

In molecular biology, ONPG is used as a soluble substitute for lactose in the Lac operon system. In the presence of the enzyme β-galactosidase, ONPG is hydrolyzed to galactose and ortho-nitrophenol. The latter is a yellow compound that can be detected visually or with a spectrophotometer, allowing researchers to measure β-galactosidase activity and, by extension, the activity of the Lac operon.

File:ONPG hydrolysis.png

Hydrolysis of ONPG by β-galactosidase, producing galactose and ortho-nitrophenol.

Safety and Handling[edit | edit source]

Like many nitrophenol compounds, ONPG is moderately toxic and should be handled with care. It may cause skin and eye irritation, and ingestion or inhalation should be avoided. In case of exposure, affected areas should be washed thoroughly and medical attention should be sought if necessary.