2-Nitrophenyl β-D-galactopyranoside

Chromogenic substrate for β-galactosidase

ONPG (2-Nitrophenyl β-D-galactopyranoside) is a colorimetric substrate for β-galactosidase.

2-Nitrophenyl β-D-galactopyranoside is an enzyme substrate used to detect lacZ activity and hence the presence of β-galactosidase.

β-galactosidase, breaks down lactose into galactose and glucose. β-Galactosidase is not lactose specific and can act on simple galactosides. 2-Nitrophenyl β-D-galactopyranoside hydrolysis results in the release of galactose and a yellow chromogenic compound. The test substrate does not depend on an induced or constitutive permease enzyme to enter the cell, therefore reactions are rapid and occur within a 24-hour period.

A stock solution can be prepared in molecular biology grade water at a concentration of 3 mg/ml. Alternatively, a stock solution of approximately 20.5 mg/ml is prepared in 100 mM sodium phosphate buffer (pH 7.3). Gentle warming may be required to completely dissolve the product.