ONPG (2-Nitrophenyl β-D-galactopyranoside) is a colorimetric substrate for 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.
- Synonym: o-Nitrophenyl β-D-galactopyranoside, ONPG
- CAS Number: 369-07-3
- Empirical Formula (Hill Notation): C12H15NO8
- Molecular Weight: 301.25
- Beilstein Registry Number: 92207
- EC Number: 206-716-1
- MDL Number: MFCD00063255
- PubChem Substance ID: 24897461
- Grade: for molecular biology
- InChI Key: KUWPCJHYPSUOFW-YBXAARCKSA-N
- Assay: ≥98% (enzymatic)
- Form: powder
- Storage Temp.: −20°C