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N1127 Sigma

2-Nitrophenyl β-D-galactopyranoside

≥98% (enzymatic)

Synonym: o-Nitrophenyl β-D-galactopyranoside, ONPG


General description

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


1 g in poly tube

250 mg in poly bottle

5, 25 g in poly bottle

500 mg in poly tube


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.

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