ONPG
Product Code: EN06363
CAS Number: 369-07-3
Chemical Formula: C 12 H 15 NO 8
Molecular Weight: 301.25
OH
HO
OO
OH
O
Synonyms: 2-Nitrophenyl β-D-galactopyranoside
N
+
O
OH
ONPG is the common abbreviation for ortho-Nitrophenyl-β-D-galactopyranoside.
ONPG is used in colourimetric and spectrophotometric assays for the detection of βgalactosidase activity which are of interest in clinical, environmental, food and molecular biology
arenas.1 ONPG is hydrolysed by β-galactosidase to yield galactose and ortho-Nitrophenol, which
is yellow in colour and absorbs light at 420 nm. The intensity of the colour can be used to
determine the rate at which β-galactosidase can hydrolyse lactose. The impact of experimental
factors on the reproducibility of β-galactosidase assays has been reported.2
OH
HO
OH
OO
OH
O
N
b-Galactosidase
+
HO
O OH
OH
O
OH
ONPG
+
OH
HO
O
N
+
O
ortho-Nitrophenol
In common with several other β-galactosidase substrates such as X-Gal, ONPG does not act as an
inducer of genes under the control of the lac operon in bacteria such as E. coli. In the absence of
a lactose analogue such as IPTG (Product Code: EI05931) transcription of β-galactosidase will
not take place and ONPG will not be hydrolysed.
References:
1. J Lederberg, J. Bacteriol., 1950, 20, 137.
2. A Giacomini et al, FEMS Microbiol. Lett., 2006, 100, 87.
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