Ortho-Nitrophenyl-β-galactoside

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ortho-Nitrophenyl-β-galactoside
IUPAC name (2R,3R,4S,5R)-2-(Hydroxymethyl)-6-(2-nitrophenoxy)oxane-3,4,5-triol
Other names 2-Nitrophenylgalactoside
Identifiers
CAS number	369-07-3
PubChem	123646
MeSH	2-nitrophenylgalactoside
Jmol-3D images	Image 1
SMILES O=[N+]([O-])C1=CC=CC=C1O[C@@H]2O[C@H](CO)[C@H](O)[C@H](O)[C@H]2O
Properties
Molecular formula	C12H15NO8
Molar mass	301.249
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

ortho-Nitrophenyl-β-galactoside (ONPG) is a colorimetric and spectrophotometric substrate for detection of beta-galactosidase activity. This compound is normally colorless. However if β-galactosidase is present, it hydrolyzes the ONPG molecule into galactose and ortho-nitrophenol. The latter compound has a yellow color that can be used to check for enzyme activity by means of a colorimetric assay (at 420 nm wavelength). β-galactosidase is required for lactose utilization, so the intensity of the color produced can be used as a measure of the enzymatic rate.

Though ONPG mimics lactose and is hydrolyzed by β-galactosidase, it is unable to act as an inducer for the lac operon. Without another lactose analog that can act as an inducer, such as IPTG, β-galactosidase will not be transcribed and ONPG will not be hydrolyzed.

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