ortho-Nitrophenyl-β-galactoside
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| Ortho-Nitrophenyl-β-galactoside | |
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| IUPAC name | (2R,3R,4S,5R)-2-(Hydroxymethyl)-6-(2-nitrophenoxy)oxane-3,4,5-triol |
| Other names | 2-Nitrophenylgalactoside |
| Abbreviations | ONPG |
| Identifiers | |
| CAS number | [19710-96-4] |
| PubChem | |
| MeSH | |
| 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 disclaimer and references |
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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 coloration that can be used to check for enzyme activity by means of a colorimetric assay.
Beta-galactosidase is required for lactose utilization, so the intensity of the color produced can be used as a measure of the rate that Beta-galactosidase can hydrolyze lactose.
Though ONPG mimics lactose and is hydrolysed by Beta-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, Beta-galactosidase will not be transcribed and ONPG will not be hydrolyzed.
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