para-Nitrophenylphosphate

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para-Nitrophenylphosphate
Skeletal formula of para-nitrophenylphosphate
Space-filling model of the para-nitrophenylphosphate molecule
Names
IUPAC name
(4-nitrophenyl) dihydrogen phosphate
Other names
pNPP
Identifiers
3D model (Jmol)
ChEBI
ChemSpider
ECHA InfoCard 100.005.777
Properties
C6H6NO6P
Molar mass 219.088701
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

para-Nitrophenylphosphate (pNPP) is a chromogenic substrate for acid and alkaline phosphatase in ELISA and conventional spectrophotometric assays. These enzymes catalyse the hydrolysis of pNPP to yellow para-nitrophenol. This product absorbs strongly at 405 nm and can be measured with a visible light spectrophotometer and mainly used in the study of kinetics of enzyme-substrate catalysis reaction catalysed by alkaline phosphatase enzyme in accordance with Lineweaver-Burk formula.Activity assays of alkaline phosphatase with p-nitrophenyl phosphate are terminated by the addition of NaOH. This serves two functions; first, it stops the enzyme-catalysed reaction by changing pH which is unsuitable for the enzyme (the enzyme is denatured at high pH and so unable to function). Second, it deprotonates the p-nitrophenol to give the yellow coloured p-nitrophenylate. The progress of the reaction is monitored by absorption spectrum of p-nitrophenolate (obtained upon deprotonation of p-nitrophenol).

PNPP+H2O → PNP + inorganic phosphate

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