''para''-Nitrophenylphosphate (pNPP) is a non-proteinaceous
chromogenic substrate
In chemistry, the term substrate is highly context-dependent. Broadly speaking, it can refer either to a chemical species being observed in a chemical reaction, or to a surface on which other chemical reactions or microscopy are performed.
In the ...
for
alkaline and acid phosphatases used in
ELISA
The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay (EIA) to detect the presence ...
and conventional spectrophotometric assays. Phosphatases catalyze the hydrolysis of pNPP liberating inorganic phosphate and the conjugate base of
''para''-nitrophenol (pNP). The resulting phenolate is yellow, with a maximal absorption at 405 nm. This property can be used to determine the activity of various phosphatases including alkaline phosphatase (AP) and protein tyrosine phosphatase (PTP).
The substance is sensitive to light, and thus should be stored protected from light. This is also important after adding the substrate to the mixture and before reading. −20 °C is the optimal storage temperature.
References
External links
pNPP disodium salt hexahydrate (SigmaAldrich.com)
Organophosphates
Nitrobenzenes
Phenol esters
{{Organic-compound-stub