P0757S, p-Nitrophenylphosphate (PNPP) 500 mM - 1 ml

p-Nitrophenyl Phosphate (PNPP) is a non-proteinaceous, non-specific substrate used to assay protein, alkaline and acid phosphatases. The PNPP phosphatase activity is measured using a continuous or single-point spectrophotometric assay based on the ability of phosphatases to catalyze the hydrolysis of PNPP to p-nitrophenol, a chromogenic product with absorbance at 405 nm. The assay can be used for the quick analysis of the protein phosphatase activity under any non-standard conditions. 

The advantage of the PNPP phosphatase activity assay is that unlike radioactive assays the substrate concentration can be much higher than the K_m. The initial velocity can be recorded in the continuous assay, but the assay volume is larger than in a radioactive assay (about 1 ml to fill a 1 ml spetrophotometer cuvette). The reaction volume in a single-point assay can be very small because the reaction is stopped with the amount of NaOH enough to fill the cuvette.