Description_x000D_ Application_x000D_ 4-Nitrophenyl phosphate disodium salt hexahydrate has been used in enzyme-linked immunosorbent assay (ELISA) as a substrate for streptavidin-Alkaline Phosphatase. It has also been used as a substrate in control assay for comparing 4-aminophenyl phosphate/diethanolamine (APP/DEA) assay for alkaline phosphatase._x000D_ Chromogenic substrate for the determination of acid and alkaline phosphatases. The reaction produces a soluble end product that is yellow in color. The reaction may be stopped with 3 N NaOH and read at 405 nm._x000D_ Biochem/physiol Actions_x000D_ 4-Nitrophenyl phosphate disodium salt hexahydrate (pNPP) is a non-proteinaceous and non-specific substrate for determining protein tyrosine phosphatase activity. Hydrolysis of pNPP yields p-nitrophenol. pNPP is a common chromogenic substrate for alkaline phosphatase._x000D_ Quantity_x000D_ Contains 15 mg substrate per tablet