Protein phosphatase, enzyme that control the removal of phosphate (PO43-) group from protein molecules, regulates many fundamental cellular process such as cell attachment, proliferation, differentiation and apoptosis. ScienCell pNPP Phosphatase Assay is optimized to detect phosphatase activity in biological samples using pNPP (4-nitrophenyl phosphate) as a colorimetric substrate for most phosphatases. A water soluble yellow product with a strong absorption at 405 nm is developed during the reaction of pNPP with phosphatase and can be detected with an ELISA plate reader.