Units Required for Phosphate Removal

Unit assays for protein phosphatases use the organic substrate p-nitrophenyl phosphate, PNPP (NEB #P0757). The reactivity of phosphatases toward phosphorylated protein substrates can be markedly different from that observed with PNPP. Accordingly, removal of an equivalent amount of phosphate groups from a given protein may require a radically different number of PNPP units to be added to the reaction. Because phosphate removal can differ among proteins, the table lists a range between 5 and 10-fold higher than this determined value to ensure complete dephosphorylation.