This unlabeled phosphopeptide is an excellent substrate for mammalian protein tyrosine phosphatase 1B (Km = 3.9 -) and Yersinia PTP. The sequence is derived from an autophosphorylation site (Tyr992) of EGFR. The unlabeled peptide is used to assay PTB based on marked fluorescence increase upon the removal of the phosphate group (Em = 305 nm and Ex = 282 nm).