Fig. 1. Solution-based assays coarse-grain reaction mechanisms for the tyrosine phosphatase SHP-1.

(A) Schematic of the domain structure of SHP-1 and a subset of reactions that may occur in solution with peptide substrates. (B) Standard solution–based enzymatic assay showing the production of inorganic phosphate (product) over time for the indicated concentration of SHP-1 mixed with the PEG12-ITIM substrate (data are representative of two independent experiments). Progress curves are fit with a mathematical model to provide an estimate for ${\mathit{k}}_{\text{cat}}^{*}$ (see Materials and Methods).