Elution profiles of DPP4 chromatography. (A) Chromatogram from Phenyl Sepharose that was equilibrated with 12% ammonium sulphate (AS) in 10 mM Tris-HCl pH 7.6 and eluted with 0% AS in 10 mM Tris-HCl pH 7.6 buffer. Inset: Fibroblast activation protein (FAP) activity. (B) Chromatogram from Nickel Sepharose, which was equilibrated with 20 mM imidazole in 200 mM NaCl, 10 mM Tris-HCl, pH 7.6 and eluted with an increasing concentration gradient of imidazole at 30 mM (a), 100 mM (b), 500 mM (c), 1000 mM (d) in 10 mM Tris-HCl pH 7.6 buffer. Inset: FAP activity. (C) Chromatogram from DEAE Sepharose that was equilibrated with 10 mM Tris-HCl pH 7.6 and eluted with 200 mM NaCl in 10 mM Tris-HCl pH 7.6 buffer. Inset: sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE; 4–12% Bis-Tris gel) of the resulting purified soluble DPP4, stained with Sypro ruby Protein was measured by optical density at 280 nm in these chromatograms.