Figure 1.

HPLC profiles obtained following the incubation of (A) PYY(1-36), (B) (P³L³¹P³⁴)PYY(1-36), and (C) PYY(1-36)(Lys¹²PAL) with purified DPP-4. Peptides (50 µg; n = 3) were incubated at 37°C with 5 µL DPP-4 enzyme (0.01 U/µL) in 50 mM triethanolamine-HCl. Reactions were stopped using 10% (v/v) trifluoroacetic acid/water and reaction mixes separated by HPLC. Peptide or peptide fragment masses were determined by MALDI-TOF MS (see Supplementary Data). DPP-4 indicates dipeptidyl peptidase-4; HPLC, high-performance liquid chromatography; MALDI-TOF MS, matrix-assisted laser desorption ionisation time-of-flight mass spectrometry; PYY, peptide tyrosine tyrosine.