A representative in vitro biochemical assay of DPP-2 with recombinant APT1. (a) Normalized in vitro fluorescence assays of 5 μM DPP-2, incubated with or without 50 nM purified APT1 (λex 490/9 nm, λem 545/20 nm) in HEPES Buffer (20 mM, pH 7.4, 150 mM NaCl, 0.1% Triton X-100). Error bars are standard error (n = 3). (b) Normalized fluorescence emission spectrum of 5 μM DPP-2, incubated with or without 50 nM APT1 for 20 min (λex = 485 nm). Spectra are plotted as average of n = 3.