Fig. 2.

The condensates of oABA with delta-1-pyrroline (THPQ) or delta-1-piperideine (HHPQ) are not only quinazoline chromophores but also novel fluorophores. Two µg/ml purified rhDAO in 20 mM Hepes (pH 7.0) containing 0.05% human serum albumin (HSA) was incubated for 2 h at 37 °C with 1 mM ortho-aminobenzaldehyde (oABA) and 400 µM putrescine, cadaverine, histamine or Hepes buffer followed by ultrafiltration using a 3 kDa MWCO device; a Absorption (ABS) was measured from 300 to 700 nm after fivefold dilution using water in UV-compatible half-area plates; b Specific absorption curves after subtracting the Hepes buffer control data; c Fluorescence emission was measured between 500 and 700 nm after excitation at 460 nm; d Fluorescence emission was measured at 620 nm after excitation between 360 and 560 nm; White squares (□) represent cadaverine as substrate; White triangles (Δ) putrescine; White circles (○) histamine and black line (▬) no substrate. MWCO  molecular weight cut-off, RFU relative fluorescence units