Briefly, 10 µL of a working solution containing 2.5 nM hDAO (TECC-1280-14AA, Takeda) and 125 µM FAD (F6625, Sigma) in assay buffer was added to all the wells in the assay ready plate (containing 250 nL compound / DMSO vehicle per well) except for the negative control wells. 10 µL of 125 µM FAD (working solution) was added to the negative control wells containing 250 nL of DMSO vehicle. The plates were incubated at 25˚C for 20 minutes (pre-incubation of compound with human DAO).