35,000 mouse DAO CHO-K1 transiently transfected cells (20 µL in 10 mM HEPES buffer) were added to all the wells in the assay ready plate (containing 250 nL compound / DMSO vehicle per well). 5 µL of a working solution containing 250 mM D-Serine, 250 µM Amplex Red and 0.625 U/mL HRP in assay buffer was added to all the wells except for the negative control wells. 5 µL of a working solution of 250 µM Amplex Red and 0.625 U/mL HRP in assay buffer was added to the negative control wells. The plate was incubated for 30 minutes in the dark at 25˚C before measuring fluorescence in each well using the Envision plate reader with excitation at 530 nm and emission at 595 nm.