A. Potency distribution (pAC50) for four prominent chemotypes found to inhibit FLuc from profiling efforts. Shown are benzthiazoles (i), benzimidazoles (ii), benzoxazoles (iii), and 3,5-diaryl-oxadiazoles (iv). B. Comparison of FLuc and Ultra-Glo luciferase against a 2-phenylbenzothiazole luciferase inhibitor at multiple substrate concentrations. Graphs of ATP variation (main) or D-LH2 variation (inset) are shown and were varied at 0.25, 2, 25, and 250 μM, resulting in four sets of CRCs. In each case, the constant substrate was present at 250 μM. The FLuc data is shown as solid circles and the Ultra-Glo luciferase is shown as open circles. Simple benzthiazoles appear to be purely competitive with D-LH2 for either luciferase as seen from the right shift of the CRCs (decrease in potency). C. Difference in potency distribution between inhibitors identified in a commercial formulation of FLuc (PK-Light™) and a commercial formulation of Ultra-Glo (KinaseGlo™), illustrating how the source of luciferase reagent can affect in vitro assay interference. D. Comparison of FLuc and Ultra-Glo luciferase inhibition potencies for quinoline analogs assayed using KM levels of substrates. CRCs with for quinolines i (squares) and ii (circles) are shown for FLuc (solid shapes and dotted lines) and Ultra-Glo luciferase (open shapes and solid lines). Selectivity between the two luciferases is observed for such quinolines. Figures adapted from (Auld et al., 2008a; Auld et al., 2009b).