Representative corepressor competition data. This plot shows the background-subtracted and normalized fluorescence as a function of SMRT (●) and NCoR (○) concentrations obtained at 5 μM F-SRC-1, in the absence of ligand. Background fluorescence, measured in the absence of surface-immobilized PXR-LBD, was subtracted, and the data were fit to eq 8 with QS and Kd′ as free parameters and using the following fixed parameters: A = 5 μM, and Kd = 5 μM. Equilibrium dissociation constants of 65 ± 13 and 200 ± 50 μM were obtained for the SMRT–PXR-LBD (●) and NCoR–PXR-LBD (○) interactions, respectively. These data were normalized to fluorescence counts determined using the value of the fit parameter QS, A = 5 μM, Kd = 5 μM, and B = 0 μM (no corepressor). The data are averages of two trials, and the errors are the corresponding standard deviations.