Determination of equilibrium dissociation constants in fluorescence polarization

A simple mathematical model (the FP K-d model) is used to generate the diss ociation equilibrium constant (K-d) for G protein-coupled receptor-ligand b inding measured using fluorescence polarization (FP) saturation curve analy sis. The model generates data that may be analyzed by the method of Scatcha rd. The validity of the FP K-d model is proven in six model systems in whic h the modeled K-d values are within a factor of 5 of inhibitory equilibrium constant values obtained from radioligand competition assays.