ABSTRACT
Receptor binding assays (RBA) encompass a variety of techniques used to study ligand-receptor interactions. Activation of the receptor-ligand complex and its downstream cellular pathway(s) often leads to the changes in cellular function that may be related to a disease phenotype. Understanding this process can lead to the development of new therapeutic agents used to treat a variety of diseases. Scintillation proximity assay (SPA) bead-based technology has been successfully applied to study receptor-ligand binding interactions in a wide range of assays. These beads, which are size excluded to approximately 3 to 5 microns, can be coated with various capture molecules that facilitate the binding of specific biomolecules. The basic principle of SPA employs immobilizing a receptor by a specific capture molecule, typically wheat germ agglutinin (WGA)–coated
SPA beads. Isotopes commonly used with SPA include
P,
C,
S,
H, and
I; the latter two isotopes, tritium and iodine 125, are most commonly used for receptor binding assays. The general concept of a SPA receptor binding assay is depicted in Figure 11.1. Once a specific membrane receptor is bound to the bead, it can be challenged by an appropriate radiolabeled molecule or by a specific competitor. If the radiolabeled molecule or ligand binds to the bead via its receptor, energy from the decaying isotope is transferred to the scintillant within the bead, at which point light will be emitted from the bead, and a specific signal will be detected that is proportional to the amount of radiolabeled compound bound to the bead [1].
