Scintillation Proximity Assay (SPA) Technology to Study Biomolecular Interactions

Abstract

Scintillation proximity assay (SPA) is a versatile homogeneous technique for radioactive assays which eliminates the need for separation steps. In SPA, scintillant is incorporated into small fluomicrospheres. These microspheres or “beads” are constructed in such a way as to bind specific molecules. If a radioactive molecule is bound to the bead, it is brought into close enough proximity that it can stimulate the scintillant contained within to emit light. Otherwise, the unbound radioactivity is too distant, the energy released is dissipated before reaching the bead, and these disintegrations are not detected. In this unit, the application of SPA technology to measuring protein‐protein interactions, Src Homology 2 (SH2) and 3 (SH3) domain binding to specific peptide sequences, and receptor‐ligand interactions are described. Three other protocols discuss the application of SPA technology to cell‐adhesion‐molecule interactions, protein‐DNA interactions, and radioimmunoassays. In addition, protocols are given for preparation of SK‐N‐MC cells and cell membranes.