The PathHunter Bioassay Detection Kit is to be used with PathHunter Bioassay cells or PathHunter Cell Lines. The kit is easy-to-use and has been successfully run in a 96-well microplate format. The resulting signal is chemiluminescent and is read with any standard plate reader. PathHunter products utilize the Enzyme Fragment Complementation (EFC) technology for studying protein-protein interactions, protein translocation, receptor trafficking, and receptor internalization, all of which involve the complementation of two β-galactosidase (β-gal) fragments. The larger β-gal fragment is called Enzyme Acceptor (EA) and the smaller fragment is termed Enzyme Donor (ED; also known as ProLabel® or ProLink™). The two fragments are inactive when apart. However, when they complement, they form a functional enzyme that hydrolyzes the substrate to generate a chemiluminescent signal. The detection reagents do not contain either the EA or ED fragments of β-gal, and therefore must be used in conjunction with cells that express both components in order to obtain a detectable signal.