A novel chemiluminescent substrate for detecting lactamase

β-lactamase is a well established reporter for monitoring cellular events while chemiluminescence is the preferred read-out mode in high throughput screens. Here, we report the first chemiluminescent assay for β-lactamase using β-galactosidase based enzyme fragment complementation technology. The enzyme fragment complementation technology employs a large protein fragment called the enzyme acceptor and a small peptidic fragment called an enzyme donor. These fragments are inactive separately but recombine rapidly in solution to yield active β-galactosidase detected by chemiluminescence or fluorescence. A cyclic enzyme donor comprising a substituted cephalosporin moiety is used as the lactamase substrate. The cyclic substrate does not complement with enzyme acceptor to yield active β-galactosidase, but upon cleavage with lactamase yields the linear enzyme donor which complements readily with enzyme acceptor. This methodology has been exploited in a simple, sensitive, homogeneous cell based reporter gene assay to monitor G-protein coupled receptor activation in a microtitre plate with a chemiluminescent read out.