Monitoring the activity of Caspases – a group of cystein-aspartic acid peptidases – is a key method in apoptosis research. The assays are designed around specific peptide substrates for Caspase 3, 7, 8 and 9 respectively which will be cleaved when Caspases are present indicating cells are in an apoptotic state.
Assay technologies are available with luminescent readout through the release of Luciferin which acts as the substrate for the subsequent light generating Luciferase reaction.
Other setups release fluorescent dyes, e.g. Fluorescein or Coumarin derivatives, upon cleavage or coloured substances detectable with absorbance measurements.
Finally there are substrates labelled with lanthanide chelates and quenchers which are cleaved off by the Caspases making the time-resolved fluorescence emission detectable.