A sensitive bioluminescent assay to detect proteases, including caspases and proteases that specifically cleave a peptide substrate having aspartate, is provided. In one embodiment, the assay employs an aminoluciferin or a carboxy-terminal protected derivative thereof covalently linked via a peptide bond to a substrate for a caspase or an aminoluciferin or a carboxy-terminal protected derivative thereof covalently linked via a peptide bond to a peptide substrate comprising aspartate that is specifically cleaved by a protease specific for the substrate.