Coelenterazine is a luminescent enzyme substrate for apoaequorin and Renilla luciferase. Renilla luciferase and substrate coelenterazine have been used as bioluminescence donors in bioluminescence resonance energy transfer (BRET) to detect protein-protein interactions. Coelenterazine is a superoxide anion-sensitive chemiluminescent probe, and it can also be used in the chemiluminescent detection of peroxynitrite.