KGaA, Weinheim. Abstract A novel luciferin from a bioluminescent Siberian earthworm Fridericia heliota was recently described. In this study, the Fridericia oxyluciferin was isolated and its structure elucidated. The results provide insight into a novel bioluminescence mechanism in nature. Oxidative decarboxylation of a lysine fragment of the luciferin supplies energy for light generation, while a fluorescent CompX moiety remains intact and serves as the light emitter. Let there be light: The oxyluciferin from the bioluminescent worm Fridericia heliota was isolated and its structure elucidated. The results provide insight into a novel bioluminescence mechanism. Oxidative decarboxylation of a lysine fragment of the luciferin supplies energy for light generation, while a fluorescent CompX moiety remains intact and serves as the light emitter.