Firefly luciferin in the context of "Bioluminescence"

Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some bioluminescent bacteria, dinoflagellates and terrestrial arthropods such as fireflies. In some animals, the light is bacteriogenic, produced by symbiotic bacteria such as those from the genus Vibrio; in others, it is autogenic, produced by the animals themselves.

In most cases, the principal chemical reaction in bioluminescence involves the reaction of a substrate called luciferin and an enzyme, called luciferase. Because these are generic names, luciferins and luciferases are often distinguished by the species or group, e.g. firefly luciferin or cypridina luciferin. In all characterized cases, the enzyme catalyzes the oxidation of the luciferin resulting in excited state oxyluciferin, which is the light emitter of the reaction. Upon their decay to the ground state they emit visible light. In all known cases of bioluminescence the production of the excited state molecules involves the decomposition of organic peroxides.