Luciferin

This is a space-filling model of firefly luciferin. Color coding: yellow=sulfur; blue=nitrogen; black=carbon; red=oxygen; white=hydrogen.

Luciferin (from the Latin lucifer, "light-bringer") is a generic term for the light-emitting compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalysed oxidation and the resulting excited state intermediate emits light upon decaying to its ground state. This may refer to molecules that are substrates for both luciferases and photoproteins.

Types

This structure of firefly luciferin is reversed (left to right) from the space-filling model shown above

Luciferins are a class of small-molecule substrates that are oxidized in the presence of the enzyme luciferase to produce oxyluciferin and energy in the form of light. It is not known just how many types of luciferins there are, but some of the better-studied compounds are listed below. There are many types of luciferins, yet all share the use of reactive oxygen species to emit light.

Firefly

Main article: Firefly luciferin

Firefly luciferin is the luciferin found in many Lampyridae species. It is the substrate of luciferase (EC 1.13.12.7) responsible for the characteristic yellow light emission from fireflies. The chemistry is unusual, as adenosine triphosphate (ATP) is required for light emission.

Latia luciferin

Snail

Latia luciferin is, in terms of chemistry, (E)-2-methyl-4-(2,6,6-trimethyl-1-cyclohex-1-yl)-1-buten-1-ol formate and is from the freshwater snail Latia neritoides.

Bacterial

Bacterial luciferin

Bacterial luciferin is a type of luciferin found in bacteria, some of which live within the specialized tissues of some squid and fish. It consists of a long-chain aldehyde and a reduced riboflavin phosphate.

Coelenterazine

Main article: Coelenterazine

Coelenterazine

Coelenterazine is found in radiolarians, ctenophores, cnidarians, squid, brittle stars, copepods, chaetognaths, fish, and shrimp. It is the prosthetic group in the protein aequorin responsible for the blue light emission.

Dinoflagellate

Dinoflagellate luciferin is a chlorophyll derivative and is found in some dinoflagellates, which are often responsible for the phenomenon of nighttime glowing waves (historically this was called phosphorescence, but is an imprecise term). A very similar type of luciferin is found in some types of euphausiid shrimp.

Vargulin

Main article: Vargulin

Vargulin is found in certain ostracods and deep-sea fish, to be specific, Poricthys. Like the compound coelenterazine, it is an imidazopyrazinone and emits primarily blue light in the animals.