Luciferins

Luciferins are a group of small organic molecules that act as substrates for bioluminescence. In organisms that produce light, luciferin is oxidized by a luciferase enzyme, often in the presence of cofactors, and the energy released is emitted as photons. The term covers many chemically distinct compounds; different taxa use different luciferins.

In insects such as fireflies and some beetles, the substrate is D-luciferin. The luciferase-catalyzed reaction requires ATP and oxygen and proceeds via formation of a luciferin-adenylate intermediate, oxidation to an excited-state product, and photon emission. The resulting light is typically yellow to green, depending on the system.

In marine and some other organisms, coelenterazine is a common luciferin. It emits blue light when oxidized by various luciferases, for example Renilla or those from jellyfish. Marine systems can use different luciferins and enzymes, yielding a range of emission spectra. Other fungi, dinoflagellates, and bacteria also employ distinct luciferin-like compounds; the chemical diversity among luciferins is high.

Bioluminescence depends on the interaction of luciferin with luciferase and, in many systems, requires oxygen and, in the firefly system, ATP as an energy source. The emission color, intensity, and efficiency depend on the specific luciferin–luciferase pair and environmental conditions.

Applications include the use of luciferins in biotechnology and research as reporters for gene expression, cell imaging, and assay development. D-luciferin is commonly used with firefly luciferase for in vivo imaging in mammals; coelenterazine-based systems provide alternative reporters with different emission spectra, enabling multi-reporter experiments.