Luciferin

Luciferins (the term goes back to the Frenchman Raphael Dubois) are different natural "luminescent substances" which are used by different organisms to produce light (bioluminescence). Through catalytic activities of an enzyme (luciferase enzyme; best studied is the luciferase of the firefly) the luciferins are oxidized. In this oxidative process, energy is usually released in the form of light by splitting off molecules on the luciferin. Both luciferins and luciferases are species- or taxon-specific and are specific for each group of versh. organisms.
The luciferase often catalyzes luciferin with the participation of cofactors such as ATP, under oxygen consumption. The oxidized luciferin is initially in a transitional state, then - often after decarboxylation and further intermediate steps - it reaches an electronically excited state. This excited state returns to its ground state after a very short time (nanoseconds). During this reaction, the substance emits a light quantum. Luciferins are often also fluorophores, i.e. they can also be converted into an excited state by light or UV irradiation.
Bioluminescent systems are evolutionary not conserved. The luciferases and their substrates, the lucerferins, have completely different chemical structures in different groups of organisms. Phylogenetic studies show that luciferin-luciferase systems have > 30 independent origins. Apparently they were often "invented".

The process of bioluminescent excitation is highly energetic. For the emission of photons with a wavelength of e.g. 500 nm (green, energy about 2 eV/photon) about 250 kJ/mol are needed. In comparison, the hydrolytic cleavage of ATP to ADP and phosphate requires about 30 kJ/mol.

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