page_title: Bioluminescence
section_title: Chemical mechanism
hierarchical_section_title: Bioluminescence / Chemical mechanism
caption_attribution_description: Crystal structure of Photinus pyralis firefly luciferase as published in the Protein Data Bank (PDB: 1LCI)
context_page_description: Bioluminescence is the production and emission of light by a living organism. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some bioluminescent bacteria, 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 a general sense, the principal chemical reaction in bioluminescence involves a light-emitting molecule and an enzyme, generally called luciferin and luciferase, respectively. Because these are generic names, luciferins and luciferases are often distinguished by including the species or group, i.e. firefly luciferin. In all characterized cases, the enzyme catalyzes the oxidation of the luciferin.
  In some species, the luciferase requires other cofactors, such as calcium or magnesium ions, and sometimes also the energy-carrying molecule adenosine triphosphate.
context_section_description: Bioluminescence is a form of chemiluminescence where light energy is released by a chemical reaction. This reaction involves a light-emitting pigment, the luciferin, and a luciferase, the enzyme component. Because of the diversity of luciferin/luciferase combinations, there are very few commonalities in the chemical mechanism. From currently studied systems, the only unifying mechanism is the role of molecular oxygen, which provides chemical energy; often there is a concurrent release of carbon dioxide (CO₂). For example, the firefly luciferin/luciferase reaction requires magnesium and ATP and produces CO₂, adenosine monophosphate (AMP) and pyrophosphate (PP) as waste products. Other cofactors may be required, such as calcium (Ca²⁺) for the photoprotein aequorin, or magnesium (Mg²⁺) ions and ATP for the firefly luciferase. Generically, this reaction can be described as: 
  Luciferin + O₂Oxyluciferin + light energy
  Instead of a luciferase, the jellyfish Aequorea victoria makes use of another type of protein called a photoprotein, in this case specifically aequorin. When calcium ions are added, rapid catalysis creates a brief flash quite unlike the prolonged glow produced by luciferase. In a second, much slower step, luciferin is regenerated from the oxidized (oxyluciferin) form, allowing it to recombine with aequorin, in preparation for a subsequent flash. Photoproteins are thus enzymes, but with unusual reaction kinetics. Furthermore, some of the blue light released by aequorin in contact with calcium ions is absorbed by a green fluorescent protein, which in turn releases green light in a process called resonant energy transfer.
  Overall, bioluminescence has arisen over 40 times in evolutionary history. In evolution, luciferins tend to vary little: one in particular, coelenterazine, is the light emitting pigment for nine phyla (groups of very different organisms), including polycystine radiolaria, Cercozoa (Phaeodaria), protozoa, comb jellies, cnidaria including jellyfish and corals, crustaceans, molluscs, arrow worms and vertebrates (ray-finned fish). Not all these organisms synthesize coelenterazine: some of them obtain it through their diet. Conversely, luciferase enzymes vary widely and tend to be different in each species.
caption: Protein structure of the luciferase of the firefly Photinus pyralis. The enzyme is a much larger molecule than luciferin.
exif: {}