Bioluminescence
Bioluminescence refers to the light-emitting characteristics of certain living organisms. It is a special type of the more general process, chemiluminescence that relates to the production of light from a chemical reaction. The reaction that creates bioluminescence is generally the same in all organisms. It is a complex one that involves the oxidation of luciferin (a protein) catalyzed by luciferase enzyme.
A wide variety of organisms throughout nature produce light. The most familiar are fireflies and glow worms. However, bioluminescence is more commonly found in marine animals such as jellyfish, dinoflagellates, mollusks, shrimp, octopuses, fish, and sponges. Bacteria and fungi also have species that exhibit bioluminescence. These organisms create bioluminescence in many ways and for different reasons. Fireflies have glowing abdomens, which function in mating. Marine fireworms use bioluminescence for a similar reason. Deep sea fish have organs called photophores which create a center for the bioluminescent reactions. These organs not only help attract mates, they also attract prey and help illuminate the search for food. The angler fish has a photophore located on a long fin which it dangles as a lure in front of its mouth. Other uses of bioluminescence include camouflage and schooling. While it is evident why certain organisms display bioluminescence, some organism such as mushrooms glow for unknown reasons.
As varied as the types of organisms are that produce bioluminescence, so too are the ways that they produce it. Some bacteria and fungi emit light constantly. Other organisms must be stimulated to produce light. Still others produce it only when required. There are various bioluminescent organisms that do not actually produce the light themselves, but have a symbiotic relationship with a luminescent organism. The most common colors are yellow, blue, red, and green. Certain shrimp have developed lenses and color filters which makes their bodies light up in a multicolor fashion.
Bioluminescence is a unique chemical reaction. It is a form of chemiluminescence that involves the generation of light without the production of heat. In these types of reactions the reactants form intermediates which have electrons in an excited state. When the electrons return to a relaxed state, they emit photons and produce light. The wavelength at which the photon is emitted is responsible for the color that is observed. The basic chemical reactions that produce bioluminescence are the same in all organisms. The principal chemicals involved are luciferin, luciferase, oxygen, and adenosine triphosphate (ATP). Most of the research performed to understand these reactions has been done using dried firefly tails.
The firefly luciferin has a chemical formula C13H12N2O3S2. It is an organic compound with a complex ring system. In the presence of ATP and the luciferase enzyme, a complex containing all three is formed. It reacts with oxygen, releasing adenosine monophosphate (AMP), inorganic phosphate, the enzyme, carbon dioxide, and a photon of light. In the firefly, this reaction occurs in an instant flash in the abdomen. Other organisms like bacteria or fungi have a sustained bioluminescence. The sustained effect is a result of the reaction of riboflavin phosphate with oxygen and luciferase.
While the use of bioluminescent materials is limited by their expense, they have been used for certain applications. For example, in many countries, lanterns are made using ground up fireflies. Luciferin and luciferase have been used in biological research, space exploration, and oceanography to detect traces of ATP.
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