Bioluminescence

Bioluminescence is the emission of light by an organism as a result of a biochemical reaction. In contrast to fl uorescence and phosphorescence, bioluminescence reactions do not require the initial absorption of sunlight or other electromagnetic radiation by a molecule or pigment to emit light. Bioluminescent systems produce light through the oxygenation of a substrate, generically called luciferin (lat. lucifer, the lightbringer), and an enzyme, luciferase. Bioluminescent reactions vary greatly among organisms but can generally be described as a luciferase catalyzed production of an excited intermediate from oxygen and luciferin that emits light when returning to its ground state. Additionally, many bioluminescence systems involve cofactors such as FMNH2, ATP, additional enzymes and intermediate steps for the light production. In some bioluminescence systems special types of luciferases, photoproteins, bind and stabilize the oxygenated luciferin and emit light only in the presence of cations, such as Mg2+ or Ca2+, which acts as a mechanism for the host to precisely control the timing of the light emission.