Bioluminescence In Chemistry

2.1 Chemistry of Bioluminescence

Bioluminescence is the production of light as a result of a chemical reaction without the use of heat within a living organism. For bioluminescence to occur usually two substances and a by-product such as oxygen are required. In the majority of bioluminescent reactions, the chemical reaction which leads to bioluminescence is the oxidation of a molecule called luciferin. Luciferin, which is the substrate in this chemical reaction, is the chemical in the reaction which produces light. The reaction rate of this reaction is controlled by an enzyme called Luciferase which acts as a biological catalyst. A catalyst is a chemical which interacts with the substrate in the reaction in order to alter the rate of the chemical

Luciferin

There are four luciferin molecules which are responsible for the occurrence of bioluminescence. However there are many other luciferin molecules which have not yet been discovered to date. The four major luciferin molecules will be described in greater detail below.

Coelenterazine

The most widespread luciferin molecule used in the chemical reaction resulting in bioluminescence is Coelenterazine. The majority of marine organisms use Coelenterazine in the process of bioluminescence. However, the only difference between each organism’s reaction is the type of luciferase each organism uses. Coelenterazine is used along with photo-proteins by Hydrozoans, Ctenophores, and Radiolarians. Coelenterazine is also well known for the fact that it is the light emitter of Aequorin. Aequorin was the first known photo-protein. Bacterial

Bacterial Luminescence consists of the oxidation of a molecule called FMNH2 (a reduced riboflavin phosphate) (see figure 1). This is molecule is oxidised along with oxygen, a long-chain aldehyde, and a two-subunit

This luciferin is a tetrapyrrole and differs to chlorophyll due to the type of metal ions present in its structure. Light emission from Dinoflagellates is pH-sensitive. This is mainly due to two factors. Due to the tertiary structure of the luciferase, a change in H+ ion concentration causes the luciferase to lose conformation, exposing its active site to the luciferin. Also, the luciferin molecule can be protected until the pH is suitable for it to bind to the protein. This can be seen in the genus Gonyaulax, where at pH 8 the luciferin molecule is protected by luciferin-binding protein, but when the the pH lowers to around 6, the free luciferin is released and reacts with the luciferase and therefore producing light.

Ostracod Luciferin

Ostracod Luciferin was one of the first marine luciferins to be chemically understood. Vargulin or Cypridina-type luciferin is the type of luciferin found in the Ostracod, Cypridina, and also Porichthys. Kato et.al (2004,2007) demonstrated that Ostracods synthesize their luciferin from the amino acids tryptophan, isoleucine, and arginine. It has also been found that in Porichthys there is a dietary link , as these fish lose their ability to luminescence unless they are fed luciferin-bearing food.

Other and Novel Luciferin

Apart from the four major luciferins listed above, there are other light emitters from additional taxa. There are many more luciferin