Firefly luciferin (also known as beetle luciferin) is the

luciferin Luciferin () is a generic term for the light-emitting chemical compound, compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with Oxygen, molecular oxygen. The resulting transforma ...

, precursor of the light-emitting compound, used for the

firefly The Lampyridae are a family of elateroid beetles with more than 2,000 described species, many of which are light-emitting. They are soft-bodied beetles commonly called fireflies, lightning bugs, or glowworms for their conspicuous production ...

( Lampyridae), railroad worm ( Phengodidae), starworm ( Rhagophthalmidae), and click-beetle ( Pyrophorini) bioluminescent systems. It is the substrate of firefly luciferase ( EC 1.13.12.7), which is responsible for the characteristic light emission of many

and other insect species in the visible spectra ranging from 530 until 630 nm. As with other luciferins, oxygen is essential for the

luminescence Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. A luminescent object emits ''cold light'' in contrast to incandescence, where an obje ...

mechanism, which involves the decomposition of a cyclic

peroxide In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...

to produce excited-state molecules capable of emitting light as they relax to the

ground state The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state ...

. Additionally, it has been found that

adenosine triphosphate Adenosine triphosphate (ATP) is a nucleoside triphosphate that provides energy to drive and support many processes in living cell (biology), cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known ...

(ATP) and

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

are required for light emission.

History

Much of the early work on the chemistry of the firefly luminescence was done in the lab of William D. McElroy at

Johns Hopkins University The Johns Hopkins University (often abbreviated as Johns Hopkins, Hopkins, or JHU) is a private university, private research university in Baltimore, Maryland, United States. Founded in 1876 based on the European research institution model, J ...

. The luciferin was first isolated and purified in 1949 from a large amount of specimens, though it would be several years until a procedure was developed to crystallize the compound in high yield. This, along with the synthesis and structure elucidation, was accomplished by Dr. Emil H. White at the Johns Hopkins University, Department of Chemistry. The procedure was an acid-base extraction, given the

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

group on the luciferin. The luciferin could be effectively extracted using

ethyl acetate Ethyl acetate commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This flammable, colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues, nail polish removers, ...

at low pH from powder of approximately 15,000 firefly lanterns. The structure was later confirmed by combined use of

infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functio ...

, UV–vis spectroscopy and synthetic methods to degrade the compound into identifiable fragments.

Properties

Crystal luciferin was found to be

fluorescent Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with color ...

, absorbing

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

light with a peak at 327 nm and emitting light with a peak at 530 nm. Visible emission occurs upon relaxation of the oxyluciferin from a singlet excited state down to its ground state. Alkaline solutions caused a

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...

of the absorption likely due to deprotonation of the

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

group on the benzothiazole, but did not affect the fluorescence emission. It was found that the luciferyl adenylate (the AMP

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

of luciferin) spontaneously emits light in solution. Different species of fireflies all use the same luciferin, however the

color Color (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...

of the light emitted can differ greatly. The light from '' Photuris pennsylvanica'' was measured to be 552 nm (green-yellow) while '' Pyrophorus plagiophthalamus'' was measured to emit light at 582 nm (orange) in the ventral organ. Such differences are likely due to pH changes or differences in

primary structure Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthe ...

of the luciferase. Modification of the firefly luciferin substrate has led to "red-shifted" emissions (up to emission wavelength of 675 nm).

Biological activity

The

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...

synthesis of firefly luciferin is not completely understood. Only the final step of the enzymatic pathway has been studied, which is the

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

of D-

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

with 2-cyano-6-hydroxybenzothiazole, and is the same reaction used to produce the compound synthetically. This was confirmed by

radiolabeling A radioactive tracer, radiotracer, or radioactive label is a synthetic derivative of a natural compound in which one or more atoms have been replaced by a radionuclide (a radioactive atom). By virtue of its radioactive decay, it can be used to exp ...

of atoms in the two compounds and by identification of a ''luciferin-regenerating enzyme''. In

, oxidation of luciferins, which is catalyzed by luciferases, yields a peroxy compound 1,2-dioxetanone. The dioxetanone is unstable and via the release of

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

and excited

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

s, which release excess energy by emitting light (

bioluminescence Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorgani ...

Firefly luciferin and modified substrates are fatty acid mimics and have been used to localize fatty acid amide hydrolase (FAAH) ''in vivo.'' Firefly luciferin is a substrate of the ABCG2 transporter and has been used as part of a bioluminescence imaging high throughput assay to screen for inhibitors of the transporter.

References

{{reflist, 30em

External links

Bioluminescence Page
showing major luciferin types Benzothiazoles Biochemical reactions Bioluminescence Carboxylic acids Thiazolines Luciferins