When I took a physiology class in college, we performed various experiments. Among them was a demonstration of firefly lightning in which we mixed luciferin with luciferase and produced the yellow glow of bioluminescence.
Recently, we toured the Franklin Museum in New Jersey and its associated Sterling Mine in Ogdensburg, which closed in 1986. The mine sits on one of the largest zinc deposits on Earth, and closed only because the price of zinc had fallen severely and was no long economical to operate.
Today, the Sterling Mine has tours that include a collection of mining memorabilia. The Franklin Museum houses a large collection of minerals, many locally sourced — but most importantly, many are beautifully fluorescent.
A definition of terms will be useful.
Chemiluminescence is the emission of light, sometimes with minimal heat emission, as a result of a chemical reaction. Glow sticks work, for example, through such an internal reaction. The chemicals are used up over time, the reaction runs down, and the light vanishes.
Bioluminescence is a subset of chemiluminescence in that the chemical reaction takes place within a living organism (albeit without any emission of heat).
Whereas fluorescence also creates glowing light, it is an entirely different process. It is an effect produced by the impact of high-energy light of differing wavelengths upon a material (which can be either organic or inorganic) that is then re-transmitted as lower-energy wavelengths.
The typical types of incident light used are ultraviolet, X-rays and cathode ray tubes (the wavelengths of which overlap those in the UV range). Impacted molecules have their energy levels raised to an unstable state, and the new wavelength is emitted when the molecule returns to its more stable condition (its original state).
The resulting fluorescence is of a longer and lower-energy wavelength than that of the impacting light.
There are more fluorescent minerals in the Franklin-Sterling Hill area than anywhere else in the world. Different minerals fluoresce best at different wavelengths.
The minerals at the Franklin Museum are divided into three categories based on the ultraviolet wavelengths to which they respond: shortwave ultraviolet radiation, mid-wave ultraviolet radiation, and long-wave ultraviolet radiation. The wavelength spectrum of light visible to the human eye is 380 to 740 nanometers, which is beyond long-wave ultraviolet radiation.
Some of the Franklin minerals phosphoresce as well as fluoresce, and the phosphorescence can be long- or short-lived depending on the particular mineral.
Phosphorescence can be categorized as a longer-lasting type of fluorescence. This is so because the molecules impacted by high-energy light are more stable than those that only fluoresce, so the new wavelengths are emitted more slowly as the excited state gradually returns to its original and most stable energy level.
To summarize, fluorescence and phosphorescence require energy input from the outside in the form of high-energy light waves, while bioluminescence is an internal process requiring the presence of specialized chemicals and structures.
Luciferins, from the Latin lucifer or “light-bringer,” are the compounds which generate light when activated by the luciferase enzymes.
Generally proteins, the enzymes are an essential part of biological systems, which speed up chemical reactions without themselves being changed or used up.
Without them, many of the chemical reactions necessary for life would occur too slowly for biological organisms to survive.
Bioluminescence can be found over wide swaths of living creatures, particularly marine animals including fish, jellyfish, crustaceans and dinoflagellates (a photosynthetic plankton, some members of which also eat living prey). It can also be found in insects other than fireflies, such as click beetles (family elateridae) and railroad worms (genus Phrixothrix).
Many bacteria and fungi also demonstrate this phenomenon.
Despite the breadth of organisms involved, there are just relatively few luciferins. Coelenterazine is probably the most widespread luciferin found in many marine organisms, including squid, brittle stars and cnidarians (a phylum including jellyfish).
Dinoflagellates have their unique luciferin, which is similar to the chlorophyll molecule and may be derived from it. They seem to be responsible for the phenomenon known as “mareel,” which is a spectacular flashing and sparkling of blue luminescence seen in waves at night, particularly in the Indian Ocean.
Mareel derives from Norn (a Norse language spoken in Orkney Islands from the time of the Vikings) word marled, itself derived from Old Norse morueldr from marr, which is “sea,” and eldr, which is “fire.”
Vargula luciferin is found in certain ostracods (class Crustacea) known as seed shrimp. The fish Porichthys notatus is only luminescent if it eats marine organisms such as the ostracods that contain the Vargula luciferase.
There are other luciferins that are unique to bacteria and fireflies. But we will continue more on that next time.
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