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How do glowing algae (dinoflagellates) chemically create their light?
Question Date: 2001-03-06
Answer 1:

Glowing algae, or bioluminescent algae (most commonly dinoflagellates are the algae responsible for the light) are widespread in the surface waters of most of the world's oceans. They produce a flash of blue-green light whenever the water they are living in is disturbed by motion. You can commonly see bioluminescence from these dinoflagellates at night in breaking waves, in the wake of a boat, and outlining swimming fish or dolphins. Also, if there is a high concentration of these dinoflagellates in the water right off of a beach, sometimes the "dinos" get washed up on the beach and your footprints will glow as you walk along the beach close to the waterline at night. However, dinos only grow to high concentrations during the summer months (most commonly for the temperate waters along the US mainland). It is only when the dinos are in high concentrations that we can see their bioluminescence from the shore, the rest of the time it is too dim to see with your naked eye (unless you are on a very dark beach on a moonless night).

We have created a web site that discusses many of these issues and has pictures and videos of bioluminescent creatures. Please see http://www.lifesci.ucsb.edu/~biolum/ for more general information on bioluminescence.

For how the dinos create the light, you should visit the portion of the web site that discusses the Chemistry of the bioluminescent reaction. There is an animated image that shows some of the bioluminescent reaction mechanisms on this web site that may help you understand the chemistry that underlies bioluminescence. (NOTE: the top figure is the one that applies to the dinoflagellate bioluminescence.)

A few key facts first on the chemistry of dinoflagellate bioluminescence:
- Luciferin is NOT a protein, it is a complex molecule that does not fall into any of the common groups of compounds (luciferin is similar to chlorophyll).
- Luciferase IS a protein. It is an enzyme (more below). Hint: enzymes almost always end in -ase.
- The reactants in the chemical reaction are: luciferin and oxygen (notice: NOT luciferase)
- Luciferase is an assistant for the reaction, like all enzymes, it speeds up the reaction but does not actually take part in the reaction.
- The bioluminescent reaction in dinoflagellates is an ENZYMATIC REACTION (that is, one that requires an enzyme to proceed at a useful rate).

The bioluminescent reaction itself is an oxidation reaction because it involves oxygen and the oxygen reacts with a "substrate", i.e., luciferin. The oxygen oxidizes the luciferin by adding oxygen molecules to the luciferin. This addition of oxygen molecules to the luciferin is assisted by the luciferase enzyme. This reaction is very fast and fairly efficient.

- The product of the reaction is oxyluciferin (luciferin with oxygens attached).
- The bioluminescent light that is emitted when the luciferin is oxidized is a byproduct of the reaction. Also, this light is called, "cold light" because there is almost no heat that accompanies the emission of light.

It is thought that this reaction was NOT initially evolved to produce light, but rather it was a mechanisms of binding up excess oxygen. Excess oxygen, particularly when it is in radical form (not paired with another oxygen atom and having an one excess electron) cause great damage to cells, so it is vital that all cells have mechanisms of getting rid of oxygen radicals (betacarotene is the most common example you hear about in humans, it is an antioxidant, it scavenges oxygen radicals). However, the luciferin-oxidation reaction was probably "switched" to serve the purpose of emitting light as its primary function millions of years ago.

The exact details of how this reaction results in light emission is not completely understood, but basically it is something like this... the oxidation of luciferin is an energy releasing reaction, the energy that is released during this reaction is given off in the form of blue-green light = bioluminescence.

Corrections to a few common misconceptions:

Luciferase does NOT break down luciferin or luciferase.

Luciferin is the most important part of the bioluminescent reaction. It is the molecule that is emitting the light. If there was no luciferin you would have no bioluminescence. LuciferASE is just a helper molecule that assists in the light-emitting reaction.

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