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iLabs: Visitor Question: Fireflies vs. Plankton, and the Colors They Emit

August 14, 2012

This weekend’s visitor question has to do with fireflies, plankton, and bioluminescence:

Fireflies, which are bioluminescent, glow yellow at night. Our Pyrocystis fusiformis, the bioluminescent plankton in our lab, glow blue at night. Both are bioluminescent because a chemical they carry, called Luciferin, reacts with a protein called Luciferase. The Luciferin + Luciferase reaction produces an unstable chemical form that releases energy as light. So why does one glow yellow while the other glows blue?

Here’s a little background information about Luciferin:

From the Wikipedia entry for Luciferin:

“Luciferins are a class of small-molecule substrates that are oxidized in the presence of the enzyme luciferase to produce oxyluciferin and energy in the form of light. It is not known just how many types of luciferins there are, but some of the better-studied compounds are listed below. There are many types of luciferins, yet all share the use of reactive oxygen species to emit light.[2]”

From the Wikipedia entry for Firefly Luciferin:

“Different species of fireflies all use the same luciferin, however the color 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 of the luciferase.[7]”

So never mind that there are different colors of light in fireflies vs. plankton, it appears that even different fireflies give off different colors. How can this be?

Digging a bit more, here is some info from the Scripps Institution of Oceanography article: Voyager: Does bioluminescence occur in just one color or are there different colors?

“The color of bioluminescence is based on the structure of two molecules involved in the chemical reaction that produces the light – luciferin, which is oxidized to release the energy that comes out as light, and luciferase, the protein that helps facilitate the reaction. There are several dozen types of luciferin–luciferase chemical reactions, but only a handful have been fully characterized. Some animals don’t even make their own luciferin but get it from their diet….The structures of luciferin and luciferase can be altered to produce different colors of light to serve as a rainbow of research tools.”

So it appears that the “luciferin/luciferase reaction” doesn’t have just one chemical form. It has many forms, lending itself to giving off different colors of light.  Furthermore, the structures of each of those can be altered to change the color given off. Lastly, pH changes might play a part in what takes place chemically, thus adding another avenue to yield variations in color.  It appears there is a lot not yet known about the chemical pathways of bioluminescence. As we learn more, we’ll share it with you!

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