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What Makes Fireflies Glow?


On a warm summer night, have you ever wondered how the fireflies you see in your back yard or a nearby woodland make their light?

HWI scientist Andrew Gulick and Connecticut College Professor Bruce Branchini, together with colleagues at Yale University, have recently taken a big step towards answering this question.

The glow of fireflies is an example of bioluminescence or the production and emission of light by a living organism. Bioluminescence occurs widely in marine animals and in some fungi, bacteria, and terrestrial invertebrates such as fireflies.

firefliesFireflies have specialized cells in their abdomens that make light. These cells contain a small molecule called luciferin and an enzyme called luciferase.

Bioluminescence results when luciferase catalyzes the oxidation of luciferin and releases light energy in the process. In fireflies, this chemical reaction requires participation by the high-energy compound, adenosine triphosphate (ATP), and the reaction releases oxyluciferin, adenosine monophosphate (AMP), phosphate ions, and carbon dioxide (CO2) as waste products.

In a recent paper in the Journal of the American Chemical Society, the team presents experimental evidence that a single electron-transfer pathway is involved in the oxidative process. This mechanism may be a common feature of bioluminescent processes in which light is produced by an enzyme in the absence of any additional cofactors. The work follows up on structural studies performed by Gulick and Branchini in 2012 in which the structure of the luciferase enzyme in its active light-producing conformation was determined.

Bioluminescence has several different functions in nature. These include defense, camouflage, luring or confusing prey, and mate attraction or recognition. Male fireflies produce a species-specific light-flashing pattern consisting of one or more flashes followed by a characteristic pause. Female fireflies respond when they recognize a suitable mate.

The study of firefly luciferase, and of bioluminescence in general, is a wonderful example of the pursuit of basic biomedical research and its potential to develop in ways that were not originally conceived. The sensitivity and uniqueness of the pulse of light produced by luciferase has allowed it to be used in a wide range of studies that have probed many important biomedical problems. Because the luciferase reaction also requires energy in the form of ATP, the luciferin-luciferase chemical reaction has been used for years to measure the amount of ATP produced by other reactions. Additionally, researchers have devised luciferase-based detection systems that have been used to understand signaling pathways involved in cellular growth and proliferation.

The Gulick and Branchini labs have been collaborating together on the study of the structure and function of luciferase for nearly 10 years, allowing several students in the Gulick lab the opportunity to study these interesting enzymes. Additionally, Kelsey Taylor, an undergraduate from Connecticut College who worked on this project with Dr. Branchini, came to HWI through the summer internship program a few years ago.

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