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Why does adding ATP restore light to a dimmed firefly-lantern extract?

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time-lapse photo of fireflies — Bioluminescence Time-lapse image of fireflies in the Catskill Mountains, New York. Firefly light is a cold light, with approximately 100 percent of the energy given off as light and only a minute amount as heat. Only light in the visible spectrum is emitted.

Adding adenosine triphosphate (ATP) restores light to a dimmed firefly-lantern extract because ATP is a fundamental component required to initiate the firefly's specific bioluminescent reaction.12

In this process, ATP reacts with firefly luciferase, ionic magnesium, and luciferin to form a high-energy complex known as luciferase-luciferyl-adenylate. When this complex subsequently reacts with molecular oxygen, it releases sufficient energy to shift the complex into an excited electronic state. As the complex returns to its ground state, it radiates a photon of visible light.23

Because the glow of a lantern extract fades as the available ATP is consumed, the addition of fresh ATP provides the necessary fuel to reform the high-energy complex, thereby immediately restoring the light emission. This unique requirement makes the firefly reaction a highly effective assay method for measuring ATP concentrations in biological research.1