"In a firefly bioluminescence reaction, an enzyme known as a luciferase uses adenosine triphosphate (ATP) to activate a molecule called a luciferin. The product of this reaction combines with molecular oxygen to produce an excited-state oxyluciferin species. When oxyluciferin relaxes back to its ground state, energy is released in the form of light…Jellyfish-like animals called ctenophores—can do without [ATP to jump-start bioluminescence]. Instead, they use a luciferin of intrinsically higher energy and prepackage it with oxygen in an enzyme known as a photoprotein. Calcium activates the reaction by changing the shape of the photoprotein, which releases the invested energy in the form of light." (Pepling 2006)
All That Glows: Bioluminescence provides practical applications while still remaining a mystery
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