Luciferase catalyzes light-producing, or chemiluminescent, reactions in which a substrate, luciferin, is oxidized and gives off energy in the form of photons. Many organisms, including bacteria and coelenterates, are bioluminescent, but the one most commonly used in biological applications is the firefly, Photinus pyralis. The oxidation of firefly D-luciferin uses the energy from ATP conversion to AMP and PPi to form oxyluciferin, carbon dioxide, and light. The luciferase system can thus be used to stoichiometrically measure ATP production or use. Luciferase is integral to pyrosequencing, a DNA sequencing protocol used for fragments of less than 400 bases. In a repeating cycle, the pyrophosphate split off when a specific dNTP is polymerized is converted to ATP; that ATP is then measured by light production using luciferase.