Firefly luciferase generates light from luciferin in a multistep process. In the presence of oxygen, luciferase catalyzes the oxidation of an organic molecule called luciferin. In the luciferase reaction, light is emitted when luciferase acts on the appropriate luciferin substrate. The N-terminal domain is conserved between dinoflagellate luciferase and luciferin binding proteins (LBPs). This reaction involves a light-emitting pigment, the luciferin, and a luciferase, the enzyme component. The enzyme catalyses the oxidation of firefly luciferin, requiring oxygen and ATP. A "luciferin" and oxygen is always catalyzed by luciferase to light. This shows that luciferase can differentiate between the isomers of the luciferin structure. Two chemicals, luciferin, and luciferase that react with one another to create a soft glow. When the pH drops, luciferase changes its shape, allowing luciferin, more specifically tetrapyrrole, to bind. In all characterized cases, the enzyme catalyzes the oxidation of the luciferin. Firefly luciferin can be oxidized to produce an excited complex. The in vivo synthesis of firefly luciferin is not completely understood. Other important thiazole derivatives are benzothiazoles, for example, the firefly chemical luciferin. Other substrates include luciferin, thyroid hormones and quinolones.