Fireflies are a group of insects that possess a lantern organ composed of numerous light-producing cells (photocytes) in their abdomens. The light is produced by a chemical reaction involving the light-emitting organic compound luciferin. In each photocyte, luciferin is activated in an ATP-dependent reaction that is catalyzed by the enzyme luciferase. In the presence of oxygen, the activated luciferin emits light as it is converted to oxyluciferin. The flashes of light are controlled by neurons that innervate the lantern organ. Activated neurons stimulate the release of nitric oxide (NO), an inhibitor of the electron transport chain. Required:
Identify the main source of the ATP used for activating luciferin