-!- The enzyme, which is found in fireflies (Lampyridae), is responsible for their biolouminescence. -!- The reaction begins with the formation of an acid anhydride between the carboxylic group of D-firefly luciferin and AMP, with the release of diphosphate. -!- An oxygenation follows, with release of the AMP group and formation of a very short-lived peroxide that cyclizes into a dioxetanone structure, which collapses, releasing a CO(2) molecule. -!- The spontaneous breakdown of the dioxetanone (rather than the hydrolysis of the adenylate) releases the energy (about 50 kcal/mole) that is necessary to generate the excited state of oxyluciferin. -!- The excited luciferin then emits a photon, returning to its ground state. -!- The enzyme has a secondary acyl-CoA ligase activity when acting on L-firefly luciferin.