ATP-dependent bioluminescence in the firefly squid, Watasenia scintillans

The Japanese firefly squid, Watasenia scintillans, emits intense flashes of light from three tiny luminous organs that are located at the tip of each of a pair of ventral arms. Light is also produced from hundreds of other minute organs that are scattered over the body. The luminescence is due to an ATP-dependent reaction, with an optimal pH of 8.80. The decay of light intensity follows first-order kinetics and the decay constant is independent of initial ATP concentration. The light emission also requires MgCl(2), a soluble component, and an insoluble component that is membrane bound. Squids represent a major group of organisms unrelated to fireflies in which ATP is required for bioluminescence.