Fireflies and certain other bioluminescent beetles emit light in
their mating rituals. In some North American species, the individual male flashes a
distinctive pattern in flight which is answered by the light from the
female in the nearby trees. The concerted flashing of large groups occurs
in other species. All species utilize the same substrates and similar
luciferases to produce light that ranges from green to red in color.
The ribbon diagram to the left shows the two distinct domains of firefly luciferase. They are connected by a floppy segment of protein that is not shown in the model. It is postulated that the substrates bind and react between these two domains where they are safely protected from water molecules which would otherwise quench the light output.
The reaction substates for light emission can be seen above. Firefly luciferin (yellow), magnesium ions, oxygen, and adenosin triphosphate (orange) are required. The beetle is able to control the light reaction and produce flashing patterns by modulating the flow of oxygen molecules into the light producing organs. Subtle changes in the luciferases of different species cause shifts in the color produced by twisting the luciferin rings relative to each other as it binds to luciferase.