Luminescent bacteria are a diverse group, distributed throughout marine, freshwater, and terrestrial environments. They are often symbionts, living in luminous organs of marine fish or soil nematodes.
To the left is the luciferase from the bacterium Vibrio harveyi. This ribbon cartoon shows two discrete subunits having similar structure, although they are not completely identical. They are each colored along their amino acid chains from red to blue. Each is composed of a beta-barrel surrounded by a scaffold of alpha helices. You can identify a 2-fold symmetry along the vertical axis (Hit F5 to refresh) at the 4-helix bundle, colored yellow and orange.
All luminescent bacteria catalyze the same reaction:
An aldehyde (green), reduced flavin mononucleotide (FMNH2)(aqua), and oxygen (yellow) are required for the reaction to occur. First the FMNH2 binds to one of the subunits. The complex then reacts with the aldehyde, producing blue-green light. Only one of the luciferase subunits binds substrates. However, the other subunit is required for efficient luminescence.