Bioluminescence

The two basic components needed to produce a bioluminescent reaction, luciferin and luciferase, can be isolated from the organisms that produce them. When they are mixed in the presence of oxygen and the appropriate cofactors, these components will produce light with an intensity dependent on the quantity of luciferin and luciferase Fireflies have a bioluminescent organ in their abdomen that they use to attract mates. Enzymes within the organ react with oxygen to produce light. The insect controls the flashes by regulating the flow of oxygen. Photograph by Roy Morsch. Stock Market. Reproduced by permission. added as well as the oxygen and cofactor concentrations. Luciferases isolated from fireflies and other beetles are commonly used in research.

Scientists have used isolated luciferin and luciferase to determine the concentrations of important biological molecules such as ATP and calcium. After adding a known amount of luciferin and luciferase to a blood or tissue sample, the cofactor concentrations may be determined from the intensity of the light emitted. Scientists have also found numerous other uses for the bioluminescent reaction such as using it to quantify specific molecules that do not directly participate in the bioluminescence reaction. To do this, scientists attach luciferase to antibodies—molecules produced by the immune system that bind to specific molecules called antigens. The antibody-luciferase complex is added to a sample where it binds to the molecule to be quantified. Following washing to remove unbound antibodies, the molecule of interest can be quantified indirectly by adding luciferin and measuring the light emitted. Methods used to quantify particular compounds in biological samples such as the ones described here are called assays.

Luciferase is often used as a "reporter gene" to study how individual genes are activated to produce protein or repressed to stop producing protein. Most genes are turned on and off by DNA located in front of the part of the gene that codes for protein. This region is called the gene promoter. A specific gene promoter can be attached to the DNA that codes for firefly luciferase and introduced into an organism. The activity of the gene promoter can then be studied by measuring the bioluminescence produced in the luciferase reaction. Thus, the luciferase gene can be used to "report" the activity of a promoter for another gene.

In recent studies, luciferase has been used to study viral and bacterial infections in living animals and to detect bacterial contaminants in food. The luciferase reaction also is used to determine DNA sequences, the order of the four types of molecules that comprise DNA and code for proteins.