Fireflies, also called Lightening Bugs or Glow Worms, are a family of soft-bodied brownish or black beetles with an organ on the tip of their abdomen that blinks with a green or yellow light when activated. There are roughly 2000 types of fireflies, but the beetles capable of luminescence are nocturnal insects that generate light to attract potential mates. Many of their larvae also generate light which is believed to be a warning to predators, since they contain chemicals toxic to their enemies.
Fireflies produce light by means of a chemical reaction in which luciferin is converted to oxyluciferin by an enzyme called luciferase. Luciferins are biological pigments which, when oxidized, release energy in the form of light. Luciferins are also found in some bacteria and marine life. Generation of light from luciferin is a very efficient process (90% efficiency). Different wavelengths of light are generated depending on the type of luciferin. There are many different luciferase enzymes, each specific for a particular luciferin pigment.
The reaction of luciferase with luciferin requires ATP (adenosine triphosphate) for energy and proceeds in two steps:
luciferin + ATP => luciferyl adenylate + PPi
luciferyl adenylate + O2 => oxyluciferin + AMP + light
Calcium is also sometimes required for luciferase activity. The reaction of luciferin with oxygen proceeds very slowly in the absence of enzymatic catalysis.
Luciferase enzymes have been exploited for use in many different areas of biotechnology, most predominantly as bioindicators for gene expression studies. When inserted into cells by gene cloning techniques, they allow detection and monitoring of the cells using imaging equipment. This approach has been used in bioremediation studies for monitoring the distribution and survival of GMOs, and can be used to track and monitor viability of cells in larger organisms, in vivo.
The luciferase enzyme is also used to study promoter and transcriptional activation for other genes. In order to do this, the gene for luciferase is cloned with an upstream promoter for the other gene of interest, and might be expressed in a common bacterial host such as E. coli. When the promoter is activated, the result, in the presence of luciferin, is generation of detectable light.
The luciferase reporter assay has been used to measure transcriptional activity in many areas of biomedical research for the study of diseases such as diabetes, and various cancers. It has also been used to investigate human conditions such as pulmonary responses to allergens and environmental contaminants, and the mechanism and treatment of gastric inflammation. A similar strategy can be used to detect cellular ATP concentrations in situ. Luciferase is very sensitive to heat denaturation and has also been used to study the protective effects of heat shock proteins.
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