Luciferase

Luciferase is a generic name for enzymes commonly used in nature for bioluminescence. The name itself is derived from Lucifer, which means light-bearer. The most famous one is firefly luciferase from the firefly Photinus pyralis. In luminescent reactions, light is produced by the oxidation of a luciferin (a pigment), sometimes involving Adenosine triphosphate (ATP). The rates of this reaction between luciferin and oxygen are extremely slow until they are catalyzed by luciferase, often mediated by the presence of calcium ions (an analog of muscle contraction). The reaction takes place in two steps:

luciferin + ATP &rarr; luciferyl adenylate + PPi

luciferyl adenylate + O2 &rarr; oxyluciferin + AMP + light

The reaction is very energy efficient: nearly all of the energy input into the reaction is transformed into light. As a comparison, the incandescent light bulb loses about 90% of its energy to heat.

Luciferin and luciferase are not specific molecules. They are generic terms for a substrate and its associated enzyme (or protein) that catalyze a light-producing reaction. A variety of organisms regulate their light production using different luciferases in a variety of light-emitting reactions. The most famous are the fireflies, although the enzyme exists in organisms as different as the Jack-O-Lantern mushroom (Omphalotus olearius) and many marine creatures. In fireflies, the oxygen required is supplied through a tube in the abdomen called the abdominal trachea. Some organisms, notably certain click beetles, have several different luciferase enzymes, which each can produce different colors from the same luciferin. The luciferases of fireflies - of which there are over 2000 species - and of the Elateroidea (fireflies, click beetles and relatives) in general - are diverse enough to be useful in molecular phylogeny. The most thoroughly studied luciferase is that of the Photinini firefly Photinus pyralis.

Applications
Luciferase can be produced in the lab through genetic engineering for a number of purposes. Luciferase genes can be synthesized and inserted into organisms or transfected into cells. Mice, silkworms, and potatoes are just a few organisms that have already been engineered to produce the protein.

Ex-vivo imaging is a very powerful technique for studying cell populations in whole animals. Different types of cells (e.g. bone marrow stem cells, T-cells) can be engineered to express a luciferase allowing their non-invasive visualization inside a live animal using a sensitive CCD camera.

Light is emitted when luciferase is exposed to the appropriate luciferin substrate. Photon emission can be detected by light sensitive apparatus such as a luminometer or modified optical microscopes. This allows observation of biological processes and stages of infection, for example. Luciferase can be used in blood banks to determine if red blood cells are starting to break down. Forensic investigators can use a dilute solution containing the enzyme to uncover traces of blood remaining on surfaces at a crime scene. Laboratories can employ luciferase to emit light in the presence of certain diseases. Luciferase is used as a reporter protein in molecular studies, for example to test the activity of transcription from specific promoters in cells transfected with luciferase, or to detect the level of cellular ATP. Luciferase is a very heat sensitive protein that is used in studies on protein denaturation, testing the protective capacities of heat shock proteins. The opportunities for using luciferase continue to expand.