In enzymology, an Oplophorus-luciferin 2-monooxygenase (), also known as Oplophorus luciferase (referred in this article as OpLuc) is a luciferase, an enzyme, from the deep-sea shrimp Oplophorus gracilirostris [2], belonging to a group of coelenterazine luciferases. Unlike other luciferases, it has a broader substrate specificity [3,4,6] and can also bind to bisdeoxycoelenterazine efficiently [3,4]. It is the third example of a luciferase (Other than Aequorea and Renilla) to be purified in lab [2]. The systematic name of this enzyme class is Oplophorus-luciferin:oxygen 2-oxidoreductase (decarboxylating). This enzyme is also called Oplophorus luciferase. Chemical reaction The two substrates of this enzyme are the luciferin, Coelenterazine and O2 and its 3 products are the oxyluciferin, Coelenteramide, CO2, and light. This enzyme belongs to the family of oxidoreductases, specifically those acting on single donors with O2 as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O with incorporation of one atom of oxygen (internal monooxygenases o internal mixed-function oxidases). Although the enzyme is part of the group of enzymes that act on coelenterazine, such as Renilla and Gaussia luciferases, it does not share base pair sequences with these enzymes [3,4,5,7]. OpLuc catalyzes the ATP independent chemical reaction [3,4,5,6]: coelenterazine (Oplophorus luciferin) + O2 coelenteramide + CO2 + hν The result of this process in some loss in as well as a photon of blue light emitted at ~460 nm [2,3,4]. This reaction has an optimal pH of 9, optimal salt concentration of 0.05-0.1 M, and optimal temperature of ~40 C (making it an unusually heat resistant luciferase) [2], although because O.gracilirostris are deep sea animals living in below 20 C temperatures, luciferase is normally expressed and folded at low temperatures [6]. Biological Function When stimulated in Oplophorus gracilirostris, OpLuc is secreted from the base of legs and antennae of the deep-sea shrimp as a defense mechanism. This mechanism causes O.gracilirostris release a luminous, bright blue luciferase cloud [2]. Enzyme Pathway The small protein subunit of OpLuc, 19kda, has an amino terminal peptide sequence that, when stimulated, signals the enzyme to bind to the coelenterazine, Oplophorus luciferin (the substrate) [3,7]. Shown in figure 1,the enzyme then oxidizes the coelenterazine in a water medium into the luminescent product, coelenteramide, and releases as a byproduct [2,3,7]. Structure OpLuc is a complex of two covalently bonded [3] protein subunits: two molecules of 19 kDa and two