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=''Photinus pyralis'' Luciferase=

Purified and characterized in 1978, ''Photinus pyralis'' luciferase (E.C. 1.13.12.7) is an enzyme found within the peroxisomes of the lantern organ located in the abdomen of the North American firefly (''Photinus pyralis'').<ref name=Conti1996>Conti E., Franks N.P., Brick P. (1996) "Crystal structure of firefly luciferase throws light on a superfamily of adenylate-forming enzymes", Structure 4(3): 287-298. doi: 10.1016/S0969-2126(96)00033-0</ref> It is a member of an '''ANL''' superfamily which is made of <big>'''a'''</big>cyl-CoA synthetases, <big>'''n'''</big>on-ribosmal peptide synthetases (NRPSs), and <big>'''l'''</big>uciferases. These enzymes all produce an acyl-AMP intermediate as part of their catalytic reactions.<ref name=Sundlov2012>Sundlov J.A., Fontaine D.M., Southworth T.L., Branchini B.R., and Gulick, A.M. (2012) “Crystal structure of firefly luciferase in a second catalytic conformation supports a domain alternation mechanism”, Biochemistry 51(33): 6493-6495. doi: 10.1021/bi300934s</ref> Luciferases, along with a substrate luciferin, produce light by a reaction with ATP. Organisms that can do this include bacteria, fungi, algae, fish, squid, shrimp, and insects including the firefly.<ref name=Amani2012>Amani-Bayat Z., Hosseinkhani S., Jafari R., and Khajeh K. (2012) “Relationship between stability and flexibility in the most flexible region Photinus pyralis luciferase”, Biochim. Biophy. Acta 1842(2): 350-358. doi 10.1016/j.bbapap.2011.11.003</ref> Some uses of bioluminescence in nature are luring prey, mating and courtship, or helping to camouflage the organism by erasing its shadow or making it invisible from below.<ref name=Shapiro2005>Shapiro E., Lu C., and Baneyx F. (2005) “A Set of Multicolored Photinus Pyralis Luciferase Mutants for in Vivo Bioluminescence Applications”, PEDS 18(12): 581-587. doi:10.1093/protein/gzi066.</ref> ''Photinus pyralis'' luciferase is used in a variety of analytic biological tests as well.

== Structure ==

''Photinus pyralis'' luciferase is a monomeric enzyme composed of 550 residues, resulting in a 62 kDa molecular weight. The protein is divided into two <scene name='69/691535/Colored_domains/2'>domains</scene> (the N-terminal domain and the C-terminal domain) by a wide cleft. Although not shown in the model, the domains are connected by a flexible loop structure. The N-terminal domain (residues 4-436) is much larger than the C-terminal domain (residues 440-544) and is formed by an antiparallel β-barrel (green), as well as two β-sheet subdomains (pink and blue) that create a five-layered αβαβα tertiary structure.<ref name=Conti1996 /> The C-terminal domain, on the other hand, is folded into an α+β tertiary structure (yellow).<ref name=Conti1996 /> Currently, it is thought that the active site is located at the surfaces where the domains meet and that a conformation change occurs after the substrates are bound in which the domains come together and enclose the substrates.<ref name=Conti1996 /><ref name=Marques2009>Marques S.M. and Esteves da Silva J.C.G. (2009) "Firefly bioluminescence: mechanistic approach of luciferase catalyzed reactions", IUBMB Life 61(1): 6-17. doi: 10.1002/iub.134</ref> This enclosement creates a hydrophobic environment which prevents light production from being quenched by water.<ref name=Conti1996 /><ref name=Bedford2012>Bedford R., LePage D., Hoffman R., Kennedy S., Gutschenritter T., Bull L., Sujijantarat N., DiCesare J.C., and Sheaff R.J. (2012) "Luciferase inhibition by a novel naphthoquinone", J. Photochem. Photobiol., B 107: 55-64. doi: 10.1016/j.jphotobiol.2011.11.008</ref>