Luciferase

Luciferase is an enzyme that catalyzes the bioluminescent oxidation of a luciferin substrate, producing light as a byproduct. In nature, luciferases enable various organisms to emit light for signaling, predation, camouflage, or mating. The light-emitting reaction typically requires molecular oxygen and occurs within a specialized active site of the enzyme.

The most studied luciferases come from different bioluminescent systems. Firefly luciferase (from Photinus and related species) uses the substrate D-luciferin and is ATP-dependent; the reaction emits yellow-green light, usually around 560 nm. Renilla and Gaussia luciferases use coelenterazine as substrate and do not require ATP, producing blue-green light around 480 nm. Bacterial luciferase (LuxAB) uses reduced flavin mononucleotide (FMNH2), a long-chain aldehyde, and oxygen, emitting blue-green light; this system can be coded by luxCDABE in host cells to generate light autonomously.

Because luciferases convert chemical energy into photons with high sensitivity, they are widely used as reporter genes in molecular biology. Applications include monitoring gene expression and promoter activity, assessing cell viability, and enabling noninvasive in vivo imaging in small animals after administration of the appropriate substrate. Advances include codon-optimized luciferase variants for mammalian expression and fusion constructs for multiplex assays.

Structure and genetics vary by system. Firefly luciferase is typically a single ~60 kDa enzyme encoded by the luc gene, while bacterial luciferase involves a multi-gene operon. The choice of system depends on spectral properties, substrate availability, and the experimental context.