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Luciferin is the small-molecule substrate that a luciferase enzyme oxidizes to produce light. In the lab the name usually means D-luciferin, the firefly substrate used in bioluminescence reporter assays and animal imaging. Luciferase supplies the catalysis; luciferin is the thing it consumes. This page covers what luciferin is, how the pair works, and what one vendor’s published D-luciferin protocols specify.
General reference information for research use; it is not medical advice and not a validated protocol for your model.
Definition and scope
“Luciferin” is a class name for light-emitting substrates, not a single compound; different organisms use different luciferins. The one most researchers handle is firefly D-luciferin, sold as a free acid or as a potassium salt. One vendor datasheet gives the potassium salt formula as C11H7KN2O3S2, molecular weight 318.41, CAS 115144-35-9 (Selleck Chemicals datasheet S6580, read 2026-11-07).
D-luciferin
D-luciferin is the form firefly luciferase uses as substrate, and reporter-assay and imaging reagents are built around it.
Luciferin and luciferase
The two names are often confused. Luciferase is the enzyme; luciferin is the substrate. For the enzyme-side workflow, see luciferase reporter assay.
How luciferase uses luciferin in practice
Firefly luciferase needs more than luciferin. The in vitro reporter-assay working solution on the Selleck datasheet pairs 1 mM D-luciferin with 3 mM ATP, 1 mM DTT and 15 mM MgSO4 in 25 mM tricine buffer, pH 7.8; 5-10 µL of cell lysate is read with 200 µL of working solution injected and a 10-second integration. ATP and magnesium are therefore reagents in the reaction, which is why ATP-based readouts can use the same chemistry (see ATP assay).
Substrate and modulator
Lembert and Idahl (Biochem J 1995;305:929-933, abstract read 2026-11-07) report that ATP and luciferin are both substrates and modulators of firefly luciferase: high luciferin transiently lowered the reaction rate, recovering over roughly 20 minutes, and albumin reduced the effect. The practical reading is that more substrate is not automatically more signal, so concentration and timing are worth checking rather than assuming.
In vitro versus in vivo preparation: what one vendor protocol states
| Setting | Stated preparation (Selleck datasheet S6580) |
|---|---|
| Cell imaging | 100 mM stock in sterile water; 0.5-1 mM working solution in pre-warmed culture medium; replace medium and incubate 5-10 minutes at 37 °C before imaging. |
| Lysate reporter assay | 1 mM D-luciferin with ATP, DTT and MgSO4 in tricine buffer, injected into lysate in a luminometer. |
| Animal imaging | 15 mg/mL stock in DPBS without Mg2+ and Ca2+, filtered through 0.2 µm; the datasheet states 150 mg/kg intraperitoneally 10-15 minutes before imaging (or 10 µL/g of stock), and adds that a kinetic study should be performed for each animal model to determine peak signal time. |
The kinetic-study note matters most: the 10-15 minute figure is a vendor starting value, and the same datasheet tells users to determine peak time per model. Follow your approved animal protocol and institutional review, not this page.
Storage
The same datasheet advises storing the solution at -20 °C, avoiding freeze-thaw cycles and avoiding light. Use the lot-specific data sheet that ships with your material for the conditions that apply to it.
Where it matters for assay and supply decisions
- Buffer chemistry differs by use. The in vivo stock specifically excludes Mg2+ and Ca2+ (DPBS), while the lysate assay mix adds 15 mM MgSO4. They are different preparations, not interchangeable.
- Light and freeze-thaw are handling variables. The datasheet warns against both, so how a solution is aliquoted and shielded is part of the method.
- Detection side. Luminescence readouts are often compared with other methods; see MTT assay pitfalls and plate readers.
Common misunderstandings
- Luciferin and luciferase are the same thing. They are not: substrate versus enzyme.
- More luciferin always brightens the signal. The 1995 study above found high luciferin transiently reduces the rate.
- One imaging time fits every model. The vendor protocol itself calls for a kinetic study per animal model.
FAQ
Is luciferin toxic to cells?
This page does not state a cytotoxicity figure. Check the supplier’s safety data sheet and include untreated and substrate-only controls in your design.
What are interesting facts about bioluminescence?
One fact from the sources cited here: the firefly reaction needs luciferin, the enzyme, ATP, magnesium and oxygen, and the same chemistry underlies ATP-based assays used in labs.
Where can you find luciferin?
Luciferins occur in bioluminescent organisms such as fireflies, and research-grade D-luciferin is supplied by chemical vendors as a salt or free acid with a data sheet stating handling conditions.
How much luciferin to inject in mice?
One vendor protocol states 150 mg/kg intraperitoneally, from a 15 mg/mL stock, 10-15 minutes before imaging, and says a kinetic study should be done for each animal model. Treat that as a published vendor value for context only; your approved animal protocol governs.
Is luciferin the Bible?
No. Luciferin is a biochemical term for a light-producing substrate, not a scriptural text.
Sources
- Selleck Chemicals, D-Luciferin potassium salt datasheet S6580, selleckchem.com datasheet, read 2026-11-07.
- Lembert N, Idahl LA. Regulatory effects of ATP and luciferin on firefly luciferase activity. Biochem J 1995;305:929-933, PMC1136347, abstract read 2026-11-07.
