D-Luciferin is a bioluminescence substrate of luciferase gene reporter systems often used in in vivo imaging.

Isolated from the North American firefly (Photinus pyralis) and other beetle species, luciferase is an enzyme that oxidizes luciferin in an ATP-dependent manner, producing light in the process. This chemiluminescence has a peak wavelength at 560 nm, with the intensity of the light proportional to luciferase activity, and can be monitored using a luminometer or scintillation counter.

Luciferase/luciferin reporter systems are often used to study transcription in transient and stably transformed eukaryotic cells, by inclusion of the Luc gene. Compared to other methods, luminescence is highly sensitive, since there is little to no background, allowing detection of low-level gene expression. This system has also been used to quantify ATP, which has enabled applications ranging from cell viability assays to quality assurance testing in food safety to determine if there is contamination of surfaces. On the flip side, one drawback, compared to colorimetric systems such as HRP and alkaline phosphatase (AP), is that luciferase is less tolerant to chemical modifications.

This D-Luciferin product is provided as a lyophilized powder in monopotassium salt form, with a molecular weight of 318.41 daltons (C11H7N2O3S2•K). It is water soluble and easily dissolvable in an aqueous buffer. It can also pass through cell membranes, allowing for live cell experiments. In such in vivo conditions, it has a Km for luciferase of approximately 1 mM; on the other hand, it has a Km of 10 uM for in vitro conditions (Ignowski et al., 2004). D-Luciferin is also sometimes referred to as Beetle Luciferin or Firefly Luciferin; these are equivalent terms. Aside from potassium salt, D-Luciferin is also available as d-luciferin sodium salt, free acid and many other forms.