digitonin

Digitonin is a natural steroidal saponin obtained from Digitalis species, such as Digitalis purpurea. It is a glycoside of the steroidal sapogenin digitogenin, consisting of a steroid aglycone linked to a branched oligosaccharide. Digitonin is poorly soluble in water but can be dissolved in small amounts of organic solvents and used as concentrated stock solutions in solvents such as DMSO or ethanol.

In biochemistry, digitonin is valued for its ability to selectively permeabilize cell membranes that are rich in cholesterol. It binds cholesterol to form digitonin–cholesterol complexes that disrupt membrane integrity and create pores, allowing cytosolic contents to leak out while preserving more cholesterol-poor organelle membranes at low concentrations. This property makes digitonin useful for releasing cytosolic components, isolating organelles, or accessing intracellular enzymes in a controlled way. The response depends on cholesterol content and cell type, so concentration must be optimized for each preparation.

Typical working concentrations range from a few micrograms per milliliter up to tens of micrograms per milliliter, with common permeabilization protocols employing around 5–20 μg/mL. Digitonin stocks are often prepared in DMSO or ethanol and added to buffers so that the final solvent concentration remains tolerable for the assay.

Safety and handling: Digitonin is a toxic glycoside with potential cardiotonic effects if ingested; appropriate laboratory precautions should be used. Storage is generally at low temperature and protected from light.

History and naming: The compound is named after Digitalis, reflecting its plant origin and long use in membrane biology since the mid-20th century.