Saponin
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Saponins are glycosides of steroids, steroid alkaloids (steroids with a nitrogen function) or triterpenes found in plants, especially in the plant skins where they form a waxy protective coating. They dissolve in water to form a soapy froth. Saponins are believed to be useful in the human diet for controlling cholesterol, but some (including those produced by the soapberry) are poisonous if swallowed and can cause urticaria (skin rash) in many people. Any markedly toxic saponin is known as a sapotoxin.
Saponins have been identified in:
- Soapberry and many other members of the family Sapindaceae, including buckeyes
- Soapwort
- Conkers/horse chestnuts
- Digitalis (as digitonin)
- Grape skin[link]
- Gotu Kola
- Olives
- Panax (as ginsenoside)
- Jiaogulan
- Quillaja saponaria (member of the Rosaceae family)
- Rambutan
- Soybeans
- Yucca
- Aloe
- Quinoa
- Bacopa monnieri
- Chlorophytum species
- Chlorogalum species, soap plants
- Tuberous cucurbit species
- Echinodermata
Saponin is also a mild detergent that can be applied to laboratory studies. When used at 0.04%-0.2% it is sufficient to permeabilize ("make holes in") the plasma membrane as well as the membranes of internal organelles such as ER and Golgi but does not penetrate the nuclear membrane. Therefore it is used in intracellular histochemistry staining to allow antibody access to intracellular proteins.
Because of its reversible nature on cells and its ability to permeabilize cells without destroying cell morphology,it is used in laboratory applications to treat live cells in order to facilitate peptide or reagents such as antibodies to enter cells instead of the harsher detergent triton X-100. It is also done on whole cell preparations such as cell smears and cytospins where the cell membrane is intact. It can also be done on frozen sections but is not used on fixed tissue sections. To preserve the permeabilizing effect, saponin has to be used in all processes involved in the staining steps or otherwise removed after reagent of interest has reached the cell.
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