Pepsin
) released by the
chief cells in the
stomach that functions to degrade food
proteins into
peptides.
According to
American Heritage Dictionary, pepsin derives from the
Greek word
pepsis, meaning
digestion (
peptein: to digest).
Pepsin was discovered by
Theodor Schwann in
1836. It was the first animal
enzyme to be discovered.
Pepsin are
expressed as a pro-form
zymogen,
pepsinogen, whose
primary structure has an additional 44
amino acids.
In the stomach,
chief cells release
pepsinogen. This zymogen is activated by
hydrochloric acid (HCl), which is released from
parietal cells in the stomach lining. The hormone
gastrin and the
vagus nerve trigger the release of both
pepsinogen and HCl from the stomach lining when food is ingested. HCl creates an acidic environment which allows pepsinogen to unfold and cleave itself in an
autocatalytic fashion, thereby generating pepsin (the active form). Pepsin will digest up to 20% of ingested proteins by cleaving preferentially at carboxylic groups of aromatic amino acids such as
phenylalanine and
tyrosine. It will not cleave at bonds containing
valine,
alanine or
glycine. Peptides may be further digested by other proteases (in the
duodenum) and eventually absorbed by the body.
Pepsin is stored as pepsinogen so it will only be released when needed, and does not digest the body's own proteins in the stomach's lining.
Pepsin was also originally used in the Pepsi Cola recipe, giving it its name.
Other important digestive proteases are the pancreatic enzymes
trypsin and
chymotrypsin.
*
Pepsin product information from China GreatVista Chemicals*
Pepsin A description from BRENDA database*Gustaitis, Joseph:
Chewing Gum: A Quirky Trait of American Life, American History.
