AskDefine | Define pepsin

Dictionary Definition

pepsin n : an enzyme produced in the stomach that splits proteins into peptones

User Contributed Dictionary

English

Noun

  1. A digestive enzyme that chemically digests, or breaks down, proteins into shorter chains of amino acids.

Extensive Definition

Pepsin is a digestive protease () 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.

Precursor

Pepsin is 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. Hydrochloric acid creates an acidic environment which allows pepsinogen to unfold and cleave itself in an autocatalytic fashion, thereby generating pepsin (the active form). Pepsin cleaves the 44 amino acids from pepsinogen to create more pepsin. Pepsin will digest up to 20% of ingested carbon bonds by cleaving preferentially after the N-terminal 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 functions best in acidic environments and is often found in an acidic environment, particularly those with a pH of 1.5 to 2.
Pepsin is said to have an optimum temperature between 37°C and 42°C in humans.

See also

Other important digestive proteases are the pancreatic enzymes trypsin and chymotrypsin. Pepsin denatures if the pH is more than 5.0. Pepsin is potently inhibited by the peptide inhibitor pepstatin.

Storage

Pepsins should be stored at very cold temperatures (between −20°C and −80°C) to prevent autolysis (self-cleavage). Autolysis may also be prevented by storage of pepsins at pH 11 or by using pepsins modified by e.g. reductive methylation. When the pH is adjusted back to pH 6 activity returns.

References

pepsin in Arabic: بيبسن
pepsin in Czech: Pepsin
pepsin in Welsh: Pepsin
pepsin in Danish: Pepsin
pepsin in German: Pepsin
pepsin in Spanish: Pepsina
pepsin in Esperanto: Pepsino
pepsin in French: Pepsine
pepsin in Korean: 펩신
pepsin in Italian: Pepsina
pepsin in Hebrew: פפסין
pepsin in Dutch: Pepsine
pepsin in Japanese: ペプシン
pepsin in Norwegian: Pepsin
pepsin in Occitan (post 1500): Pepsina
pepsin in Polish: Pepsyna
pepsin in Portuguese: Pepsina
pepsin in Russian: Пепсин
pepsin in Simple English: Pepsin
pepsin in Finnish: Pepsiini
pepsin in Swedish: Pepsin
pepsin in Thai: เพพซิน
pepsin in Ukrainian: Пепсин
pepsin in Urdu: پیپسن
pepsin in Chinese: 胃蛋白酶
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