From Wikipedia, the free encyclopedia
Pepsin is an enzyme that is released by the chief cells in the stomach and that degrades food proteins into peptides. Pepsin was discovered in 1836 by Theodor Schwann[2] who also coined this enzyme's name from the Greek word pepsis, meaning digestion (peptein: to digest).[3] It was the first animal enzyme to be discovered, and, in 1929, it became one of the first enzymes to be crystallized, by John H. Northrop.[4] Pepsin is a digestive protease.[5]
[edit] 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[6] of aromatic amino acids such as phenylalanine, tryptophan, and tyrosine.[7] 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.[8] Pepsin denatures if the pH is more than 5.0.
Pepsin is said to have an optimum temperature between 37°C and 42°C in humans.[9]
Pepsin is potently inhibited by the peptide inhibitor pepstatin.
[edit] 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 modified pepsins (e.g., by reductive methylation). When the pH is adjusted back to 6.0 activity returns.
[edit] See also
[edit] References
- ^ PDB 1PSO; Fujinaga M, Chernaia MM, Tarasova NI, Mosimann SC, James MN (May 1995). "Crystal structure of human pepsin and its complex with pepstatin". Protein Sci. 4 (5): 960–72. doi:10.1002/pro.5560040516. PMID 7663352.
- ^ Florkin M (March 1957). "[Discovery of pepsin by Theodor Schwann.]" (in French). Rev Med Liege 12 (5): 139–44. PMID 13432398.
- ^ Asimov, Isaac (1980). "page 95". A short history of biology. Westport, Conn: Greenwood Press. ISBN 0-313-22583-4.
- ^ Northrop JH (May 1929). "Crystalline pepsin". Science (journal) 69 (1796): 580. doi:10.1126/science.69.1796.580. PMID 17758437.
- ^ "Enzyme entry 3.4.23.1". http://www.expasy.org/cgi-bin/nicezyme.pl?3.4.23.1. Retrieved on 2008-12-14.
- ^ Cox, Michael; Nelson, David R. (2008). "page 96". Lehninger Principles of Biochemistry (Fifth ed.). San Francisco: W. H. Freeman. ISBN 0-7167-7108-X.
- ^ Cox, Michael; Nelson, David R. (2008). "page 675". Lehninger Principles of Biochemistry (Fifth ed.). San Francisco: W. H. Freeman. ISBN 0-7167-7108-X.
- ^ "Enzymes Enzymes". http://www.innvista.com/HEALTH/nutrition/diet/enzymes.htm Enzymes. Retrieved on 2008-12-14.
- ^ "BRENDA: Entry of pepsin A (EC-Number 3.4.23.1 )". http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.4.23.1. Retrieved on 2008-12-14.
[edit] External links
