pepsinogen 3, group I (pepsinogen A) Pepsin in complex with pepstatin.[1] Identifiers Symbol PGA3 Entrez 643834 HUGO 8885 OMIM 169710 RefSeq NM_001079807 UniProt P00790 Other data EC number 3.4.23.1 Locus Chr. 11 q13

pepsinogen 4, group I (pepsinogen A) Identifiers Symbol PGA4 Entrez 643847 HUGO 8886 OMIM 169720 RefSeq NM_001079808 UniProt P00790 Other data EC number 3.4.23.1 Locus Chr. 11 q13

pepsinogen 5, group I (pepsinogen A) Identifiers Symbol PGA5 Entrez 5222 HUGO 8887 OMIM 169730 RefSeq NM_014224 UniProt P00790 Other data EC number 3.4.23.1 Locus Chr. 11 q13

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]

Contents 1 Precursor 2 Storage 3 See also 4 References 5 External links

[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. Pepsin is used for digestion of proteins.

[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

• Chymotrypsin
• Trypsin

[edit] References

[edit] External links

• MeSH Pepsin+A
• MeSH Pepsinogens
• MeSH Pepsinogen+A
• MeSH Pepsinogen+C

v • d • e Digestive system, physiology: gastrointestinal physiology GI tract Upper GI Exocrine Chief cells (Pepsinogen) · Parietal cells (Gastric acid, Intrinsic factor) · Goblet cells (Mucus) Processes Swallowing · Vomiting Fluids Saliva · Gastric juice Lower GI Enteric nervous system Meissner's plexus · Auerbach's plexus Endocrine/paracrine G cells (gastrin) · D cells (somatostatin) · ECL cells (Histamine) enterogastrone: I cells (CCK) · K cells (GIP) · S cells (secretin) Enteroendocrine cells · Enterochromaffin cell · APUD cell Border Brunner's glands · Paneth cells · Enterocytes Fluids Intestinal juice Processes Segmentation contractions · Migrating motor complex · Borborygmus · Defecation Either/both Processes Peristalsis (Interstitial cell of Cajal) · Gastrocolic reflex · Digestion Accessory Fluids Bile · Pancreatic juice Processes Enterohepatic circulation Abdominopelvic Peritoneal fluid digestive system navs: anat of tract,glands,perit,diaphragm/physio/dev, noncongen/congen/congen of d+w/neoplasia, symptoms+signs/eponymous, proc

v • d • e Proteases: aspartic acid proteases (EC 3.4.23) Vertebrate Pepsin · Chymosin · Renin · Signal peptide peptidase · Beta secretase Pathogenic Plasmepsin · HIV-1 protease Cathepsin D · E