pepsin

1. A digestive enzyme found in gastric juice that catalyzes the breakdown of protein to peptides.
2. A substance containing pepsin, obtained from the stomachs of hogs and calves and used as a digestive aid.

[Greek pepsis, digestion (from peptein, to digest) + -IN.]

A proteolytic enzyme found in the gastric juice of mammals, birds, reptiles, and fish. It is formed from a precursor, pepsinogen, which is found in the stomach mucosa. Pepsinogen is converted to pepsin either by hydrochloric acid, naturally present in the stomach, or by pepsin itself. See also Enzyme.

Pepsin is prepared commercially from the glandular layer of fresh hog stomachs. It is a part of the crude preparation known as rennet, which is used to curdle milk in preparation for cheese manufacture. Pepsin is also used for a variety of other applications in food manufacturing; to modify soy protein and gelatin, thereby providing whipping qualities; to modify vegetable proteins for use in nondairy snack items; to make precooked cereals into instant hot cereals; and to prepare animal and vegetable protein hydrolysates for use in flavoring foods and beverages.

An enzyme in the gastric juice which hydrolyses proteins to give smaller polypeptides, known as peptones; an endopeptidase. Active only at acid pH, 1.5-2.5. Secreted as the inactive precursor pepsinogen, which is activated by acid.

For more information on pepsin, visit Britannica.com.

A proteolytic enzyme that is the principal digestive component of gastric juice. It acts as a catalyst in the chemical breakdown of protein to form a mixture of polypeptides; it is formed from pepsinogen in the presence of acid or, autocatalytically, in the presence of pepsin itself. Pepsin also has milk-clotting action similar to that of rennin and thereby facilitates the digestion of milk protein.

• p. barrier — the gastric mucosal mechanism which prevents rediffusion of hydrochloric acid back into gastric tissues; includes an electrical resistance, mucus, plus bicarbonate ions trapped in the mucus, endogenous prostaglandins.

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

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.

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.

See also

• Trypsin
• Chymotrypsin

References

1. ^ 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. 
2. ^ Florkin M (March 1957). "[Discovery of pepsin by Theodor Schwann.]" (in French). Rev Med Liege 12 (5): 139–44. PMID 13432398. 
3. ^ Asimov, Isaac (1980). "page 95". A short history of biology. Westport, Conn: Greenwood Press. ISBN 0-313-22583-4. 
4. ^ Northrop JH (May 1929). "Crystalline pepsin". Science (journal) 69 (1796): 580. doi:10.1126/science.69.1796.580. PMID 17758437. 
5. ^ "Enzyme entry 3.4.23.1". http://www.expasy.org/cgi-bin/nicezyme.pl?3.4.23.1. Retrieved 2008-12-14. 
6. ^ Cox, Michael; Nelson, David R. (2008). "page 96". Lehninger Principles of Biochemistry (Fifth ed.). San Francisco: W. H. Freeman. ISBN 0-7167-7108-X. 
7. ^ Cox, Michael; Nelson, David R. (2008). "page 675". Lehninger Principles of Biochemistry (Fifth ed.). San Francisco: W. H. Freeman. ISBN 0-7167-7108-X. 
8. ^ "Enzymes Enzymes". http://www.innvista.com/HEALTH/nutrition/diet/enzymes.htm Enzymes. Retrieved 2008-12-14. 
9. ^ "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 2008-12-14. 

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 digestive system navs: anat of tract,glands,perit/layers/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

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Dansk (Danish)
n. - tale, der skal sætte liv i foretagendet

Nederlands (Dutch)
pepsine

Français (French)
n. - pepsine

Deutsch (German)
n. - (Chem.) Pepsin

Ελληνική (Greek)
n. - (βιολ.) πεψίνη

Italiano (Italian)
pepsina

Português (Portuguese)
n. - pepsina (f)

Русский (Russian)
пепсин

Español (Spanish)
n. - pepsina

Svenska (Swedish)
n. - pepsin (kem.)

中文（简体）(Chinese (Simplified))
胃液素

中文（繁體）(Chinese (Traditional))
n. - 胃液素

한국어 (Korean)
n. - 펩신(위액 속에 있는 단백질 분해 효소), 펩신제

日本語 (Japanese)
n. - ペプシン

العربيه (Arabic)
‏(الاسم) ببسين : مادة كيماويه تساعد على الهضم‏

עברית (Hebrew)
n. - ‮אנזים-עיכול, פפסין‬

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