# Zymogen > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Zymogen > Markdown URL: https://mediated.wiki/source/Zymogen.md > Source: https://en.wikipedia.org/wiki/Zymogen > Source revision: 1356252925 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Inactive precursor to an enzyme In [biochemistry](/source/Biochemistry), a **zymogen** ([/ˈzaɪmədʒən, -moʊ-/](https://en.wikipedia.org/wiki/Help:IPA/English)[1][2]), also called a **proenzyme** ([/ˌproʊˈɛnzaɪm/](https://en.wikipedia.org/wiki/Help:IPA/English)[3][4]), is an inactive [precursor](/source/Protein_precursor) of an [enzyme](/source/Enzyme). A zymogen requires a biochemical change (such as a [hydrolysis](/source/Hydrolysis) reaction revealing the [active site](/source/Active_site), or changing the configuration to reveal the active site) to become an active enzyme. The biochemical change usually occurs in [Golgi bodies](/source/Golgi_apparatus), where a specific part of the precursor enzyme is [cleaved](/source/Post-translational_modification) in order to activate it. The inactivating piece which is cleaved off can be a [peptide](/source/Peptide) unit, or can be independently-folding [domains](/source/Protein_domain) comprising more than 100 [residues](/source/Amino_acid). Although they limit the enzyme's ability, these [N-terminal](/source/N-terminal) extensions of the enzyme or a "prosegment" often aid in the stabilization and [folding](/source/Protein_folding) of the enzyme they inhibit.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] The [pancreas](/source/Pancreas) secretes zymogens partly to prevent the enzymes from digesting proteins in the [cells](/source/Cell_(biology)) where they are synthesised. Enzymes like [pepsin](/source/Pepsin) are created in the form of [pepsinogen](/source/Pepsinogen), an inactive zymogen. Pepsinogen is activated when [chief cells](/source/Gastric_chief_cell) release it into the [gastric acid](/source/Gastric_acid), whose [hydrochloric acid](/source/Hydrochloric_acid) partially activates it.[5] Another partially inactivated pepsinogen completes the activation by removing a peptide, turning the pepsinogen into pepsin. Accidental activation of zymogens can happen when the secretion duct in the pancreas is blocked by a [gallstone](/source/Gallstone), resulting in acute [pancreatitis](/source/Pancreatitis).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] [Fungi](/source/Fungus) also secrete [digestive enzymes](/source/Digestive_enzyme) into the environment as zymogens. The external environment has a different [pH](/source/PH) than inside the fungal cell and this changes the zymogen's structure into an active enzyme.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] Another way that enzymes can exist in inactive forms and later be converted to active forms is by activating only when a [cofactor](/source/Cofactor_(biochemistry)), called a coenzyme, is bound. In this system, the inactive form (the apoenzyme) becomes the active form (the holoenzyme) when the coenzyme binds. In the duodenum, the pancreatic zymogens, trypsinogen, chymotrypsinogen, proelastase and procarboxypeptidase, are converted into active enzymes by enteropeptidase and trypsin. Chymotrypsinogen, a single polypeptide chain of 245 amino acid residues, is converted to alpha-chymotrypsin, which has three polypeptide chains linked by two of the five disulfide bonds present in the primary structure of chymotrypsinogen.[6] ## Examples Examples of zymogens: - [Trypsinogen](/source/Trypsinogen) - [Chymotrypsinogen](/source/Chymotrypsinogen) - [Pepsinogen](/source/Pepsinogen) - Most proteins in the [coagulation system](/source/Coagulation) (examples, prothrombin, or plasminogen) - Some of the proteins of the [complement system](/source/Complement_system) - [Procaspases](/source/Procaspases) - [Pacifastin](/source/Pacifastin) - [Proelastase](https://en.wikipedia.org/w/index.php?title=Proelastase&action=edit&redlink=1) - [Prolipase](https://en.wikipedia.org/w/index.php?title=Prolipase&action=edit&redlink=1) - [Procarboxypolypeptidases](https://en.wikipedia.org/w/index.php?title=Procarboxypolypeptidases&action=edit&redlink=1) ## See also - [Enzyme](/source/Enzyme) - [Protein](/source/Protein) - [Prohormone](/source/Prohormone) ## References 1. **[^](#cite_ref-1)** ["zymogen"](https://www.merriam-webster.com/dictionary/zymogen). *[Merriam-Webster.com Dictionary](/source/Merriam-Webster)*. Merriam-Webster. [OCLC](/source/OCLC_(identifier)) [1032680871](https://search.worldcat.org/oclc/1032680871). Retrieved 2016-01-24. 1. **[^](#cite_ref-2)** ["zymogen"](https://web.archive.org/web/20200322182724/https://www.lexico.com/definition/zymogen). *[Lexico](/source/Lexico) UK English Dictionary*. [Oxford University Press](/source/Oxford_University_Press). Archived from [the original](http://www.lexico.com/definition/zymogen) on 2020-03-22. 1. **[^](#cite_ref-3)** ["proenzyme"](https://www.merriam-webster.com/dictionary/proenzyme). *[Merriam-Webster.com Dictionary](/source/Merriam-Webster)*. Merriam-Webster. [OCLC](/source/OCLC_(identifier)) [1032680871](https://search.worldcat.org/oclc/1032680871). Retrieved 2016-01-24. 1. **[^](#cite_ref-4)** ["proenzyme"](https://web.archive.org/web/20200322185633/https://www.lexico.com/definition/proenzyme). *[Lexico](/source/Lexico) UK English Dictionary*. [Oxford University Press](/source/Oxford_University_Press). Archived from [the original](http://www.lexico.com/definition/proenzyme) on 2020-03-22. 1. **[^](#cite_ref-5)** Dworken HJ (1982-01-01). ["CHAPTER 4 - Functional Characteristics of the Stomach"](https://books.google.com/books?id=KB_FAgAAQBAJ&pg=PA85). *Gastroenterology: Pathophysiology and Clinical Applications*. Butterworth-Heinemann. pp. 85–104. [doi](/source/Doi_(identifier)):[10.1016/b978-0-409-95021-2.50009-1](https://doi.org/10.1016%2Fb978-0-409-95021-2.50009-1). [ISBN](/source/ISBN_(identifier)) [978-0-409-95021-2](https://en.wikipedia.org/wiki/Special:BookSources/978-0-409-95021-2). Retrieved 2020-12-15. 1. **[^](#cite_ref-6)** Mina U, Kumar P (January 2016). ["Life Sciences, Fundamentals and Practice, Part I"](https://www.researchgate.net/publication/310996086). *ResearchGate*. Retrieved 2020-12-15. ## External links Look up ***[zymogen](https://en.wiktionary.org/wiki/Special:Search/zymogen)*** in Wiktionary, the free dictionary. - [Zymogens - Washington.edu](https://courses.washington.edu/conj/bess/zymogens/zymogens.html) - [Molecular mechanisms for the conversion of zymogens to active proteolytic enzymes](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2143990/) --- Adapted from the Wikipedia article [Zymogen](https://en.wikipedia.org/wiki/Zymogen) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Zymogen?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.