Editing Zymogen

{{short description|Inactive precursor to an enzyme}}

In [[biochemistry]], a '''zymogen''' ({{IPAc-en|ˈ|z|aɪ|m|ə|dʒ|ən|,_|-|m|oʊ|-}}{{refn|{{MerriamWebsterDictionary|access-date=2016-01-24|zymogen}}}}{{refn|{{Cite dictionary |url=http://www.lexico.com/definition/zymogen |archive-url=https://web.archive.org/web/20200322182724/https://www.lexico.com/definition/zymogen |url-status=dead |archive-date=2020-03-22 |title=zymogen |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}} }}), also called a '''proenzyme''' ({{IPAc-en|ˌ|p|r|oʊ|ˈ|ɛ|n|z|aɪ|m}}{{refn|{{MerriamWebsterDictionary|access-date=2016-01-24|proenzyme}}}}{{refn|{{Cite dictionary |url=http://www.lexico.com/definition/proenzyme |archive-url=https://web.archive.org/web/20200322185633/https://www.lexico.com/definition/proenzyme |url-status=dead |archive-date=2020-03-22 |title=proenzyme |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}} }}), is an inactive [[Protein precursor|precursor]] of an [[enzyme]].  A zymogen requires a biochemical change (such as a [[hydrolysis]] reaction revealing the [[active site]], or changing the configuration to reveal the active site) to become an active enzyme. The biochemical change usually occurs in [[Golgi apparatus|Golgi bodies]], where a specific part of the precursor enzyme is [[Post-translational modification|cleaved]] in order to activate it. The inactivating piece which is cleaved off can be a [[peptide]] unit, or can be independently-folding [[Protein domain|domains]] comprising more than 100 [[amino acid|residues]]. Although they limit the enzyme's ability, these [[N-terminal]] extensions of the enzyme or a "prosegment" often aid in the stabilization and [[protein folding|folding]] of the enzyme they inhibit.{{citation needed|date=February 2021}}

The [[pancreas]] secretes zymogens partly to prevent the enzymes from digesting proteins in the [[Cell (biology)|cells]] where they are synthesised. Enzymes like [[pepsin]] are created in the form of [[pepsinogen]], an inactive zymogen. Pepsinogen is activated when [[Gastric chief cell|chief cell]]s release it into the [[gastric acid]], whose [[hydrochloric acid]] partially activates it.<ref>{{cite book | vauthors = Dworken HJ | chapter = CHAPTER 4 - Functional Characteristics of the Stomach|date=1982-01-01| chapter-url=https://books.google.com/books?id=KB_FAgAAQBAJ&pg=PA85 | title =Gastroenterology: Pathophysiology and Clinical Applications |pages=85–104 |publisher=Butterworth-Heinemann|language=en|doi=10.1016/b978-0-409-95021-2.50009-1|isbn=978-0-409-95021-2|access-date=2020-12-15}}</ref> 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]], resulting in acute [[pancreatitis]].{{citation needed|date=February 2021}}

[[Fungus|Fungi]] also secrete [[digestive enzyme]]s into the environment as zymogens. The external environment has a different [[pH]] than inside the fungal cell and this changes the zymogen's structure into an active enzyme.{{citation needed|date=February 2021}}

Another way that enzymes can exist in inactive forms and later be converted to active forms is by activating only when a [[cofactor (biochemistry)|cofactor]], 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.<ref>{{Cite web| vauthors = Mina U, Kumar P |date=January 2016|title=Life Sciences, Fundamentals and Practice, Part I|url=https://www.researchgate.net/publication/310996086|access-date=2020-12-15|website=ResearchGate|language=en}}</ref>

==Examples==
Examples of zymogens: 

* [[Trypsinogen]]
* [[Chymotrypsinogen]]
* [[Pepsinogen]]
* Most proteins in the [[coagulation|coagulation system]] (examples, prothrombin, or plasminogen)
* Some of the proteins of the [[complement system]]
* [[Procaspases]]
* [[Pacifastin]]
* [[Proelastase]]
* [[Prolipase]]
* [[Procarboxypolypeptidases]]

== See also ==
* [[Enzyme]]
* [[Protein]]
* [[Prohormone]]

== References ==
{{Reflist}}

== External links ==
{{wiktionary}}
* [https://courses.washington.edu/conj/bess/zymogens/zymogens.html Zymogens - Washington.edu]
* [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2143990/ Molecular mechanisms for the conversion of zymogens to active proteolytic enzymes] 

[[Category:Enzymes]]
[[Category:Precursor proteins]]
[[Category:Zymogens| ]]