Editing Chymotrypsinogen

{{short description|Inactive precursor of digestive enzyme chymotrypsin}}
[[File:Chymotrypsinogen.jpg|thumb|Chymotrypsinogen]]
'''Chymotrypsinogen''' is an inactive precursor ([[zymogen]]) of [[chymotrypsin]], a [[digestive enzyme]] which breaks proteins down into smaller peptides. Chymotrypsinogen is a single [[polypeptide]] chain consisting of 245 [[amino acid]] residues.<ref name="Campbell 2011">{{cite book |last1=Campbell |first1=Mary K. |last2=Farrell |first2=Shawn O. |title=Biochemistry |date=2011 |publisher=Brooks/Cole, Cengage Learning |isbn=9780840068583 |page=176 |edition=7th}}</ref> It is synthesized in the [[acinus|acinar]] cells of the [[pancreas]] and stored inside membrane-bounded granules at the apex of the acinar cell. Release of the granules from the cell is stimulated by either a hormonal signal or a nerve impulse, and the granules spill into a duct leading into the [[duodenum]].<ref>Berg.M.J., Tymoczko.L.J., Stryer.L., Gatto Jr. J.G. ''Biochemistry'', 7th Ed.; Freeman: New York, 2012.</ref>

== Activation ==
Chymotrypsinogen must be inactive until it gets to the digestive tract, in order to prevent damage to the pancreas or any other organs. It is activated by another enzyme called [[trypsin]]. The active form is called π-chymotrypsin and is used to create α-chymotrypsin. Trypsin cleaves the peptide bond in chymotrypsinogen between [[arginine]]-15 and [[isoleucine]]-16. This creates two peptides within the π-chymotrypsin molecule, held together by a disulfide bond. One π-chymotrypsin acts on another by breaking a [[leucine]] and [[serine]] peptide bond. The activated π-chymotrypsin reacts with other π-chymotrypsin molecules to cleave and remove two dipeptides: serine-14–arginine-15 and threonine-147–asparagine-148.<ref>{{Cite book|title=Biochemistry|last=Garret|first=Reginald|publisher=Mary Finch|year=2013|isbn=978-1-133-10629-6|location=Canada|pages=484}}</ref>  This reaction produces α-chymotrypsin.<ref>{{cite journal |last1=Dreyer |first1=William J. |last2=Neurath |first2=Hans |title=The activation of chymotrypsinogen; isolation and identification of a peptide liberated during activation. |journal=The Journal of Biological Chemistry |date=December 1955 |volume=217 |issue=2 |pages=527–39 |doi=10.1016/S0021-9258(18)65918-6 |pmid=13271414 |url=http://www.jbc.org/content/217/2/527.full.pdf |doi-access=free }}</ref> The yield of α-chymotrypsin can be affected by inhibitors such as hydrocinnate and also by pH, temperature and calcium chloride.<ref>{{Cite journal|last1=Sturtevant|first1=Julian M.|last2=Beres|first2=Laszlo|date=May 1971|title=Calorimetric studies of the activation of chymotrypsinogen A|journal=Biochemistry|volume=10|issue=11|pages=2120–2126|doi=10.1021/bi00787a025|issn=0006-2960|pmid=5105558}}</ref>

The activation process can be studied using fluorescence probe 2-p-toluidinylnaphthalene-6-sulfonate (TNS). TNS forms covalent bonds with chymotrypsinogen and as the bonds break to form chymotrypsin in the presence of trypsin, the fluorescence increases.<ref>{{Cite journal|last1=McClure|first1=William O.|last2=Edelman|first2=Gerald M.|date=February 1967|title=Fluorescent Probes for Conformational States of Proteins. III. The Activation of Chymotrypsinogen|journal=Biochemistry|volume=6|issue=2|pages=567–572|doi=10.1021/bi00854a026|issn=0006-2960|pmid=6047640}}</ref>

==References==
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[[Category:Enzymes]]
[[Category:Zymogens]]


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