Chymotrypsinogen

Chymotrypsinogen is a proteolytic enzyme^[1] and a precursor (zymogen) of the digestive enzyme chymotrypsin. It is a single polypetide chain consisting of 245 amino acid residues. It is synthesized in the acinar cells of the pancreas and stored inside membrane-bounded granules at the apex of the acinar cell. The cell is then stimulated by either a hormonal signal or a nerve impulse and the contents of the granules spill into a duct leading into the duodenum.^[2]

Activation

Chymotrypsinogen must be inactive until it gets to the digestive tract. This prevents damage to the pancreas or any other organs. It is activated into its active form by another enzyme called trypsin. This 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 π-chymotrypsin molecule held together by a disulfide bond. One of the 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 out two dipeptides, which are, Serine-14–Arginine-15 and Threonine-147–Asparagine-148.^[3] This reaction yields the α-chymotrypsin.^[4]

References

1. Schwert G.W, Proteolytic Enzymes. Annual Review of Biochemistry. [online] 1955, 10.1146/annurev.bi.24.070155.000503 http://www.annualreviews.org/doi/abs/10.1146/annurev.bi.24.070155.000503?journalCode=biochem (accessed Oct 10, 2012)
2. Berg.M.J.,Tymoczko.L.J.,Stryer.L., Gatto Jr. J.G. Biochemistry, 7th Ed.; Freeman: New York, 2012.
3. Garret, Reginald (2013). Biochemistry. Canada: Mary Finch. p. 484. ISBN 978-1-133-10629-6.
4. Dryer.J.W.,Neurath.H. The Activation of Chemotrypsinogen: ISOLATION AND IDENTIFICATION OF A PEPTIDE LIBERATED DURING ACTIVATION Department of Biochemistry, University of Washington [1955]http://www.jbc.org/content/217/2/527.full.pdf [accessed Oct. 10, 2012]