Chymotrypsin, Chymotrypsinogen

 Chymotrypsin (E.C. 3.4.21.1) is a mammalian digestive serine proteinase, of the trypsin family, that is synthesized in the acinar cells of the pancreas in the form of an inactive precursor, chymotrypsinogen. This zymogen is stored, along with other digestive enzymes and enzyme precursors, in pancreatic granules, whose contents are released into the duodenum when the pancreas is stimulated by the hormones cholecystokinin and acetylcholine, which are secreted in response to eating a meal.

 Chymotrypsinogen is a single polypeptide chain of 245 amino acid residues that becomes enzymatically active on proteolytic cleavage of the peptide bond that connects Arg15 and Ile16. This cleavage is catalyzed by another pancreatic enzyme, trypsin, which in turn is generated from its zymogen precursor, trypsinogen, by enterokinase, an intestinal serine proteinase. Cleavage of the Arg15 Ile16 bond results in a reorganization of the protein structure, alignment of the catalytic triad, and generation of a substrate binding site (1). Other proteolytic cleavages accompany activation of chymotrypsinogen, but only the one cited is crucial for generating enzymatic activity.

The biological function of chymotrypsin is to digest dietary proteins in the small intestine. It catalyzes the cleavage of peptide bonds in which the carbonyl group is supplied primarily by aromatic or bulky hydrophobic amino acids (tyrosine, tryptophan, phenylalanine, leucine, isoleucine, methionine). These residues become the C-termini of the product peptides and are subsequently removed by digestion with carboxypeptidase A. The catalytic mechanism of chymotrypsin and other serine proteinases is described elsewhere.

 Numerous chymotrypsin-like enzymes generally referred to as chymases have been identified in various animal tissues, particularly in mast cells, neutrophils, and lymphocytes (2). The biological functions of these enzymes are not well understood, but a chymase isolated from human heart is a major angiotensin II -forming enzyme (3). The prostate-specific antigen, which is used in the diagnosis of prostate cancer, is a serine proteinase with limited chymotrypsin-like activity (4).

Being a serine proteinase, chymotrypsin is inhibited by diisopropylfluorophosphate (DIFP) and also by numerous, naturally occurring serine proteinase inhibitors and serpins (5), as well as many small synthetic peptide analogues or active site reagents (6).

References

1. R. M. Stroud, A. A. Kossiakoff, and J. L. Chambers (1977) Annu. Rev. Biophys. Bioeng. 6, 177–193.

2. J. A. Nadel (1991) Ann. N. Y. Acad. Sci. 629, 319–331. 

3. Y. Liao and A. Husain (1995) Can. J. Pharmacol. 11(Suppl. F), 13F–19F. 

4. A. M. el-Shirbiny (1994) Adv. Clin. Chem. 31, 99–133. 

5. J. Potempa, E. Korzus, and J. Travis (1994) J. Biol. Chem. 269, 15957–15960. 

6. J. C. Powers et al. (1989) J. Cell. Biochem. 39, 33–46.

اخر الاخبار

اخبار العتبة العباسية المقدسة

جولة تفقدية لمتابعة خطة تنظيم مداخل المعزّين المشاركين في عزاء ركضة طويريج

لتعزيز التعاون الأكاديمي والبحثي.. جامعة الكفيل توقع اتفاقيتي توأمة مع جامعتين عراقيتين

المجمَع العلميّ يواصل إقامة مجلسه العزائي بذكرى شهادة الإمام الحسين (عليه السلام) في النجف الأشرف

قسم حفظ النظام يواصل تنفيذ خطته لتنظيم سير المواكب والزائرين في شهر المحرم

المزيد

الآخبار الصحية

لهذا السبب.. إغلاق 25 مركزًا لعلاج الإدمان في مصر ؟

خلافا للاعتقاد الشائع.. علماء يكشفون أسرار بذور البطيخ ؟!

هذا ما يحدث لجسمك عند تناولك الطماطم بانتظام !

تعرف على أطعمة تسرّع "تعافي الجسم" من حروق الشمس

المزيد

الآخبار التكنلوجية

الثلوج تغطي الصحراء الأكثر جفافا في العالم!

بتلسكوب "ألما".. التقاط صورا غير مسبوقة لبدايات الكون !

هل هاتفك مراقب؟.. 5 علامات خطيرة تكشف التجسس عليك

دبي تطلق أول رحلة تجريبية للتاكسي الجوي

المزيد

مواضيع ذات صلة

Other Attenuated Systems: Operons, Bacillus subtilis and HIV

Coupling Translation to Termination

trp Multiple Secondary Structures in trp Leader RNA

Early Explorations of the Hypersynthesis

The Serendipitous Discovery of trp Enzyme Hypersynthesis

Rapid Induction Capabilities of the trp Operon

The Aromatic Amino Acid Synthetic Pathway and its Regulation

How AraC Protein Loops and Unloops

DNA Looping and Repression of araBAD

Binding Sites of the ara Regulatory Proteins

Endoplasmic Reticulum-Associated Degradation and the Unfolded Protein Response

Protein Folding and Modifications in the Endoplasmic Reticulum