Chymotrypsin (EC 3.4.21.1, chymotrypsins A and B, alpha-chymar ophth, avazyme, chymar, chymotest, enzeon, quimar, quimotrase, alpha-chymar, alpha-chymotrypsin A, alpha-chymotrypsin) is a digestive enzyme component of pancreatic juice acting in the duodenum, where it performs proteolysis, the breakdown of proteins and polypeptides.[2] Chymotrypsin preferentially cleaves peptide amide bonds where the side chain of the amino acid N-terminal to the scissile amide bond (the P1 position) is a large hydrophobicamino acid (tyrosine, tryptophan, and phenylalanine).[3] These amino acids contain an aromatic ring in their side chain that fits into a hydrophobic pocket (the S1 position) of the enzyme. It is activated in the presence of trypsin. The hydrophobic and shape complementarity between the peptide substrate P1 side chain and the enzyme S1 binding cavity accounts for the substrate specificity of this enzyme.[4][5] Chymotrypsin also hydrolyzes other amide bonds in peptides at slower rates, particularly those containing leucine at the P1 position.[6]
Chymotrypsin
Crystallographic structure of Bos taurus chymotrypsinogen[1]
Chymotrypsin is synthesized in the pancreas. Its precursor is chymotrypsinogen. Trypsin activates chymotrypsinogen by cleaving peptidic bonds in positions Arg15 – Ile16 and produces π-chymotrypsin. In turn, aminic group (-NH3+) of the Ile16 residue interacts with the side chain of Asp194, producing the "oxyanion hole" and the hydrophobic "S1 pocket". Moreover, chymotrypsin induces its own activation by cleaving in positions 14–15, 146–147, and 148–149, producing α-chymotrypsin (which is more active and stable than π-chymotrypsin).[7] The resulting molecule is a three-polypeptide molecule interconnected via disulfide bonds.
Mechanism of action and kinetics
This article is missing information about which specific protein this residue numbering is based on (use hatnote). Please expand the article to include this information. Further details may exist on the talk page.(June 2022)
Molecular mechanism of chymotrypsin-catalyzed hydrolysis of peptide bond. One key aspect is the tetrahedral intermediate Tet 1.
In vivo, chymotrypsin is a proteolytic enzyme (serine protease) acting in the digestive systems of many organisms. It facilitates the cleavage of peptide bonds by a hydrolysis reaction, which despite being thermodynamically favorable, occurs extremely slowly in the absence of a catalyst. The main substrates of chymotrypsin are peptide bonds in which the amino acid N-terminal to the bond is a tryptophan, tyrosine, phenylalanine, or leucine. Like many proteases, chymotrypsin also hydrolyses amide bonds in vitro, a virtue that enabled the use of substrate analogs such as N-acetyl-L-phenylalanine p-nitrophenyl amide for enzyme assays.
Chymotrypsin cleaves peptide bonds by attacking the unreactive carbonyl group with a powerful nucleophile, the serine 195 residue located in the active site of the enzyme, which briefly becomes covalently bonded to the substrate, forming an enzyme-substrate intermediate. Along with histidine 57 and aspartic acid 102, this serine residue constitutes the catalytic triad of the active site. These findings rely on inhibition assays and the study of the kinetics of cleavage of the aforementioned substrate, exploiting the fact that the enzyme-substrate intermediate p-nitrophenolate has a yellow colour, enabling measurement of its concentration by measuring light absorbance at 410 nm.
Chymotrypsin catalysis of the hydrolysis of a protein substrate (in red) is performed in two steps. First, the nucleophilicity of Ser-195 is enhanced by general-base catalysis in which the proton of the serine hydroxyl group is transferred to the imidazole moiety of His-57 during its attack on the electron-deficient carbonyl carbon of the protein-substrate main chain (k1 step). This occurs via the concerted action of the three-amino-acid residues in the catalytic triad. The buildup of negative charge on the resultant tetrahedral intermediate is stabilized in the enzyme’s active site’s oxyanion hole, by formation of two hydrogen bonds to adjacent main-chain amide-hydrogens.
The His-57 imidazolium moiety formed in the k1 step is a general acid catalyst for the k-1 reaction. However, evidence for similar general-acid catalysis of the k2 reaction (Tet2)[8] has been controverted;[9] apparently water provides a proton to the amine leaving group.
Breakdown of Tet1 (via k3) generates an acyl enzyme, which is hydrolyzed with His-57 acting as a general base (kH2O) in formation of a tetrahedral intermediate, that breaks down to regenerate the serine hydroxyl moiety, as well as the protein fragment with the newly formed carboxyl terminus.
^PDB: 1CHG; Freer ST, Kraut J, Robertus JD, Wright HT, Xuong NH (April 1970). "Chymotrypsinogen: 2.5-angstrom crystal structure, comparison with alpha-chymotrypsin, and implications for zymogen activation". Biochemistry. 9 (9): 1997–2009. doi:10.1021/bi00811a022. PMID 5442169.
^Wilcox PE (1970). "[5] Chymotrypsinogens—chymotrypsins". Chymotrypsinogens — chymotrypsins. Methods in Enzymology. Vol. 19. pp. 64–108. doi:10.1016/0076-6879(70)19007-0. ISBN978-0-12-181881-4.
^Cotten, Steven W. (2020-01-01), Clarke, William; Marzinke, Mark A. (eds.), "Chapter 33 - Evaluation of exocrine pancreatic function", Contemporary Practice in Clinical Chemistry (Fourth Edition), Academic Press, pp. 573–585, ISBN978-0-12-815499-1, retrieved 2023-03-18
^Appel W (December 1986). "Chymotrypsin: molecular and catalytic properties". Clin. Biochem. 19 (6): 317–22. doi:10.1016/S0009-9120(86)80002-9. PMID 3555886.
^Berger A, Schechter I (February 1970). "Mapping the active site of papain with the aid of peptide substrates and inhibitors". Philos. Trans. R. Soc. Lond. B Biol. Sci. 257 (813): 249–64. Bibcode:1970RSPTB.257..249B. doi:10.1098/rstb.1970.0024. PMID 4399049. S2CID 6877875.
^Cotten, Steven W. (2020-01-01), Clarke, William; Marzinke, Mark A. (eds.), "Chapter 33 - Evaluation of exocrine pancreatic function", Contemporary Practice in Clinical Chemistry (Fourth Edition), Academic Press, pp. 573–585, ISBN978-0-12-815499-1, retrieved 2023-03-18
^Phillips, Jo (2019). Fundamentals of Enzymology. EDTECH. p. 117. ISBN9781839471605.
^Fersht, A.R.; Requena, Y. (1971). "Mechanism of the -Chymotrypsin-Catalyzed Hydrolysis of Amides. pH Dependence of kc and Km". J. Am. Chem. Soc. 93 (25): 7079–87. doi:10.1021/ja00754a066. PMID 5133099.
^Zeeberg, B.; Caswell, M.; Caplow, M. (1973). "Concerning a reported change in rate-determining step in chymotrypsin catalysis". J. Am. Chem. Soc. 95 (8): 2734–5. doi:10.1021/ja00789a081. PMID 4694533.
chymotrypsin, chymotrypsins, alpha, chymar, ophth, avazyme, chymar, chymotest, enzeon, quimar, quimotrase, alpha, chymar, alpha, chymotrypsin, alpha, chymotrypsin, digestive, enzyme, component, pancreatic, juice, acting, duodenum, where, performs, proteolysis,. Chymotrypsin EC 3 4 21 1 chymotrypsins A and B alpha chymar ophth avazyme chymar chymotest enzeon quimar quimotrase alpha chymar alpha chymotrypsin A alpha chymotrypsin is a digestive enzyme component of pancreatic juice acting in the duodenum where it performs proteolysis the breakdown of proteins and polypeptides 2 Chymotrypsin preferentially cleaves peptide amide bonds where the side chain of the amino acid N terminal to the scissile amide bond the P1 position is a large hydrophobic amino acid tyrosine tryptophan and phenylalanine 3 These amino acids contain an aromatic ring in their side chain that fits into a hydrophobic pocket the S1 position of the enzyme It is activated in the presence of trypsin The hydrophobic and shape complementarity between the peptide substrate P1 side chain and the enzyme S1 binding cavity accounts for the substrate specificity of this enzyme 4 5 Chymotrypsin also hydrolyzes other amide bonds in peptides at slower rates particularly those containing leucine at the P1 position 6 ChymotrypsinCrystallographic structure of Bos taurus chymotrypsinogen 1 IdentifiersEC no 3 4 21 1CAS no 9004 07 3DatabasesIntEnzIntEnz viewBRENDABRENDA entryExPASyNiceZyme viewKEGGKEGG entryMetaCycmetabolic pathwayPRIAMprofilePDB structuresRCSB PDB PDBe PDBsumGene OntologyAmiGO QuickGOSearchPMCarticlesPubMedarticlesNCBIproteinsChymotrypsin CIdentifiersEC no 3 4 21 2CAS no 9036 09 3DatabasesIntEnzIntEnz viewBRENDABRENDA entryExPASyNiceZyme viewKEGGKEGG entryMetaCycmetabolic pathwayPRIAMprofilePDB structuresRCSB PDB PDBe PDBsumSearchPMCarticlesPubMedarticlesNCBIproteinsStructurally it is the archetypal structure for its superfamily the PA clan of proteases Contents 1 Activation 2 Mechanism of action and kinetics 3 Isozymes 4 See also 5 References 6 Further reading 7 External linksActivation EditChymotrypsin is synthesized in the pancreas Its precursor is chymotrypsinogen Trypsin activates chymotrypsinogen by cleaving peptidic bonds in positions Arg15 Ile16 and produces p chymotrypsin In turn aminic group NH3 of the Ile16 residue interacts with the side chain of Asp194 producing the oxyanion hole and the hydrophobic S1 pocket Moreover chymotrypsin induces its own activation by cleaving in positions 14 15 146 147 and 148 149 producing a chymotrypsin which is more active and stable than p chymotrypsin 7 The resulting molecule is a three polypeptide molecule interconnected via disulfide bonds Mechanism of action and kinetics EditThis article is missing information about which specific protein this residue numbering is based on use hatnote Please expand the article to include this information Further details may exist on the talk page June 2022 Molecular mechanism of chymotrypsin catalyzed hydrolysis of peptide bond One key aspect is the tetrahedral intermediate Tet 1 See also Catalytic triad In vivo chymotrypsin is a proteolytic enzyme serine protease acting in the digestive systems of many organisms It facilitates the cleavage of peptide bonds by a hydrolysis reaction which despite being thermodynamically favorable occurs extremely slowly in the absence of a catalyst The main substrates of chymotrypsin are peptide bonds in which the amino acid N terminal to the bond is a tryptophan tyrosine phenylalanine or leucine Like many proteases chymotrypsin also hydrolyses amide bonds in vitro a virtue that enabled the use of substrate analogs such as N acetyl L phenylalanine p nitrophenyl amide for enzyme assays Chymotrypsin cleaves peptide bonds by attacking the unreactive carbonyl group with a powerful nucleophile the serine 195 residue located in the active site of the enzyme which briefly becomes covalently bonded to the substrate forming an enzyme substrate intermediate Along with histidine 57 and aspartic acid 102 this serine residue constitutes the catalytic triad of the active site These findings rely on inhibition assays and the study of the kinetics of cleavage of the aforementioned substrate exploiting the fact that the enzyme substrate intermediate p nitrophenolate has a yellow colour enabling measurement of its concentration by measuring light absorbance at 410 nm Chymotrypsin catalysis of the hydrolysis of a protein substrate in red is performed in two steps First the nucleophilicity of Ser 195 is enhanced by general base catalysis in which the proton of the serine hydroxyl group is transferred to the imidazole moiety of His 57 during its attack on the electron deficient carbonyl carbon of the protein substrate main chain k1 step This occurs via the concerted action of the three amino acid residues in the catalytic triad The buildup of negative charge on the resultant tetrahedral intermediate is stabilized in the enzyme s active site s oxyanion hole by formation of two hydrogen bonds to adjacent main chain amide hydrogens The His 57 imidazolium moiety formed in the k1 step is a general acid catalyst for the k 1 reaction However evidence for similar general acid catalysis of the k2 reaction Tet2 8 has been controverted 9 apparently water provides a proton to the amine leaving group Breakdown of Tet1 via k3 generates an acyl enzyme which is hydrolyzed with His 57 acting as a general base kH2O in formation of a tetrahedral intermediate that breaks down to regenerate the serine hydroxyl moiety as well as the protein fragment with the newly formed carboxyl terminus Isozymes EditChymotrypsinogen B1IdentifiersSymbolCTRB1NCBI gene1504HGNC2521OMIM118890RefSeqNM 001906UniProtP17538Other dataEC number3 4 21 1LocusChr 16 q23 1Search forStructuresSwiss modelDomainsInterPro Chymotrypsinogen B2IdentifiersSymbolCTRB2NCBI gene440387HGNC2522RefSeqNM 001025200UniProtQ6GPI1Other dataEC number3 4 21 1LocusChr 16 q22 3Search forStructuresSwiss modelDomainsInterPro Chymotrypsin C caldecrin IdentifiersSymbolCTRCNCBI gene11330HGNC2523OMIM601405RefSeqNM 007272UniProtQ99895Other dataEC number3 4 21 2LocusChr 1 p36 21Search forStructuresSwiss modelDomainsInterProSee also EditTrypsin PA clan of proteasesReferences Edit PDB 1CHG Freer ST Kraut J Robertus JD Wright HT Xuong NH April 1970 Chymotrypsinogen 2 5 angstrom crystal structure comparison with alpha chymotrypsin and implications for zymogen activation Biochemistry 9 9 1997 2009 doi 10 1021 bi00811a022 PMID 5442169 Wilcox PE 1970 5 Chymotrypsinogens chymotrypsins Chymotrypsinogens chymotrypsins Methods in Enzymology Vol 19 pp 64 108 doi 10 1016 0076 6879 70 19007 0 ISBN 978 0 12 181881 4 Cotten Steven W 2020 01 01 Clarke William Marzinke Mark A eds Chapter 33 Evaluation of exocrine pancreatic function Contemporary Practice in Clinical Chemistry Fourth Edition Academic Press pp 573 585 ISBN 978 0 12 815499 1 retrieved 2023 03 18 Appel W December 1986 Chymotrypsin molecular and catalytic properties Clin Biochem 19 6 317 22 doi 10 1016 S0009 9120 86 80002 9 PMID 3555886 Berger A Schechter I February 1970 Mapping the active site of papain with the aid of peptide substrates and inhibitors Philos Trans R Soc Lond B Biol Sci 257 813 249 64 Bibcode 1970RSPTB 257 249B doi 10 1098 rstb 1970 0024 PMID 4399049 S2CID 6877875 Cotten Steven W 2020 01 01 Clarke William Marzinke Mark A eds Chapter 33 Evaluation of exocrine pancreatic function Contemporary Practice in Clinical Chemistry Fourth Edition Academic Press pp 573 585 ISBN 978 0 12 815499 1 retrieved 2023 03 18 Phillips Jo 2019 Fundamentals of Enzymology EDTECH p 117 ISBN 9781839471605 Fersht A R Requena Y 1971 Mechanism of the Chymotrypsin Catalyzed Hydrolysis of Amides pH Dependence of kc and Km J Am Chem Soc 93 25 7079 87 doi 10 1021 ja00754a066 PMID 5133099 Zeeberg B Caswell M Caplow M 1973 Concerning a reported change in rate determining step in chymotrypsin catalysis J Am Chem Soc 95 8 2734 5 doi 10 1021 ja00789a081 PMID 4694533 Further reading EditStryer L Berg JM Tymoczko JL 2002 Biochemistry San Francisco W H Freeman ISBN 0 7167 4684 0 Grisham CM Reginald H 2005 Biochemistry Australia Thomson Brooks Cole ISBN 0 534 49033 6 External links EditThe MEROPS online database for peptidases and their inhibitors S01 001 Chymotrypsin at the U S National Library of Medicine Medical Subject Headings MeSH Portal Biology Retrieved from https en wikipedia org w index php title Chymotrypsin amp oldid 1145357622, wikipedia, wiki, book, books, library,
