Pepsin: Difference between revisions

| EC_numberName = 3.4.23.1Pepsin

| GO_codeimage = 00041941PSO.png

| Name = pepsin B

| EC_number = 3.4.23.2

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| imagewidth =

| widthcaption =

| Name = pepsin C (gastricsin)

| EC_number = 3.4.23.3

| GO_codeimage =

| imagewidth =

| widthcaption =

'''Pepsin''' {{IPAc-en|'|p|ɛ|p|s|ɪ|n}} is an [[endopeptidase]] that breaks down [[protein]]s into smaller [[peptide]]s. It is produced in theand [[gastricamino chief cellsacid]]s. of the stomach lining andIt is one of the main [[digestive enzyme]]s in the [[Digestion#Digestive system|digestive systemsystems]]s of humans and many other animals, where it helps [[digestion|digest]] the proteins in [[food]]. Pepsin is an [[aspartic protease]], using a catalytic aspartate in its [[active site]].<ref name="ExPASy" />

It is one of three principal endopeptidases (enzymes cutting proteins in the middle) in the [[human digestive system]], the other two being [[chymotrypsin]] and [[trypsin]]. There are also [[exopeptidase]]s which remove individual amino acids at both ends of proteins ([[carboxypeptidase]]s produced by the pancreas and [[aminopeptidase]]s secreted by the small intestine). During the process of digestion, these enzymes, each of which is specialized in severing links between particular types of [[amino acid]]s, collaborate to break down dietary proteins into their components, i.e., peptides and amino acids, which can be readily [[small intestine#Absorption|absorbed by the small intestine]]. The cleavage specificity of pepsin is broad, but some [[amino acid]]s like [[tyrosine]], [[phenylalanine]] and [[tryptophan]] increase the probability of cleavage.<ref name="Hamuro_2008">{{cite journal | vauthors = Hamuro Y, Coales SJ, Molnar KS, Tuske SJ, Morrow JA | title = Specificity of immobilized porcine pepsin in H/D exchange compatible conditions | journal = Rapid Communications in Mass Spectrometry | volume = 22 | issue = 7 | pages = 1041–6 | date = April 2008 | pmid = 18327892 | doi = 10.1002/rcm.3467 | bibcode = 2008RCMS...22.1041H }}</ref>

Pepsin's [[zymogen|proenzyme]] (proenzyme), '''pepsinogen''', is released by the [[gastric chief cellscell]]s in the stomach wall, and upon mixing with the [[hydrochloric acid]] of the [[gastric acid|gastric juice]], pepsinogen activates to become pepsin.<ref name="ExPASy">{{cite web|url=http://enzyme.expasy.org/EC/3.4.23.1|title=Enzyme entry 3.4.23.1 |website=[[ExPASy]] Bioinformatics Resource Portal|publisher=[[Swiss Institute of Bioinformatics|SIB]]|access-date=14 Dec 2008}}</ref>

Pepsin was one of the first enzymes to be discovered, by [[Theodor Schwann]] in 1836. Schwann coined its name from the [[Ancient Greek|Greek]] word {{lang|grc|πέψις}} ''pepsis'', meaning "[[digestion]]" (from {{lang|grc|πέπτειν}} ''peptein'' "to digest").<ref name="pmid13432398">{{cite journal | vauthors = Florkin M | title = [Discovery of pepsin by Theodor Schwann] | language = fr | journal = Revue Médicale de Liège | volume = 12 | issue = 5 | pages = 139–44 | date = March 1957 | pmid = 13432398 }}</ref><ref name="isbn0-313-22583-4">{{cite book |title=A short history of biology |last=Asimov |first=Isaac | name-list-style = vanc |publisher=Greenwood Press |year=1980 |isbn=9780313225833 |location=Westport, Conn |pages=95 }}</ref><ref>{{Cite web|url=https://www.etymonline.com/word/pepsin|title=Pepsin| vauthors = Harper D |website=[[Online Etymology Dictionary]]}}</ref><ref>{{LSJ|pe/yis|πέψις}}, {{LSJ|pe/ptw|πέπτειν|ref}}.</ref> An acidic substance that was able to convert nitrogen-based foods into water-soluble material was determined to be pepsin.<ref name="pmid12089768">{{cite journal | vauthors = Fruton JS | title = A history of pepsin and related enzymes | journal = The Quarterly Review of Biology | volume = 77 | issue = 2 | pages = 127–47 | date = June 2002 | pmid = 12089768 | doi = 10.1086/340729 | jstor = 3071644 | s2cid = 24979344 }}</ref>

Pepsin is [[gene expression|expressed]] as a [[zymogen]] called '''pepsinogen''', whose [[primary structure]] has an additional 44 [[amino acid]]s compared to the active enzyme.

Pepsinogens are mainly grouped in 5 different groups based on their primary structure: pepsinogen A (also called pepsinogen I), pepsinogen B, progastricsin (also called pepsinogen II and pepsinogen C), prochymosin (also called prorennin) and pepsinogen F (also called pregnancy-associated glycoprotein).<ref>{{cite journal | vauthors = Kageyama T | title = Pepsinogens, progastricsins, and prochymosins: structure, function, evolution, and development | journal = Cellular and Molecular Life Sciences | volume = 59 | issue = 2 | pages = 288–306 | date = February 2002 | pmid = 11915945 | doi = 10.1007/s00018-002-8423-9 | s2cid = 8907522 | pmc = 11146132 }}</ref>

Pepsin is most active in acidic environments between pH 1.5 to 2.5.<ref name="Piper_1965">{{cite journal | vauthors = Piper DW, Fenton BH | title = pH stability and activity curves of pepsin with special reference to their clinical importance | journal = Gut | volume = 6 | issue = 5 | pages = 506–8 | date = October 1965 | pmid = 4158734 | pmc = 1552331 | doi = 10.1136/gut.6.5.506 }}</ref><ref name="urlBRENDA - Information on EC 3.4.23.1 - pepsin A">{{cite web|url=http://www.brenda-enzymes.org/enzyme.php?ecno=3.4.23.1#pH%20OPTIMUM|title=Information on EC 3.4.23.1 - pepsin A|work=[[BRENDA]]-enzymes|access-date=14 Dec 2008}}</ref> Accordingly, its primary site of synthesis and activity is in the stomach ([[pH]] 1.5 to 2). In humans the concentration of pepsin in the stomach reaches 0.5 – 1&nbsp;mg/mL.<ref>{{cite journal | vauthors = Zhu H, Hart CA, Sales D, Roberts NB | title = Bacterial killing in gastric juice--effect of pH and pepsin on Escherichia coli and Helicobacter pylori | journal = Journal of Medical Microbiology | volume = 55 | issue = Pt 9 | pages = 1265–1270 | date = September 2006 | pmid = 16914658 | doi = 10.1099/jmm.0.46611-0 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Brodkorb A, Egger L, Alminger M, Alvito P, Assunção R, Ballance S, Bohn T, Bourlieu-Lacanal C, Boutrou R, Carrière F, Clemente A, Corredig M, Dupont D, Dufour C, Edwards C, Golding M, Karakaya S, Kirkhus B, Le Feunteun S, Lesmes U, Macierzanka A, Mackie AR, Martins C, Marze S, McClements DJ, Ménard O, Minekus M, Portmann R, Santos CN, Souchon I, Singh RP, Vegarud GE, Wickham MS, Weitschies W, Recio I | display-authors = 6 | title = INFOGEST static in vitro simulation of gastrointestinal food digestion | journal = Nature Protocols | volume = 14 | issue = 4 | pages = 991–1014 | date = April 2019 | pmid = 30886367 | doi = 10.1038/s41596-018-0119-1 | doi-access = free | hdl = 11019/1671 | hdl-access = free }}</ref>

Pepsin may also cause mucosal damage during weakly acidic or non-acid gastric reflux. Weak or non-acid reflux is correlated with reflux symptoms and mucosal injury.<ref name="pmid15531244">{{cite journal | vauthors = Tamhankar AP, Peters JH, Portale G, Hsieh CC, Hagen JA, Bremner CG, DeMeester TR | title = Omeprazole does not reduce gastroesophageal reflux: new insights using multichannel intraluminal impedance technology | journal = Journal of Gastrointestinal Surgery | volume = 8 | issue = 7 | pages = 890–7; discussion 897–8 | date = November 2004 | pmid = 15531244 | doi = 10.1016/j.gassur.2004.08.001 | s2cid = 6574429 }}</ref><ref name="pmid15180717">{{cite journal | vauthors = Kawamura O, Aslam M, Rittmann T, Hofmann C, Shaker R | title = Physical and pH properties of gastroesophagopharyngeal refluxate: a 24-hour simultaneous ambulatory impedance and pH monitoring study | journal = The American Journal of Gastroenterology | volume = 99 | issue = 6 | pages = 1000–10 | date = June 2004 | doi = 10.1111/j.1572-0241.2004.30349.x | pmid = 15180717 | s2cid = 8530885 }}</ref><ref>{{cite journal | vauthors = Oelschlager BK, Quiroga E, Isch JA, Cuenca-Abente F | title = Gastroesophageal and pharyngeal reflux detection using impedance and 24-hour pH monitoring in asymptomatic subjects: defining the normal environment | journal = Journal of Gastrointestinal Surgery | volume = 10 | issue = 1 | pages = 54–62 | date = January 2006 | pmid = 16368491 | doi = 10.1016/j.gassur.2005.09.005 | s2cid = 41176354 }}</ref><ref name="pmid16556669">{{cite journal | vauthors = Mainie I, Tutuian R, Shay S, Vela M, Zhang X, Sifrim D, Castell DO | title = Acid and non-acid reflux in patients with persistent symptoms despite acid suppressive therapy: a multicentre study using combined ambulatory impedance-pH monitoring | journal = Gut | volume = 55 | issue = 10 | pages = 1398–402 | date = October 2006 | pmid = 16556669 | pmc = 1856433 | doi = 10.1136/gut.2005.087668 }}</ref> Under non-acid conditions (neutral pH), pepsin is internalized by cells of the upper airways such as the larynx and hypopharynx by a process known as [[receptor-mediated endocytosis]].<ref name="pmid18217514">{{cite journal | vauthors = Johnston N, Wells CW, Blumin JH, Toohill RJ, Merati AL | title = Receptor-mediated uptake of pepsin by laryngeal epithelial cells | journal = The Annals of Otology, Rhinology, and Laryngology | volume = 116 | issue = 12 | pages = 934–8 | date = December 2007 | pmid = 18217514 | doi = 10.1177/000348940711601211 | s2cid = 32026624 }}</ref> The receptor by which pepsin is endocytosed is currently unknown. Upon cellular uptake, pepsin is stored in intracellular vesicles of low pH at which its enzymatic activity would be restored. Pepsin is retained within the cell for up to 24 hours.<ref name="pmid20860281">{{cite journal | vauthors = Johnston N, Wells CW, Samuels TL, Blumin JH | title = Rationale for targeting pepsin in the treatment of reflux disease | journal = The Annals of Otology, Rhinology, and Laryngology | volume = 119 | issue = 8 | pages = 547–58 | date = August 2010 | pmid = 20860281 | doi = 10.1177/000348941011900808 | s2cid = 44531943 }}</ref> Such exposure to pepsin at neutral pH and endocyctosis of pepsin causes changes in gene expression associated with inflammation, which underlies signs and symptoms of reflux,<ref name="pmid19861190">{{cite journal | vauthors = Samuels TL, Johnston N | title = Pepsin as a causal agent of inflammation during nonacidic reflux | journal = Otolaryngology–Head and Neck Surgery | volume = 141 | issue = 5 | pages = 559–63 | date = November 2009 | pmid = 19861190 | doi = 10.1016/j.otohns.2009.08.022 | s2cid = 23855277 }}</ref> and tumor progression.<ref name="pmid11229684">{{cite journal | vauthors = Balkwill F, Mantovani A | title = Inflammation and cancer: back to Virchow? | journal = Lancet | volume = 357 | issue = 9255 | pages = 539–45 | date = February 2001 | pmid = 11229684 | doi = 10.1016/S0140-6736(00)04046-0 | s2cid = 1730949 }}</ref> This and other research<ref name="pmid10722017">{{cite journal | vauthors = Adams J, Heintz P, Gross N, Andersen P, Everts E, Wax M, Cohen J | title = Acid/pepsin promotion of carcinogenesis in the hamster cheek pouch | journal = Archives of Otolaryngology–Head & Neck Surgery | volume = 126 | issue = 3 | pages = 405–9 | date = March 2000 | pmid = 10722017 | doi = 10.1001/archotol.126.3.405 | doi-access = free }}</ref> implicates pepsin in carcinogenesis attributed to gastric reflux.

Pepsin in airway specimens is considered to be a sensitive and specific marker for laryngopharyngeal reflux.<ref name="pmid16094128">{{cite journal | vauthors = Knight J, Lively MO, Johnston N, Dettmar PW, Koufman JA | title = Sensitive pepsin immunoassay for detection of laryngopharyngeal reflux | journal = The Laryngoscope | volume = 115 | issue = 8 | pages = 1473–8 | date = August 2005 | pmid = 16094128 | doi = 10.1097/01.mlg.0000172043.51871.d9 | s2cid = 2196018 | url = https://semanticscholar.org/paper/6a5ff6f5058ca85019b59d31ac47a89fa2037eeb }}</ref><ref name="pmid20392035">{{cite journal | vauthors = Samuels TL, Johnston N | title = Pepsin as a marker of extraesophageal reflux | journal = The Annals of Otology, Rhinology, and Laryngology | volume = 119 | issue = 3 | pages = 203–8 | date = March 2010 | pmid = 20392035 | doi = 10.1177/000348941011900310 | s2cid = 29266257 }}</ref> Research to develop new pepsin-targeted therapeutic and diagnostic tools for gastric reflux is ongoing. A rapid non-invasive pepsin diagnostic called Peptest is now available which determines the presence of pepsin in saliva samples.<ref>{{cite journal | vauthors = Bardhan KD, Strugala V, Dettmar PW | title = Reflux revisited: advancing the role of pepsin | journal = International Journal of Otolaryngology | volume = 2012 | pages = 646901 | year = 2012 | pmid = 22242022 | pmc = 3216344 | doi = 10.1155/2012/646901 | doi-access = free }}</ref>

Pepsin may be inhibited by high pH (see [[#Activity_and_stability|Activity and stability]]) or by inhibitor compounds. [[Pepstatin]] is a low molecular weight compound and potently inhibitor specific for acid proteases with aan inhibitory dissociation constant (Ki) of about 10⁻¹⁰ M for pepsin. The statyl residue of pepstatin is thought to be responsible for pepstatin inhibition of pepsin; [[statine]] is a potential analog of the [[transition state]] for catalysis by pepsin and other acid proteases. Pepstatin does not covalently bind pepsin and inhibition of pepsin by pepstatin is therefore reversible.<ref name="pmid339690">{{cite journalbook | vauthors = Marciniszyn J, Hartsuck JA, Tang J | title = Acid Proteases: Structure, Function, and Biology | chapter = Pepstatin inhibitionInhibition mechanismMechanism | journalseries = Advances in Experimental Medicine and Biology | volume = 95 | pages = 199–210 | year = 1977 | pmid = 339690 | doi = 10.1007/978-1-4757-0719-9_12 | isbn = 978-1-4757-0721-2 }}</ref> 1-bis(diazoacetyl)-2-phenylethane reversibly inactivates pepsin at pH 5, a reaction which is accelerated by the presence of Cu(II).<ref name="pmid4941985">{{cite journal | vauthors = Husain SS, Ferguson JB, Fruton JS | title = Bifunctional inhibitors of pepsin | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 68 | issue = 11 | pages = 2765–8 | date = November 1971 | pmid = 4941985 | pmc = 389520 | doi = 10.1073/pnas.68.11.2765 | bibcode = 1971PNAS...68.2765H | doi-access = free }}</ref>

Porcine pepsin is inhibited by pepsin inhibitor-3 (PI-3) produced by the large roundworm of pig (''[[Ascaris suum]]'').<ref name="Ng_2000">{{cite journal | vauthors = Ng KK, Petersen JF, Cherney MM, Garen C, Zalatoris JJ, Rao-Naik C, Dunn BM, Martzen MR, Peanasky RJ, James MN | display-authors = 6 | title = Structural basis for the inhibition of porcine pepsin by Ascaris pepsin inhibitor-3 | journal = Nature Structural Biology | volume = 7 | issue = 8 | pages = 653–7 | date = August 2000 | pmid = 10932249 | doi = 10.1038/77950 | s2cid = 39440342 }}</ref> PI-3 occupies the active site of pepsin using its N-terminal residues and thereby blocks [[Substrate (chemistry)|substrate]] binding. Amino acid residues 1 - 3 (Gln-Phe-Leu) of mature PI-3 bind to P1' - P3' positions of pepsin. The N-terminus of PI-3 in the PI-3:pepsin complex is positioned by [[hydrogen bond]]s which form an eight-stranded [[Beta sheet|β-sheet]], where three strands are contributed by pepsin and five by PI-3.<ref name="Ng_2000" />

Commercial pepsin is extracted from the glandular layer of hog stomachs. It is a component of [[rennet]] used to curdle milk during the manufacture of cheese. Pepsin is used for a variety of applications in food manufacturing: to modify and provide whipping qualities to soy protein and gelatin,<ref name="isbn981-256-677-5">{{cite book|title=Microbial Biotechnology: Principles And Applications|last1=Kun|first1=Lee Yuan |name-list-style=vanc |publisher=World Scientific Publishing Company|year=2006|isbn=981-256-677-5|edition=2nd|location=Singapore}}</ref> to modify vegetable proteins for use in nondairy snack items, to make precooked cereals into instant hot cereals,<ref name = "US2,259,543">{{ cite patent

Pepsin is commonly used in the preparation of [[F(ab')2 fragment]]s from antibodies. In some assays, it is preferable to use only the antigen-binding (Fab) portion of the [[antibody]]. For these applications, antibodies may be enzymatically digested to produce either an Fab or an F(ab')2 fragment of the antibody. To produce an F(ab')2 fragment, IgG is digested with pepsin, which cleaves the heavy chains near the hinge region.<ref name="pmid27864476">{{cite journal | vauthors = Falkenburg WJ, van Schaardenburg D, Ooijevaar-de Heer P, Tsang-A-Sjoe MW, Bultink IE, Voskuyl AE, Bentlage AE, Vidarsson G, Wolbink G, Rispens T | display-authors = 6 | title = Anti-Hinge Antibodies Recognize IgG Subclass- and Protease-Restricted Neoepitopes | journal = Journal of Immunology | volume = 198 | issue = 1 | pages = 82–93 | date = January 2017 | pmid = 27864476 | doi = 10.4049/jimmunol.1601096 | doi-access = free }}</ref> One or more of the disulfide bonds that join the heavy chains in the hinge region are preserved, so the two Fab regions of the antibody remain joined together, yielding a divalent molecule (containing two antibody binding sites), hence the designation F(ab')2. The light chains remain intact and attached to the heavy chain. The Fc fragment is digested into small peptides. Fab fragments are generated by cleavage of IgG with [[papain]] instead of pepsin. Papain cleaves IgG above the hinge region containing the disulfide bonds that join the heavy chains, but below the site of the disulfide bond between the light chain and heavy chain. This generates two separate monovalent (containing a single antibody binding site) Fab fragments and an intact Fc fragment. The fragments can be purified by gel filtration, ion exchange, or affinity chromatography.<ref name="isbn0-87969-314-2">{{cite book | last1 = Lane | first1 = David Stuart | last2 = Harlow | first2 = Edward |name-list-style=vanc | title = Antibodies: a laboratory manual | publisher = Cold Spring Harbor Laboratory | location = Cold Spring Harbor, N.Y | year = 1988 | pages = A2926 | isbn = 0-87969-314-2 }}</ref>

* The [[MEROPS]] online database for peptidases and their inhibitors: Pepsin A [http://merops.sanger.ac.uk/cgi-bin/merops.cgi?id=A01.001 A01.001] {{Webarchive|url=https://web.archive.org/web/20080320115647/http://merops.sanger.ac.uk/cgi-bin/merops.cgi?id=A01.001 |date=2008-03-20 }}, Pepsin B [http://merops.sanger.ac.uk/cgi-bin/merops.cgi?id=A01.002 A01.002] {{Webarchive|url=https://web.archive.org/web/20071221125051/http://merops.sanger.ac.uk/cgi-bin/merops.cgi?id=A01.002 |date=2007-12-21 }}, Pepsin C (Gastricsin) [http://merops.sanger.ac.uk/cgi-bin/merops.cgi?id=A01.003 A01.003] {{Webarchive|url=https://web.archive.org/web/20200602153344/https://www.ebi.ac.uk/merops/ |date=2020-06-02 }}