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{{Short description|Enzyme}}
{{cs1 config|name-list-style=vanc}}
{{Infobox enzyme
| Name = Pepsin▼
|
| EC_number = 3.4.23.1
| CAS_number = 9001-75-6
| GO_code = 0004194
|
| caption = Pepsin in complex with [[pepstatin]].<ref name="pmid7663352">{{PDB|1PSO}}; {{cite journal | vauthors = Fujinaga M, Chernaia MM, Tarasova NI, Mosimann SC, James MN | title = Crystal structure of human pepsin and its complex with pepstatin | journal = Protein Science | volume = 4 | issue = 5 | pages = 960–72 | date = May 1995 | pmid = 7663352 | pmc = 2143119 | doi = 10.1002/pro.5560040516 }}</ref>▼
▲| caption = Pepsin in complex with [[pepstatin]].<ref name="pmid7663352">{{PDB|1PSO}}; {{cite journal | vauthors = Fujinaga M, Chernaia MM, Tarasova NI, Mosimann SC, James MN | title = Crystal structure of human pepsin and its complex with pepstatin | journal = Protein Science | volume = 4 | issue = 5 | pages = 960–72 | date = May 1995 | pmid = 7663352 | pmc = 2143119 | doi = 10.1002/pro.5560040516 }}</ref>
}}
{{Infobox enzyme
| Name = pepsin B
| EC_number = 3.4.23.2
| CAS_number = 9025-48-3
| GO_code =
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}}
{{Infobox enzyme
| Name = pepsin C (gastricsin)
| EC_number = 3.4.23.3
| CAS_number = 9012-71-9
| GO_code =
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}}
'''Pepsin''' {{IPAc-en|'|p|ɛ|p|s|ɪ|n}} is an [[endopeptidase]] that breaks down [[protein]]s into smaller [[peptide]]s
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
== History ==
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
In 1928, it became one of the first enzymes to be [[protein crystallization|crystallized]] when [[John Howard Northrop|John H. Northrop]] crystallized it using dialysis, filtration, and cooling.<ref name="pmid17758437">{{cite journal | vauthors = Northrop JH | title = Crystalline pepsin | journal = Science | volume = 69 | issue = 1796 | pages = 580 | date = May 1929 | pmid = 17758437 | doi = 10.1126/science.69.1796.580 | bibcode = 1929Sci....69..580N }}</ref>
== Precursor ==
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.
In the stomach, gastric chief cells release pepsinogen. This zymogen is activated by [[hydrochloric acid]] (HCl), which is released from [[parietal cell]]s in the stomach lining. The hormone [[gastrin]] and the [[vagus nerve]] trigger the release of both pepsinogen and HCl from the stomach lining when food is ingested. Hydrochloric acid creates an acidic environment, which allows pepsinogen to unfold and cleave itself in an [[autocatalytic]] fashion, thereby generating pepsin (the active form). Pepsin cleaves the 44 amino acids from pepsinogen to create more pepsin.
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>
== Activity and stability ==
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 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
Pepsin is inactive at pH 6.5 and above, however pepsin is not fully denatured or irreversibly inactivated until pH 8.0.<ref name="Piper_1965" /><ref name="pmid17417109">{{cite journal | vauthors = Johnston N, Dettmar PW, Bishwokarma B, Lively MO, [[Jamie A. Koufman|Koufman JA
Pepsin exhibits a broad cleavage specificity. Pepsin will digest up to 20% of ingested amide bonds.<ref name="Lehninger_5th_ed">{{cite book|last1=Cox|first1=Michael|url=https://archive.org/details/lehningerprincip00lehn_1|title=Lehninger principles of biochemistry|last2=Nelson|first2=David R.|last3=Lehninger|first3=Albert L
▲Pepsin is inactive at pH 6.5 and above, however pepsin is not fully denatured or irreversibly inactivated until pH 8.0.<ref name="Piper_1965" /><ref name="pmid17417109">{{cite journal | vauthors = Johnston N, Dettmar PW, Bishwokarma B, Lively MO, Koufman JA | title = Activity/stability of human pepsin: implications for reflux attributed laryngeal disease | journal = The Laryngoscope | volume = 117 | issue = 6 | pages = 1036–9 | date = June 2007 | pmid = 17417109 | doi = 10.1097/MLG.0b013e31804154c3 | s2cid = 22124366 | url = https://semanticscholar.org/paper/80613cd1fe54316f068eb9bc8b519a8cf803319b }}</ref> Therefore, pepsin in solutions of up to pH 8.0 can be reactivated upon re-acidification. The stability of pepsin at high pH has significant implications on disease attributed to [[laryngopharyngeal reflux]]. Pepsin remains in the larynx following a gastric reflux event.<ref name="pmid15564833">{{cite journal | vauthors = Johnston N, Knight J, Dettmar PW, Lively MO, Koufman J | title = Pepsin and carbonic anhydrase isoenzyme III as diagnostic markers for laryngopharyngeal reflux disease | journal = The Laryngoscope | volume = 114 | issue = 12 | pages = 2129–34 | date = December 2004 | pmid = 15564833 | doi = 10.1097/01.mlg.0000149445.07146.03 | s2cid = 23773155 | url = https://semanticscholar.org/paper/dbe2e27ab7147b5b31b579b9ecfa5f35958c998d }}</ref><ref name="pmid16466100">{{cite journal | vauthors = Johnston N, Dettmar PW, Lively MO, Postma GN, Belafsky PC, Birchall M, Koufman JA | title = Effect of pepsin on laryngeal stress protein (Sep70, Sep53, and Hsp70) response: role in laryngopharyngeal reflux disease | journal = The Annals of Otology, Rhinology, and Laryngology | volume = 115 | issue = 1 | pages = 47–58 | date = January 2006 | pmid = 16466100 | doi = 10.1177/000348940611500108 | s2cid = 29939465 }}</ref> At the mean pH of the laryngopharynx (pH = 6.8) pepsin would be inactive but could be reactivated upon subsequent acid reflux events resulting in damage to local tissues.
▲Pepsin exhibits a broad cleavage specificity. Pepsin will digest up to 20% of ingested amide bonds.<ref name="Lehninger_5th_ed">{{cite book|last1=Cox|first1=Michael|url=https://archive.org/details/lehningerprincip00lehn_1|title=Lehninger principles of biochemistry|last2=Nelson|first2=David R.|last3=Lehninger|first3=Albert L |name-list-style=vanc|publisher=W.H. Freeman|year=2008|isbn=978-0-7167-7108-1|location=San Francisco|url-access=registration |pages = 96}}</ref> Residues in the P1 and P1' positions<ref>The P1 and P1' positions refer to the amino acid residues immediately next to the bond to be cleaved, on the carboxyl and amino side respectively. See {{cite journal | vauthors = Schechter I, Berger A | title = On the active site of proteases. 3. Mapping the active site of papain; specific peptide inhibitors of papain | journal = Biochemical and Biophysical Research Communications | volume = 32 | issue = 5 | pages = 898–902 | date = September 1968 | pmid = 5682314 | doi = 10.1016/0006-291X(68)90326-4 }}</ref> are most important in determining cleavage probability. Generally, hydrophobic amino acids at P1 and P1' positions increase cleavage probability. [[Phenylalanine]], [[leucine]] and [[methionine]] at the P1 position, and [[phenylalanine]], [[tryptophan]] and [[tyrosine]] at the P1' position result in the highest cleavage probability.<ref name="Hamuro_2008" /><ref name="Lehninger_5th_ed" />{{rp|675}} Cleavage is disfavoured by positively charged [[amino acid]]s [[histidine]], [[lysine]] and [[arginine]] at the P1 position.<ref name="Hamuro_2008" />
{{main|Laryngopharyngeal reflux}}
▲== In [[Laryngopharyngeal reflux|laryngopharyngeal]] reflux ==
Pepsin is one of the primary causes of mucosal damage during [[laryngopharyngeal reflux]].<ref name="pmid4884956">{{cite journal | vauthors = Goldberg HI, Dodds WJ, Gee S, Montgomery C, Zboralske FF | title = Role of acid and pepsin in acute experimental esophagitis | journal = Gastroenterology | volume = 56 | issue = 2 | pages = 223–30 | date = February 1969 | pmid = 4884956 | doi = 10.1016/S0016-5085(69)80121-6 | doi-access = free }}</ref><ref name="pmid6808683">{{cite journal | vauthors = Lillemoe KD, Johnson LF, Harmon JW | title = Role of the components of the gastroduodenal contents in experimental acid esophagitis | journal = Surgery | volume = 92 | issue = 2 | pages = 276–84 | date = August 1982 | pmid = 6808683 }}</ref> Pepsin remains in the larynx (pH 6.8) following a gastric reflux event.<ref name="pmid15564833"/><ref name="pmid16466100"/> While enzymatically inactive in this environment, pepsin would remain stable and could be reactivated upon subsequent acid reflux events.<ref name="pmid17417109"/> Exposure of laryngeal mucosa to enzymatically active pepsin, but not irreversibly inactivated pepsin or acid, results in reduced expression of protective proteins and thereby increases laryngeal susceptibility to damage.<ref name="pmid17417109"/><ref name="pmid15564833"/><ref name="pmid16466100"/>
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 =
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
== Inhibitors ==
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
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
A product of protein digestion by pepsin inhibits the reaction.<ref name="Northrop_1932">{{cite journal|vauthors=Northrop HJ|year=1932|title=The story of the isolation of crystalline pepsin and trypsin|journal=[[The Scientific Monthly]]|volume=35|issue=4|pages=333–340|bibcode=1932SciMo..35..333N}}</ref><ref name="pmid4897199">{{cite journal | vauthors = Greenwell P, Knowles JR, Sharp H | title = The inhibition of pepsin-catalysed reactions by products and product analogues. Kinetic evidence for ordered release of products | journal = The Biochemical Journal | volume = 113 | issue = 2 | pages = 363–8 | date = June 1969 | pmid = 4897199 | pmc = 1184643 | doi = 10.1042/bj1130363 }}</ref>
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[[File:Adams Pepsin Tutti Frutti Gum.jpg |thumb|right| Adams Pepsin [[Tutti frutti|Tutti Frutti]] Gum, marketed "For relief of indigestion and dyspepsia"]]
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
| country = US | number = 2259543 | status =patent | title = Fortified Cereal | pubdate = 1938 | inventor = Billings HJ | assign1 = Cream of Wheat Corporation }}</ref> and to prepare animal and vegetable protein hydrolysates for use in flavoring foods and beverages. It is used in the leather industry to remove hair and residual tissue from hides and in the recovery of silver from discarded photographic films by digesting the gelatin layer that holds the silver.<ref name="pmid19872760">{{cite journal | vauthors = Smith ER | title = Gelatinase and the Gates-Gilman-Cowgill Method of Pepsin Estimation | journal = The Journal of General Physiology | volume = 17 | issue = 1 | pages = 35–40 | date = September 1933 | pmid = 19872760 | pmc = 2141270 | doi = 10.1085/jgp.17.1.35 }}</ref> Pepsin was historically an additive of [[Beeman's gum]] brand [[chewing gum]] by Dr. Edwin E. Beeman.
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
Fab and F(ab')2 antibody fragments are used in assay systems where the presence of the Fc region may cause problems. In tissues such as lymph nodes or spleen, or in peripheral blood preparations, cells with Fc receptors (macrophages, monocytes, B lymphocytes, and natural killer cells) are present which can bind the Fc region of intact antibodies, causing background staining in areas that do not contain the target antigen. Use of F(ab')2 or Fab fragments ensures that the antibodies are binding to the antigen and not Fc receptors. These fragments may also be desirable for staining cell preparations in the presence of plasma, because they are not able to bind complement, which could lyse the cells. F(ab')2, and to a greater extent Fab, fragments allow more exact localization of the target antigen, i.e., in staining tissue for electron microscopy. The divalency of the F(ab')2 fragment enables it to cross-link antigens, allowing use for precipitation assays, cellular aggregation via surface antigens, or rosetting assays.<ref name="urlEnzyme Explorer- Pepsin">{{cite web|url=http://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analytical-enzymes/pepsin.html|title=Pepsin|website=Enzyme Explorer|publisher=Merck KGaA}}</ref>
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== External links ==
* 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 }}
* {{MeshName|Pepsin+A}}
* {{MeshName|Pepsinogens}}
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