|PDB structures||RCSB PDB PDBe PDBsum|
|pepsin C (gastricsin)|
|PDB structures||RCSB PDB PDBe PDBsum|
Pepsin is an enzyme whose zymogen (pepsinogen) is released by the chief cells in the stomach and that degrades food proteins into peptides. It was discovered in 1836 by Theodor Schwann who also coined its name from the Greek word πέψις pepsis, meaning "digestion" (from πέπτειν peptein "to digest"). It was the first enzyme to be discovered, and, in 1928, it became one of the first enzymes to be crystallized, by John H. Northrop. Pepsin is a digestive protease, a member of the aspartate protease family.
Pepsin is one of three principal protein-degrading, or proteolytic, enzymes in the digestive system, the other two being chymotrypsin and trypsin. The three enzymes were among the first to be isolated in crystalline form. During the process of digestion, these enzymes, each of which is specialized in severing links between particular types of amino acids, collaborate to break down dietary proteins into their components, i.e., peptides and amino acids, which can be readily absorbed by the intestinal lining. Pepsin is most efficient in cleaving peptide bonds between hydrophobic and preferably aromatic amino acids such as phenylalanine, tryptophan, and tyrosine.
The term "pepsin" was first coined by Theodor Schwann in the early 19th century. Scientists around this time began discovering many biochemical compounds that play a significant role in biological processes and pepsin was one of them. This acidic substance that was able to convert nitrogen based foods into water soluble material was determined to be pepsin.
In the stomach, chief cells release pepsinogen. This zymogen is activated by hydrochloric acid (HCl), which is released from parietal cells 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. Pepsin will digest up to 20% of ingested amide bonds by cleaving preferentially after the N-terminal:96 of aromatic amino acids such as phenylalanine, tryptophan, and tyrosine.:675 Pepsin exhibits preferential cleavage for hydrophobic, preferably aromatic, residues in P1 and P1' positions. Increased susceptibility to hydrolysis occurs if there is a sulfur-containing amino acid close to the peptide bond, which has an aromatic amino acid. Pepsin cleaves Phe1Val, Gln4His, Glu13Ala, Ala14Leu, Leu15Tyr, Tyr16Leu, Gly23Phe, Phe24
Activity and stability
Pepsin is most active in acidic environments between 37 °C and 42 °C. Accordingly, its primary site of synthesis and activity is in the stomach (pH 1.5 to 2). Pepsin exhibits maximal activity at pH 2.0 and is inactive at pH 6.5 and above, however pepsin is not fully denatured or irreversibly inactivated until pH 8.0. Therefore pepsin in solution 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. 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.
In laryngopharyngeal reflux
Pepsin is one of the primary causes of mucosal damage during laryngopharyngeal reflux. Pepsin remains in the larynx (pH 6.8) following a gastric reflux event. While enzymatically inactive in this environment, pepsin would remain stable and could be reactivated upon subsequent acid reflux events. 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.
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. 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. 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. Such exposure to pepsin at neutral pH and endoyctosis of pepsin causes changes in gene expression associated with inflammation, which underlies signs and symptoms of reflux, and tumor progression. This and other research implicates pepsin in carcinogenesis attributed to gastric reflux.
Pepsin in airway specimens is considered to be a sensitive and specific marker for laryngopharyngeal reflux. 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.
Pepsins should be stored at very low temperatures (between −80 °C and −20 °C) to prevent autolysis (self-digestion).
Pepsin may be inhibited by high pH (see "Activity" and "Stability", above) or by inhibitor compounds. Pepstatin is a low molecular weight compound and potent inhibitor specific for acid proteases with a 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. 1-bis(diazoacetyl)-2-penylethane reversibly inactivates pepsin at pH 5, a reaction which is accelerated by the presence of Cu(II).
Sucralfate also inhibits pepsin activity.
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, to modify vegetable proteins for use in nondairy snack items, to make precooked cereals into instant hot cereals, 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. Pepsin was historically an additive of Beemans gum brand chewing gum by Dr. Edward E. Beeman. It also gave name to Pepsi-Cola, originally formulated with pepsin and kola nuts.
Pepsin is commonly used in the preparation of F(ab')2 fragments 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. 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.
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.
The following three genes encode identical human pepsinogen A enyzmes:
A fourth human gene encodes gastricsin also known as pepsinogen C:
- Florkin M (March 1957). "Discovery of pepsin by Theodor Schwann.". Rev Med Liege (in French) 12 (5): 139–44. PMID 13432398.
- Asimov, Isaac (1980). "page 95". A short history of biology. Westport, Conn: Greenwood Press. ISBN 0-313-22583-4.
- Northrop JH (May 1929). "Crystalline pepsin". Science 69 (1796): 580. Bibcode:1929Sci....69..580N. doi:10.1126/science.69.1796.580. PMID 17758437.
- "Enzyme entry 220.127.116.11". Retrieved 2008-12-14.
- Dunn BM (November 2001). "Overview of pepsin-like aspartic peptidases". Curr Protoc Protein Sci. Chapter 21: Unit 21.3. doi:10.1002/0471140864.ps2103s25. ISBN 0471140864. PMID 18429164.
- Fruton JS (June 2002). "A history of pepsin and related enzymes". Q Rev Biol 77 (2): 127–47. doi:10.1086/340729. JSTOR 3071644. PMID 12089768.
- Cox, Michael; Nelson, David R.; Lehninger, Albert L (2008). Lehninger principles of biochemistry. San Francisco: W.H. Freeman. ISBN 0-7167-7108-X.
- "Effects of pH". Retrieved 2010-04-29.
- "Brenda-enzymes: Entry of pepsin A (EC-Number 18.104.22.168 )". Retrieved 2008-12-14
- Johnston N, Dettmar PW, Bishwokarma B, Lively MO, Koufman JA (June 2007). "Activity/stability of human pepsin: implications for reflux attributed laryngeal disease". Laryngoscope 117 (6): 1036–9. doi:10.1097/MLG.0b013e31804154c3. PMID 17417109.
- Johnston N, Knight J, Dettmar PW, Lively MO, Koufman J (December 2004). "Pepsin and carbonic anhydrase isoenzyme III as diagnostic markers for laryngopharyngeal reflux disease". Laryngoscope 114 (12): 2129–34. doi:10.1097/01.mlg.0000149445.07146.03. PMID 15564833.
- Johnston N, Dettmar PW, Lively MO, Postma GN, Belafsky PC, Birchall M, Koufman JA (January 2006). "Effect of pepsin on laryngeal stress protein (Sep70, Sep53, and Hsp70) response: role in laryngopharyngeal reflux disease". Ann. Otol. Rhinol. Laryngol. 115 (1): 47–58. PMID 16466100.
- Goldberg HI, Dodds WJ, Gee S, Montgomery C, Zboralske FF (February 1969). "Role of acid and pepsin in acute experimental esophagitis". Gastroenterology 56 (2): 223–30. PMID 4884956.
- Lillemoe KD, Johnson LF, Harmon JW (August 1982). "Role of the components of the gastroduodenal contents in experimental acid esophagitis". Surgery 92 (2): 276–84. PMID 6808683.
- Tamhankar AP, Peters JH, Portale G, Hsieh CC, Hagen JA, Bremner CG, DeMeester TR (November 2004). "Omeprazole does not reduce gastroesophageal reflux: new insights using multichannel intraluminal impedance technology". J. Gastrointest. Surg. 8 (7): 890–7; discussion 897–8. doi:10.1016/j.gassur.2004.08.001. PMID 15531244.
- Kawamura O, Aslam M, Rittmann T, Hofmann C, Shaker R (June 2004). "Physical and pH properties of gastroesophagopharyngeal refluxate: a 24-hour simultaneous ambulatory impedance and pH monitoring study". Am. J. Gastroenterol. 99 (6): 1000–10. doi:10.1111/j.1572-0241.2004.30349.x. PMID 15180717.
- Oelschlager BK, Quiroga E, Isch JA, et al. Gastroesophageal and pharyngeal reflux detection using impedance and 24-hour pH monitoring in asymptomatic subjects: defining the normal environment. J Gastrointest Surg 2006;10:54–62.
- Mainie I, Tutuian R, Shay S, Vela M, Zhang X, Sifrim D, Castell DO (October 2006). "Acid and non-acid reflux in patients with persistent symptoms despite acid suppressive therapy: a multicentre study using combined ambulatory impedance-pH monitoring". Gut 55 (10): 1398–402. doi:10.1136/gut.2005.087668. PMC 1856433. PMID 16556669.
- Johnston N, Wells CW, Blumin JH, Toohill RJ, Merati AL (December 2007). "Receptor-mediated uptake of pepsin by laryngeal epithelial cells". Ann. Otol. Rhinol. Laryngol. 116 (12): 934–8. PMID 18217514.
- Johnston N, Wells CW, Samuels TL, Blumin JH (August 2010). "Rationale for targeting pepsin in the treatment of reflux disease". Ann. Otol. Rhinol. Laryngol. 119 (8): 547–58. PMID 20860281.
- Samuels TL, Johnston N (November 2009). "Pepsin as a causal agent of inflammation during nonacidic reflux". Otolaryngol Head Neck Surg 141 (5): 559–63. doi:10.1016/j.otohns.2009.08.022. PMID 19861190.
- Balkwill F, Mantovani A (February 2001). "Inflammation and cancer: back to Virchow?". Lancet 357 (9255): 539–45. doi:10.1016/S0140-6736(00)04046-0. PMID 11229684.
- Adams J, Heintz P, Gross N, Andersen P, Everts E, Wax M, Cohen J (March 2000). "Acid/pepsin promotion of carcinogenesis in the hamster cheek pouch". Arch. Otolaryngol. Head Neck Surg. 126 (3): 405–9. doi:10.1001/archotol.126.3.405. PMID 10722017.
- Knight J, Lively MO, Johnston N, Dettmar PW, Koufman JA (August 2005). "Sensitive pepsin immunoassay for detection of laryngopharyngeal reflux". Laryngoscope 115 (8): 1473–8. doi:10.1097/01.mlg.0000172043.51871.d9. PMID 16094128.
- Samuels TL, Johnston N (March 2010). "Pepsin as a marker of extraesophageal reflux". Ann. Otol. Rhinol. Laryngol. 119 (3): 203–8. PMID 20392035.
- Bardhan, Karna Dev; Strugala, Vicki. Dettmar, Peter (2012). "Reflux Revisited: Advancing the Role of Pepsin". International Journal of Otolaryngology 2012: 1. doi:10.1155/2012/646901. PMC 3216344. PMID 22242022. Retrieved 5 March 2014.
- Marciniszyn J, Hartsuck JA, Tang J (1977). "Pepstatin inhibition mechanism". Adv. Exp. Med. Biol. 95: 199–210. doi:10.1007/978-1-4757-0719-9_12. PMID 339690.
- Husain SS, Ferguson JB, Fruton JS; Ferguson; Fruton (November 1971). "Bifunctional inhibitors of pepsin". Proc. Natl. Acad. Sci. U.S.A. 68 (11): 2765–8. Bibcode:1971PNAS...68.2765H. doi:10.1073/pnas.68.11.2765. PMC 389520. PMID 4941985.
- Northrop HJ (1932). "The story of the isolation of crystalline pepsin and trypsin". The Scientific Monthly 35 (4): 333–340. Bibcode:1932SciMo..35..333N.
- Greenwell P, Knowles JR, Sharp H (June 1969). "The inhibition of pepsin-catalysed reactions by products and product analogues. Kinetic evidence for ordered release of products". Biochem. J. 113 (2): 363–8. PMC 1184643. PMID 4897199.
- Lee Yuan Kun (2006). Microbial Biotechnology: Principles And Applications. World Scientific Publishing Company. ISBN 981-256-677-5.
- US patent 2259543, Billings HJ, "Fortified Cereal", published 1938, assigned to Cream of Wheat Corporation
- Smith ER (September 1933). "Gelatinase and the gates-gilman-cowgill method of pepsin estimation". J. Gen. Physiol. 17 (1): 35–40. doi:10.1085/jgp.17.1.35. PMC 2141270. PMID 19872760.
- Lane, David Stuart; Harlow, Edward; Harlow, Ed (1988). Antibodies: a laboratory manual. Cold Spring Harbor, N.Y: Cold Spring Harbor Laboratory. pp. A2926. ISBN 0-87969-314-2.
- "Enzyme Explorer- Pepsin". Sigma-Aldrich.
- The MEROPS online database for peptidases and their inhibitors: Pepsin A A01.001, Pepsin B A01.002, Pepsin C (Gastricsin) A01.003
- Pepsin A at the US National Library of Medicine Medical Subject Headings (MeSH)
- Pepsinogens at the US National Library of Medicine Medical Subject Headings (MeSH)
- Pepsinogen A at the US National Library of Medicine Medical Subject Headings (MeSH)
- Pepsinogen C at the US National Library of Medicine Medical Subject Headings (MeSH)
- Beemans Gum
- Pepsin: Molecule of the Month, by David Goodsell, RCSB Protein Data Bank