Editing Pepsin (section)

== Applications ==
[[File:Beeman's Pepsin Gum DSCF1434.jpg |thumb|right| Beeman's Pepsin Gum]]
[[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 |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
 | 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 | 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 | 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>

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>