Editing Chymosin (section)

==Occurrence==
Chymosin is found in a wide range of [[tetrapods]],<ref name=lineage/> although it is best known to be produced by [[ruminant]] animals in the lining of the [[abomasum]]. Chymosin is produced by [[gastric chief cell]]s in newborn mammals<ref name="pmid11534329">{{cite journal | vauthors = Kitamura N, Tanimoto A, Hondo E, Andrén A, Cottrell DF, Sasaki M, Yamada J | title = Immunohistochemical study of the ontogeny of prochymosin--and pepsinogen-producing cells in the abomasum of sheep | journal = Anatomia, Histologia, Embryologia | volume = 30 | issue = 4 | pages = 231–5 | date = August 2001 | pmid = 11534329 | doi = 10.1046/j.1439-0264.2001.00326.x | s2cid = 7552821 }}</ref> to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption. Non-ruminant species that produce chymosin include pigs, cats, seals,<ref name= OMIM>Staff,  Online Mendelian Inheritance in Man (OMIM) Database.  Last updated February 21, 1997 [http://www.omim.org/entry/118943 Chymosin pseudogene; CYMP prochymosin, included, in the OMIM]</ref> and [[chicken|chick]]s.<ref name=lineage/>

One study reported finding a chymosin-like enzyme in some human infants,<ref>{{cite journal | vauthors = Henschel MJ, Newport MJ, Parmar V | title = Gastric proteases in the human infant | journal = Biology of the Neonate | volume = 52 | issue = 5 | pages = 268–72 | year = 1987 | pmid = 3118972 | doi = 10.1159/000242719 }}</ref> but others have failed to replicate this finding.<ref>{{cite book | vauthors = Szecsi PB, Harboe M | veditors = Rawlings ND, Salvesen G |year=2013|title=Handbook of Proteolytic Enzymes|chapter=Chapter 5: Chymosin|chapter-url=https://www.researchgate.net/publication/278718218|language=en|volume=1|pages=37–42|doi=10.1016/B978-0-12-382219-2.00005-3}}</ref> Humans have a [[pseudogene]] for chymosin that does not generate a protein, found on [[Chromosome 1 (human)|chromosome 1]].<ref name= OMIM/><ref>{{cite book | vauthors = Fox PF | title = Cheese: Chemistry, Physics and Microbiology | date = 28 February 1999 | publisher = Springer | isbn = 9780834213388 | url = https://books.google.com/books?id=U_mj5DANAeoC&q=chymosin+gene+human&pg=PA62 }}</ref>  Humans have other proteins to digest milk, such as [[pepsin]] and [[lipase]].<ref>{{cite book | vauthors = Sanderson IR, Walker WA |title=Development of the gastrointestinal tract |date=1999 |publisher=B.C. Decker |location=Hamilton, Ontario |isbn=978-1-55009-081-9 | url = https://books.google.com/books?id=YhgKZ_dvda0C }}</ref>{{rp|262}}

In addition to the primate lineage leading up to humans, some other mammals have also lost the chymosin gene.<ref name=lineage>{{cite journal | vauthors = Lopes-Marques M, Ruivo R, Fonseca E, Teixeira A, Castro LF | title = Unusual loss of chymosin in mammalian lineages parallels neo-natal immune transfer strategies | journal = Molecular Phylogenetics and Evolution | volume = 116 | pages = 78–86 | date = November 2017 | pmid = 28851538 | doi = 10.1016/j.ympev.2017.08.014 }}</ref>