Editing Casein (section)

== Composition ==
Casein contains a high number of [[proline]] amino acids which hinder the formation of common secondary structural motifs of proteins. There are also no [[disulfide bridge]]s. As a result, it has relatively little [[tertiary structure]]. It is relatively [[hydrophobic]], making it poorly soluble in [[water]]. It is found in milk as a [[suspension (chemistry)|suspension]] of particles, called casein [[micelle]]s, which show only limited resemblance with [[surfactant]]-type micelles in a sense that the [[hydrophilic]] parts reside at the surface and they are spherical. However, in sharp contrast to surfactant micelles, the interior of a casein micelle is highly hydrated. The caseins in the micelles are held together by calcium [[ions]] and hydrophobic interactions. Any of several [[molecular model]]s could account for the special conformation of casein in the micelles.<ref>{{Cite journal|vauthors=Dalgleish DG|date=1998|title=Casein Micelles as Colloids: Surface Structures and Stabilities|journal=[[Journal of Dairy Science|J. Dairy Sci.]]|volume=81|issue=11|pages=3013–8|doi=10.3168/jds.S0022-0302(98)75865-5|doi-access=free}}</ref> One of them proposes the micellar nucleus is formed by several submicelles, the periphery consisting of microvillosities of κ-casein.<ref>{{cite journal | vauthors = Panouillé M, Durand D, Nicolai T, Larquet E, Boisset N | title = Aggregation and gelation of micellar casein particles | journal = Journal of Colloid and Interface Science | volume = 287 | issue = 1 | pages = 85–93 | date = July 2005 | pmid = 15914152 | doi = 10.1016/j.jcis.2005.02.008 | bibcode = 2005JCIS..287...85P }}</ref><ref>{{cite journal | vauthors = Walstra P | title = The voluminosity of bovine casein micelles and some of its implications | journal = The Journal of Dairy Research | volume = 46 | issue = 2 | pages = 317–323 | date = April 1979 | pmid = 469060 | doi = 10.1017/S0022029900017234 | s2cid = 222355860 }}</ref><ref>{{cite journal | vauthors = Lucey JA | title = ADSA Foundation Scholar Award. Formation and physical properties of milk protein gels | journal = Journal of Dairy Science | volume = 85 | issue = 2 | pages = 281–294 | date = February 2002 | pmid = 11913691 | doi = 10.3168/jds.S0022-0302(02)74078-2 | doi-access = free }}</ref> Another model suggests the nucleus is formed by casein-interlinked fibrils.<ref>{{Cite book|title=Advances in Protein Chemistry|vauthors=Holt C|publisher=Academic Press|year=1992|isbn=9780120342433|veditors=Anfinsen CB, Richards FM, Edsall JT, Eisenberg DS|volume=43|pages=63–151|chapter=Structure and Stability of Bovine Casein Micelles|doi=10.1016/S0065-3233(08)60554-9|pmid=1442324|display-editors=3}}</ref>  Finally, the most recent model<ref>{{Cite journal|vauthors=Horne DS|date=1998|title=Casein Interactions: Casting Light on the Black Boxes, the Structure in Dairy Products|journal=International Dairy Journal|volume=8|issue=3|pages=171–7|doi=10.1016/S0958-6946(98)00040-5}}</ref> proposes a double link among the caseins for gelling to take place. All three models consider micelles as [[colloid]]al particles formed by casein aggregates wrapped up in soluble κ-casein molecules.

The [[isoelectric point]] of casein is 4.6. Since milk's pH is 6.6, casein has a negative charge in milk. The purified protein is water-insoluble. While it is also insoluble in neutral salt solutions, it is readily dispersible in dilute [[alkali]]s and in [[salt (chemistry)|salt]] solutions such as aqueous [[sodium oxalate]] and [[sodium acetate]].

The [[enzyme]] [[trypsin]] can [[hydrolysis reaction|hydrolyze]] a [[phosphate]]-containing [[peptone]]. It is used to form a type of organic [[adhesive]].<ref>{{cite web|url=http://www.ccmr.cornell.edu/education/ask/index.html?quid=160|title=Turning milk into homemade moo glue|date=24 Sep 1998|website=Cornell Center for Teaching Innovation|series=Ask A Scientist!|publisher=Cornell University|archive-url=https://web.archive.org/web/20110928023201/http://www.ccmr.cornell.edu/education/ask/index.html?quid=160|archive-date=28 September 2011|url-status=dead|access-date=29 Sep 2011}}</ref>