Editing Proinsulin (section)

{{short description|Precursor protein in humans}}
{{infobox protein
| Name = insulin
| caption = Insulin undergoes extensive posttranslational modification along the production pathway. Production and secretion are largely independent; prepared insulin is stored awaiting secretion. Both C-peptide and mature insulin are biologically active. Cell components and proteins in this image are not to scale.
| image = Insulin path.svg
| width = 220px
| HGNCid = 6081
| Symbol = INS
| AltSymbols =
| EntrezGene = 3630
| OMIM =  176730
| RefSeq = NM_000207
| UniProt =  P01308
| PDB =
| ECnumber =
| Chromosome = 11
| Arm = p
| Band = 15.5
| LocusSupplementaryData =
}}
'''Proinsulin''' is the [[prohormone]] precursor to [[insulin]] made in the [[beta cell]]s of the [[Pancreatic islets|Pancreatic Islets]], specialized regions of the [[pancreas]]. In humans, proinsulin is encoded by the ''INS'' [[gene]].<ref name="entrez">{{cite web | title = Entrez Gene: INS insulin| url =https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=3630| access-date = }}</ref><ref name="pmid6243748">{{cite journal | vauthors = Bell GI, Pictet RL, Rutter WJ, Cordell B, Tischer E, Goodman HM | title = Sequence of the human insulin gene | journal = Nature | volume = 284 | issue = 5751 | pages = 26–32 | date = March 1980 | pmid = 6243748 | doi = 10.1038/284026a0 | bibcode = 1980Natur.284...26B | s2cid = 4363706 }}</ref> The pancreatic islets only secrete between 1% and 3% of proinsulin intact.<ref name="Mayo_Medical">{{Cite web |url= http://www.mayomedicallaboratories.com/interpretive-guide/?alpha=P&unit_code=80908 |title= Interpretation for 80908 Proinsulin, Plasma |website= www.mayomedicallaboratories.com |access-date= 2017-03-09 |archive-date= 2017-10-04 |archive-url= https://web.archive.org/web/20171004085449/https://www.mayomedicallaboratories.com/interpretive-guide/?alpha=P&unit_code=80908 |url-status= dead }}</ref> However, because proinsulin has a longer half life than insulin, it can account for anywhere from 5–30% of the insulin-like structures circulating in the blood.<ref name="Mayo_Medical" /> There are higher concentrations of proinsulin after meals and lower levels when a person is fasting.<ref name="Mayo_Medical" /> Additionally, while proinsulin and insulin have structural differences, proinsulin does demonstrate some affinity for the [[insulin receptor]]. Due to the relative similarities in structure, proinsulin can produce between 5% and 10% of the metabolic activity similarly induced by insulin.<ref name="Mayo_Medical" />

Proinsulin is the final single chain protein structure secreted by cells before cleavage into mature insulin.<ref>{{cite journal | vauthors = Assali NS, Clark KE, Zugaib M, Brinkman CR, Nuwayhid B | title = Effects of estrogenic hormones on uteroplacental hemodynamics and progesterone production in the sheep | journal = International Journal of Fertility | volume = 23 | issue = 3 | pages = 219–23 | year = 1995 | pmid= 40897 | pmc = 8333766 }}</ref> Proinsulin was discovered by Professor [[Donald F. Steiner]] of the University of Chicago in 1967.<ref>{{cite journal | vauthors = Philipson LH, Bell G, Polonsky KS | title = Donald F. Steiner MD, 1930-2014: discoverer of proinsulin | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 4 | pages = 940–1 | date = January 2015 | pmid = 25561547 | pmc = 4313841 | doi = 10.1073/pnas.1423774112 | bibcode = 2015PNAS..112..940P | doi-access = free }}</ref>