Editing Peptide (section)

== Classification ==
There are numerous types of peptides that have been classified according to their sources and functions. According to the ''Handbook of Biologically Active Peptides'', some groups of peptides include plant peptides, bacterial/[[Antimicrobial peptides|antibiotic peptide]]s, fungal peptides, invertebrate peptides, amphibian/skin peptides, venom peptides, cancer/anticancer peptides, vaccine peptides, immune/inflammatory peptides, brain peptides, [[peptide hormones|endocrine peptide]]s, ingestive peptides, gastrointestinal peptides, cardiovascular peptides, renal peptides, respiratory peptides, [[opioid peptide]]s, [[neurotrophic]] peptides, and blood–brain peptides.<ref>{{Cite book |title=Handbook of Biologically Active Peptides |publisher=Elsevier Science |year=2013 |isbn=978-0-12-385095-9 |editor-last=Abba J. Kastin |edition=2nd}}</ref>

Some ribosomal peptides are subject to [[proteolysis]]. These function, typically in higher organisms, as [[hormone]]s and signaling molecules. Some microbes produce peptides as [[antibiotic]]s, such as [[microcin]]s and [[bacteriocin]]s.<ref>{{Cite journal |vauthors=Duquesne S, Destoumieux-Garzón D, Peduzzi J, Rebuffat S |date=August 2007 |title=Microcins, gene-encoded antibacterial peptides from enterobacteria |journal=Natural Product Reports |volume=24 |issue=4 |pages=708–34 |doi=10.1039/b516237h |pmid=17653356}}</ref>

Peptides frequently have [[post-translational modification]]s such as [[phosphorylation]], [[hydroxylation]], [[sulfonation]], [[palmitoylation]], glycosylation, and [[disulfide bridge|disulfide]] formation. In general, peptides are linear, although [[splicing (genetics)|lariat]] structures have been observed.<ref>{{Cite journal |vauthors=Pons M, Feliz M, Antònia Molins M, Giralt E |date=May 1991 |title=Conformational analysis of bacitracin A, a naturally occurring lariat |journal=Biopolymers |volume=31 |issue=6 |pages=605–12 |doi=10.1002/bip.360310604 |pmid=1932561 |s2cid=10924338}}</ref> More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in [[platypus venom]].<ref>{{Cite journal |vauthors=Torres AM, Menz I, Alewood PF, etal |date=July 2002 |title=D-Amino acid residue in the C-type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus |journal=FEBS Letters |volume=524 |issue=1–3 |pages=172–6 |bibcode=2002FEBSL.524..172T |doi=10.1016/S0014-5793(02)03050-8 |pmid=12135762 |s2cid=3015474}}</ref>

''[[Nonribosomal peptide]]s'' are assembled by [[enzyme]]s, not the ribosome. A common non-ribosomal peptide is [[glutathione]], a component of the [[antioxidant]] defenses of most aerobic organisms.<ref name="MeisterB">{{Cite journal |last=Meister A, Anderson ME |last2=Anderson |year=1983 |title=Glutathione |journal=Annual Review of Biochemistry |volume=52 |issue=1 |pages=711–60 |doi=10.1146/annurev.bi.52.070183.003431 |pmid=6137189}}</ref> Other nonribosomal peptides are most common in [[unicellular organism]]s, [[plant]]s, and [[fungi]] and are synthesized by [[Modularity (biology)|modular]] enzyme complexes called ''nonribosomal peptide synthetases''.<ref>{{Cite journal |last=Hahn M, Stachelhaus T |last2=Stachelhaus |date=November 2004 |title=Selective interaction between nonribosomal peptide synthetases is facilitated by short communication-mediating domains |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=101 |issue=44 |pages=15585–90 |bibcode=2004PNAS..10115585H |doi=10.1073/pnas.0404932101 |pmc=524835 |pmid=15498872 |doi-access=free}}</ref>

These complexes are often laid out in a similar fashion, and they can contain many different modules to perform a diverse set of chemical manipulations on the developing product.<ref>{{Cite journal |last=Finking R, Marahiel MA |last2=Marahiel |year=2004 |title=Biosynthesis of nonribosomal peptides1 |journal=Annual Review of Microbiology |volume=58 |issue=1 |pages=453–88 |doi=10.1146/annurev.micro.58.030603.123615 |pmid=15487945}}</ref> These peptides are often [[Cyclic compound|cyclic]] and can have highly complex cyclic structures, although linear nonribosomal peptides are also common. Since the system is closely related to the machinery for building [[fatty acid]]s and [[polyketide]]s, hybrid compounds are often found. The presence of [[oxazoles]] or [[thiazoles]] often indicates that the compound was synthesized in this fashion.<ref>{{Cite journal |last=Du L, Shen B |last2=Shen |date=March 2001 |title=Biosynthesis of hybrid peptide-polyketide natural products |journal=Current Opinion in Drug Discovery & Development |volume=4 |issue=2 |pages=215–28 |pmid=11378961}}</ref>

''{{vanchor|Peptones}}'' are derived from animal milk or meat digested by [[proteolysis]].<ref>{{Cite web |title=UsvPeptides- USVPeptides is a leading pharmaceutical company in India |url=http://www.usvpeptides.com |website=USVPeptides}}</ref> In addition to containing small peptides, the resulting material includes fats, metals, salts, vitamins, and many other biological compounds. Peptones are used in nutrient media for growing bacteria and fungi.<ref>{{Cite book |last=Payne |first=J. W. |title=Advances in Microbial Physiology, Volume 13 |last2=Rose |first2=Anthony H. |last3=Tempest |first3=D. W. |date=27 September 1974 |publisher=Elsevier Science |isbn=978-0-08-057971-9 |volume=13 |location=Oxford, England |pages=55–160 |chapter=Peptides and micro-organisms |doi=10.1016/S0065-2911(08)60038-7 |oclc=1049559483 |pmid=775944 |chapter-url=https://books.google.com/books?id=QgQuTYSW8A4C&dq=peptides&pg=PA147}}</ref>

''Peptide fragments'' refer to fragments of proteins that are used to identify or quantify the source protein.<ref>{{Cite journal |vauthors=Hummel J, Niemann M, Wienkoop S, Schulze W, Steinhauser D, Selbig J, Walther D, Weckwerth W |year=2007 |title=ProMEX: a mass spectral reference database for proteins and protein phosphorylation sites |journal=BMC Bioinformatics |volume=8 |issue=1 |page=216 |doi=10.1186/1471-2105-8-216 |pmc=1920535 |pmid=17587460 |doi-access=free}}</ref> Often these are the products of enzymatic degradation performed in the laboratory on a controlled sample, but can also be forensic or paleontological samples that have been degraded by natural effects.<ref>{{Cite book |last=Webster J, Oxley D |title=Chemical Genomics |last2=Oxley |year=2005 |isbn=978-1-58829-399-2 |series=Methods in Molecular Biology |volume=310 |pages=227–40 |chapter=Peptide Mass Fingerprinting |doi=10.1007/978-1-59259-948-6_16 |pmid=16350956 |chapter-url=https://archive.org/details/chemicalgenomics00zand_0/page/227 |chapter-url-access=registration}}</ref><ref>{{Cite journal |last=Marquet P, Lachâtre G |last2=Lachâtre |date=October 1999 |title=Liquid chromatography-mass spectrometry: potential in forensic and clinical toxicology |journal=Journal of Chromatography B |volume=733 |issue=1–2 |pages=93–118 |doi=10.1016/S0378-4347(99)00147-4 |pmid=10572976}}</ref>