Peptide

{{Short description|Short chains of 2–50 amino acids}} {{for|peptides used medically|Peptide therapeutics}} {{Redirect|Peptides|the journal|Peptides (journal)}} [[File:Drosomycin.svg|thumb|Drosomycin, an example of a peptide]]

'''Peptides''' are short chains of amino acids linked by peptide bonds.<ref>{{Cite book |last=Hamley |first=I. W. |url=https://www.wiley.com/en-ai/Introduction+to+Peptide+Science-p-9781119698173 |title=introduction to Peptide Science |date=September 2020 |publisher=Wiley |isbn=978-1-119-69817-3}}</ref><ref>{{Lehninger4th}}</ref> A '''polypeptide''' is a longer, continuous, unbranched peptide chain.<ref name="Saladin">{{Cite book |last=Saladin |first=K. |title=Anatomy & physiology: the unity of form and function |date=13 January 2011 |publisher=McGraw-Hill |isbn=978-0-07-337825-1 |edition=6th |page=67}}</ref> Polypeptides that have a molecular mass of 10,000 Da or more are called proteins.<ref>{{GoldBookRef |title=proteins |file=P04898}}.</ref> Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.<ref>{{Cite journal |last1=Ardejani |first1=Maziar S. |last2=Orner |first2=Brendan P. |date=2013-05-03 |title=Obey the Peptide Assembly Rules |journal=Science |volume=340 |issue=6132 |pages=561–562 |bibcode=2013Sci...340..561A |doi=10.1126/science.1237708 |issn=0036-8075 |pmid=23641105 |s2cid=206548864}}</ref>

Amino acids comprise peptides as residues.<ref name="IUPAC1">{{GoldBookRef|file=A00279|title=amino-acid residue in a polypeptide}}.</ref> Peptides are usually "linear" with an N-terminal (amine group) and C-terminal (carboxyl group) residue at the ends. Cyclic peptides are a distinct class.

== Classification == Peptides have been classified according to their sources and functions.<ref>{{Cite book |last=Hamley |first=I. W. |url=https://www.wiley.com/en-ai/Introduction+to+Peptide+Science-p-9781119698173 |title=introduction to Peptide Science |date=September 2020 |publisher=Wiley |isbn=978-1-119-69817-3}} {{Cite book |last=Hamley |first=I. W. |url=https://www.wiley.com/en-ai/Introduction+to+Peptide+Science-p-9781119698173 |title=introduction to Peptide Science |date=September 2020 |publisher=Wiley |isbn=978-1-119-69817-3}}</ref> Some groups of peptides include plant peptides, bacterial/antibiotic peptides, fungal peptides, invertebrate peptides, amphibian/skin peptides, venom peptides, cancer/anticancer peptides, vaccine peptides, immune/inflammatory peptides, brain peptides, endocrine peptides, ingestive peptides, gastrointestinal peptides, cardiovascular peptides, renal peptides, respiratory peptides, opioid peptides, 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 hormones and signaling molecules. Some microbes produce peptides as antibiotics, such as microcins and bacteriocins.<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 modifications such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation, and disulfide formation. In general, peptides are linear, although 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 peptides'' are assembled by enzymes, 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 |last1=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 organisms, plants, and fungi and are synthesized by modular enzyme complexes called ''nonribosomal peptide synthetases''.<ref>{{Cite journal |last1=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>

{{anchor|Peptone}} 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 |last1=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 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 acids and polyketides, hybrid compounds are often found. The presence of oxazoles or thiazoles often indicates that the compound was synthesized in this fashion.<ref>{{Cite journal |last1=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>

'''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 |last1=Payne |first1=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 |journal=Advances in Microbial Physiology |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 |article-number=216 |doi=10.1186/1471-2105-8-216 |pmc=1920535 |pmid=17587460 |doi-access=free |bibcode=2007BMCBi...8..216H }}</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 |last1=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 |last1=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>

== Chemical synthesis == {{Main|Peptide synthesis}} [[File:Peptide Synthesis.svg|thumb|centre|upright=3.0|alt=Table of amino acids| Solid-phase peptide synthesis on a rink amide resin using Fmoc-α-amine-protected amino acid]]

== Protein–peptide interactions == thumb|Example of a protein (orange) and peptide (green) interaction. Obtained from Propedia: a peptide-protein interactions database.<ref>{{Cite web |title=Propedia v2.3 - Peptide-Protein Interactions Database |url=http://bioinfo.dcc.ufmg.br/propedia2/ |access-date=2023-03-28 |website=bioinfo.dcc.ufmg.br}}</ref> Peptides can perform interactions with proteins and other macromolecules. They are responsible for numerous important functions in human cells, such as cell signaling, and act as immune modulators.<ref name=":0">{{Cite journal |last1=Martins |first1=Pedro M. |last2=Santos |first2=Lucianna H. |last3=Mariano |first3=Diego |last4=Queiroz |first4=Felippe C. |last5=Bastos |first5=Luana L. |last6=Gomes |first6=Isabela de S. |last7=Fischer |first7=Pedro H. C. |last8=Rocha |first8=Rafael E. O. |last9=Silveira |first9=Sabrina A. |last10=de Lima |first10=Leonardo H. F. |last11=de Magalhães |first11=Mariana T. Q. |last12=Oliveira |first12=Maria G. A. |last13=de Melo-Minardi |first13=Raquel C. |date=December 2021 |title=Propedia: a database for protein–peptide identification based on a hybrid clustering algorithm |journal=BMC Bioinformatics |language=en |volume=22 |issue=1 |article-number=1 |doi=10.1186/s12859-020-03881-z |issn=1471-2105 |pmc=7776311 |pmid=33388027 |doi-access=free}}</ref> Indeed, studies have reported that 15-40% of all protein–protein interactions in human cells are mediated by peptides.<ref>{{Cite journal |last1=Neduva |first1=Victor |last2=Linding |first2=Rune |last3=Su-Angrand |first3=Isabelle |last4=Stark |first4=Alexander |last5=Masi |first5=Federico de |last6=Gibson |first6=Toby J |last7=Lewis |first7=Joe |last8=Serrano |first8=Luis |last9=Russell |first9=Robert B |date=2005-11-15 |editor-last=Matthews |editor-first=Rowena |title=Systematic Discovery of New Recognition Peptides Mediating Protein Interaction Networks |journal=PLOS Biology |language=en |volume=3 |issue=12 |article-number=e405 |doi=10.1371/journal.pbio.0030405 |issn=1545-7885 |pmc=1283537 |pmid=16279839 |doi-access=free}}</ref> Additionally, it is estimated that at least 10% of the pharmaceutical market is based on peptide products.<ref name=":0" /> == Applications of machine learning in peptide prediction == Machine learning and deep learning architectures are extensively utilized to classify, screen, and design peptides based on sequence- and structure-derived data.<ref name="Wang2023">{{Cite journal |last1=Wang |first1=Jiaqi |last2=Liu |first2=Zihan |last3=Zhao |first3=Shuang |date=November 2023 |title=Deep Learning Empowers the Discovery of Self-Assembling Peptides with Over 10 Trillion Sequences |journal=Advanced Science |volume=10 |issue=31 |article-number=2301544 |doi=10.1002/advs.202301544 |pmid=37749875 |pmc=10625107 }}</ref><ref name="Brizuela2025">{{cite journal |last1=Brizuela |first1=Carlos A. |last2=Liu |first2=Gary |last3=Stokes |first3=Jonathan M. |last4=de la Fuente-Nunez |first4=Cesar |title=AI methods for antimicrobial peptides: progress and challenges |journal=Microbial Biotechnology |year=2025 |volume=18 |issue=1 |article-number=e70072 |doi=10.1111/1751-7915.70072 |pmid=39754551 |pmc=11702388 }}</ref> These computational approaches are particularly valuable when experimental screening is cost-prohibitive, time-consuming, or difficult to scale. A standard workflow typically involves dataset curation, the transformation of peptide sequences or structures into numerical features, model optimization, and rigorous performance validation.<ref name="Asim2025">{{cite journal |last1=Asim |first1=Muhammad Nabeel |last2=Asif |first2=Tayyaba |last3=Mehmood |first3=Faiza |last4=Dengel |first4=Andreas |title=Peptide classification landscape: an in-depth systematic literature review |journal=Computers in Biology and Medicine |year=2025 |volume=188 |doi=10.1016/j.compbiomed.2025.109821 |pmid=39987697 }}</ref> Commonly used representations include amino acid composition, physicochemical descriptors, substitution matrices, and learned embeddings derived from protein or peptide language models.<ref name="Asim2025" /><ref name="Erckes2026">{{cite journal |last1=Erckes |first1=Vanessa |last2=Abderrahmane |first2=Massina |last3=Ochoa |first3=Rodrigo |title=Peptide cheminformatics tools: making computational tasks accessible in peptide drug discovery |journal=Drug Discovery Today |year=2026 |volume=31 |issue=2 |article-number=104612 |doi=10.1016/j.drudis.2026.104612 |pmid=41577169 }}</ref> These methodologies have been successfully applied across various functional classes, such as antimicrobial peptides, cell-penetrating peptides, and anticancer agents.<ref name="Brizuela2025" /><ref name="Asim2025" /> Current challenges in the field include addressing dataset biases, establishing consistent benchmarking protocols, and improving the interpretability of complex "black-box" models.<ref name="Asim2025" /><ref name="Brizuela2025" /> == Molecular properties and chemical space of peptides == The chemical space of peptides is defined as a multidimensional landscape shaped by molecular descriptors or fingerprints. Within these frameworks, the distance between specific molecules serves as a proxy for chemical or functional similarity.<ref name="Orsi2025">{{Cite journal |last1=Orsi |first1=Markus |last2=Reymond |first2=Jean-Louis |date=January 2025 |title=Navigating a 1E+60 Chemical Space of Peptide/Peptoid Oligomers |journal=Molecular Informatics |volume=44 |issue=1 |article-number=e202400186 |doi=10.1002/minf.202400186 |pmid=39390672 |pmc=11733718 }}</ref><ref name="Oliveira2026">{{cite journal |last1=de Oliveira |first1=Ewerton Cristhian Lima |last2=Feio |first2=Juliana Auzier Seixas |last3=Costa |first3=Kauê |title=Navigating in the chemical space of peptides: computational strategies and molecular features |journal=Physical Chemistry Chemical Physics |year=2026 |doi=10.1039/D5CP04611D |pmid=42065516 }}</ref> This space can be mapped using primary amino acid sequences, three-dimensional structural data, or a combination of both. Key molecular properties used for mapping include molecular weight, lipophilicity (logP and logD), topological polar surface area (TPSA), and hydrogen-bond dynamics.<ref name="Oliveira2026" /><ref name="Descamps2025">{{Cite journal |last1=Descamps |first1=Amélie |last2=Hirmz |first2=Hannah |last3=Wynendaele |first3=Evelien |date=2025-07-01 |title=Beyond Molecular Weight: Peptide Characteristics Influencing the Sensitivity of Retention |journal=ACS Omega |volume=10 |issue=25 |pages=27089–27097 |doi=10.1021/acsomega.5c02327 |doi-access=free |pmid=40621014 |pmc=12223815 }}</ref> Dimensionality-reduction techniques—such as Principal Component Analysis (PCA), t-SNE, and UMAP—are frequently employed alongside clustering algorithms to visualize peptide libraries and identify clusters with related biological activities.<ref name="Romero2025">{{Cite journal |last1=Romero |first1=Maylin |last2=Marrero-Ponce |first2=Yovani |date=2025-11-18 |title=Half-Space Proximal Networks (HSPNs): A Proxy for Multi-Query Similarity Searching |journal=ACS Omega |volume=10 |issue=45 |pages=54389–54404 |doi=10.1021/acsomega.5c07055 |doi-access=free |pmid=41280784 |pmc=12631478 }}</ref><ref name="Orsi2025" /> Peptides are distinguished from traditional small molecules by their unique combination of residue sequence, amide backbone flexibility, and susceptibility to chemical modifications, all of which dictate bioavailability and membrane permeability.<ref name="Oliveira2026" /> Computational analysis is supported by notation systems like FASTA, HELM, and BILN for encoding both canonical and modified sequences.<ref name="Erckes2026" /> Modifications such as cyclization or the integration of non-natural amino acids significantly shift a peptide's position within the chemical space, altering its stability and target affinity. Consequently, chemical-space analysis is a vital tool for virtual screening and the discovery of shared bioactivity regions across different peptide families.<ref name="Oliveira2026" /><ref name="Erckes2026" />

== Example families == The peptide families in this section are ribosomal peptides, usually with hormonal activity. All of these peptides are synthesized by cells as longer "propeptides" or "proproteins" and truncated prior to exiting the cell. They are released into the bloodstream where they perform their signaling functions.<ref>{{Cite web |date=2025-01-11 |title=Protein Synthesis: From Ribosomes to Post-Translational Modifications |url=https://biologyinsights.com/protein-synthesis-from-ribosomes-to-post-translational-modifications/ |access-date=2025-04-04 |website=BiologyInsights |language=en-US}}</ref>

=== Antimicrobial peptides === * Magainin family * Cecropin family * Cathelicidin family * Defensin family

=== Tachykinin peptides === {{main | Tachykinin peptides}} * Substance P * Kassinin * Neurokinin A * Eledoisin * Neurokinin B

=== Vasoactive intestinal peptides === {{main | Secretin family}} * VIP ('''''V'''asoactive '''I'''ntestinal '''P'''eptide''; PHM27) * PACAP '''''P'''ituitary '''A'''denylate '''C'''yclase '''A'''ctivating '''P'''eptide'' * Peptide PHI 27 ('''''P'''eptide '''H'''istidine '''I'''soleucine 27'') * GHRH 1-24 ''('''G'''rowth '''H'''ormone '''R'''eleasing '''H'''ormone 1-24)'' * Glucagon * Secretin

=== Pancreatic polypeptide-related peptides === * NPY ''('''N'''euro'''P'''eptide '''Y''')'' * PYY ''('''P'''eptide '''YY''')'' * APP ''('''A'''vian '''P'''ancreatic '''P'''olypeptide)'' * PPY ''('''P'''ancreatic '''P'''ol'''Y'''peptide)''

=== Opioid peptides === {{main|Opioid peptide}} * Proopiomelanocortin (POMC) peptides * Enkephalin pentapeptides * Prodynorphin peptides

=== Calcitonin peptides === * Calcitonin * Amylin * AGG01

=== Self-assembling peptides === * Aromatic short peptides<ref>{{Cite journal |last1=Tao |first1=Kai |last2=Makam |first2=Pandeeswar |last3=Aizen |first3=Ruth |last4=Gazit |first4=Ehud |date=17 Nov 2017 |title=Self-assembling peptide semiconductors |journal=Science |volume=358 |issue=6365 |article-number=eaam9756 |doi=10.1126/science.aam9756 |pmc=5712217 |pmid=29146781}}</ref><ref>{{Cite journal |last1=Tao |first1=Kai |last2=Levin |first2=Aviad |last3=Adler-Abramovich |first3=Lihi |last4=Gazit |first4=Ehud |date=26 Apr 2016 |title=Fmoc-modified amino acids and short peptides: simple bio-inspired building blocks for the fabrication of functional materials |journal=Chem. Soc. Rev. |volume=45 |issue=14 |pages=3935–3953 |doi=10.1039/C5CS00889A |pmid=27115033}}</ref> * Biomimetic peptides<ref>{{Cite journal |last1=Tao |first1=Kai |last2=Wang |first2=Jiqian |last3=Zhou |first3=Peng |last4=Wang |first4=Chengdong |last5=Xu |first5=Hai |last6=Zhao |first6=Xiubo |last7=Lu |first7=Jian R. |date=February 10, 2011 |title=Self-Assembly of Short Aβ(16−22) Peptides: Effect of Terminal Capping and the Role of Electrostatic Interaction |journal=Langmuir |volume=27 |issue=6 |pages=2723–2730 |doi=10.1021/la1034273 |pmid=21309606}}</ref> * Peptide amphiphiles<ref>{{Cite journal |last=Ian Hamley |date=2011 |title=Self-Assembly of Amphiphilic Peptides |url=http://centaur.reading.ac.uk/19780/1/AmphPeptReviewRevised.pdf |journal=Soft Matter |volume=7 |issue=9 |pages=4122–4138 |bibcode=2011SMat....7.4122H |doi=10.1039/C0SM01218A}}</ref><ref>{{Cite journal |last1=Kai Tao |last2=Guy Jacoby |last3=Luba Burlaka |last4=Roy Beck |last5=Ehud Gazit |date=July 26, 2016 |title=Design of Controllable Bio-Inspired Chiroptic Self-Assemblies |journal=Biomacromolecules |volume=17 |issue=9 |pages=2937–2945 |doi=10.1021/acs.biomac.6b00752 |pmid=27461453}}</ref><ref>{{Cite journal |last1=Kai Tao |last2=Aviad Levin |last3=Guy Jacoby |last4=Roy Beck |last5=Ehud Gazit |date=23 August 2016 |title=Entropic Phase Transitions with Stable Twisted Intermediates of Bio-Inspired Self-Assembly |journal=Chem. Eur. J. |volume=22 |issue=43 |pages=15237–15241 |doi=10.1002/chem.201603882 |pmid=27550381}}</ref><ref>{{Cite journal |last1=Donghui Jia |last2=Kai Tao |last3=Jiqian Wang |last4=Chengdong Wang |last5=Xiubo Zhao |last6=Mohammed Yaseen |last7=Hai Xu |last8=Guohe Que |last9=John R. P. Webster |last10=Jian R. Lu |date=June 16, 2011 |title=Dynamic Adsorption and Structure of Interfacial Bilayers Adsorbed from Lipopeptide Surfactants at the Hydrophilic Silicon/Water Interface: Effect of the Headgroup Length |journal=Langmuir |volume=27 |issue=14 |pages=8798–8809 |doi=10.1021/la105129m |pmid=21675796}}</ref> * Peptide dendrimers<ref>{{Cite journal |last1=Heitz |first1=Marc |last2=Javor |first2=Sacha |last3=Darbre |first3=Tamis |last4=Reymond |first4=Jean-Louis |date=2019-08-21 |title=Stereoselective pH Responsive Peptide Dendrimers for siRNA Transfection |journal=Bioconjugate Chemistry |language=en |volume=30 |issue=8 |pages=2165–2182 |doi=10.1021/acs.bioconjchem.9b00403 |issn=1043-1802 |pmid=31398014 |s2cid=199519310}}</ref>

=== Other peptides === * B-type Natriuretic Peptide (BNP) – produced in the myocardium and useful in medical diagnosis * Lactotripeptides – Lactotripeptides might reduce blood pressure,<ref>{{Cite journal |last1=Boelsma E, Kloek J |last2=Kloek |date=March 2009 |title=Lactotripeptides and antihypertensive effects: a critical review |journal=The British Journal of Nutrition |volume=101 |issue=6 |pages=776–86 |doi=10.1017/S0007114508137722 |pmid=19061526 |doi-access=free}}</ref><ref>{{Cite journal |vauthors=Xu JY, Qin LQ, Wang PY, Li W, Chang C |date=October 2008 |title=Effect of milk tripeptides on blood pressure: a meta-analysis of randomized controlled trials |journal=Nutrition |volume=24 |issue=10 |pages=933–40 |doi=10.1016/j.nut.2008.04.004 |pmid=18562172}}</ref><ref>{{Cite journal |last=Pripp AH |year=2008 |title=Effect of peptides derived from food proteins on blood pressure: a meta-analysis of randomized controlled trials |journal=Food & Nutrition Research |volume=52 |article-number=10.3402/fnr.v52i0.1641 |doi=10.3402/fnr.v52i0.1641 |pmc=2596738 |pmid=19109662}}</ref> although the evidence is mixed.<ref>{{Cite journal |vauthors=Engberink MF, Schouten EG, Kok FJ, van Mierlo LA, Brouwer IA, Geleijnse JM |date=February 2008 |title=Lactotripeptides show no effect on human blood pressure: results from a double-blind randomized controlled trial |journal=Hypertension |volume=51 |issue=2 |pages=399–405 |doi=10.1161/HYPERTENSIONAHA.107.098988 |pmid=18086944 |doi-access=free}}</ref> * Peptidic components from traditional Chinese medicine Colla Corii Asini in hematopoiesis.<ref>{{Cite journal |last1=Wu |first1=Hongzhong |last2=Ren |first2=Chunyan |last3=Yang |first3=Fang |last4=Qin |first4=Yufeng |last5=Zhang |first5=Yuanxing |last6=Liu |first6=Jianwen |date=April 2016 |title=Extraction and identification of collagen-derived peptides with hematopoietic activity from Colla Corii Asini |journal=Journal of Ethnopharmacology |volume=182 |pages=129–136 |doi=10.1016/j.jep.2016.02.019 |pmid=26911525}}</ref> * Jelleine – produced from royal jelly of honey bees.

== Terminology ==

=== Length === Several terms related to peptides have no strict length definitions, and there is often overlap in their usage:{{cn|date=January 2025}} * A ''polypeptide'' is a single linear chain of many amino acids (any length), held together by amide bonds. * A ''protein'' consists of one or more polypeptides (more than about 50 amino acids long). * An ''oligopeptide'' consists of only a few amino acids (between two and twenty).

=== Number of amino acids === [[File:Tripeptide Val-Gly-Ala Formula V1.svg|thumb|upright=1.3|A tripeptide (example Val-Gly-Ala) with '''green''' marked amino end ('''L-valine''') and '''blue''' marked carboxyl end ('''L-alanine''')]]

Peptides and proteins are often described by the number of amino acids in their chain, e.g. a protein with 158 amino acids may be described as a "158 amino-acid-long protein". {{anchor|Notes on terminology"}}Peptides of specific shorter lengths are named using IUPAC numerical multiplier prefixes: * A ''monopeptide'' has one amino acid (not alone but combined with (an)other type(s) of molecule(s)). * A ''dipeptide'' has two amino acids. * A ''tripeptide'' has three amino acids. * A ''tetrapeptide'' has four amino acids. * A ''pentapeptide'' has five amino acids. (''e.g.'', enkephalin). * A ''hexapeptide'' has six amino acids. (''e.g.'', angiotensin IV). * A ''heptapeptide'' has seven amino acids. (''e.g.'', spinorphin). * An ''octapeptide'' has eight amino acids (''e.g.'', angiotensin II). * A ''nonapeptide'' has nine amino acids (''e.g.'', oxytocin). * A ''decapeptide'' has ten amino acids (''e.g.'', gonadotropin-releasing hormone and angiotensin I). * A ''undecapeptide'' has eleven amino acids (''e.g.'', substance P).

The same words are also used to describe a group of residues in a larger polypeptide (''e.g.'', RGD motif).

=== Function === * A ''neuropeptide'' is a peptide that is active in association with neural tissue. * A ''lipopeptide'' is a peptide that has a lipid connected to it, and ''pepducins'' are lipopeptides that interact with GPCRs. * A ''peptide hormone'' is a peptide that acts as a hormone. * A proteose is a mixture of peptides produced by the hydrolysis of proteins. The term is somewhat archaic. * A '''peptidergic agent''' (or drug) is a chemical which functions to directly modulate the peptide systems in the body or brain. An example is opioidergics, which are neuropeptidergics. * A cell-penetrating peptide is a peptide able to penetrate the cell membrane.

== See also == {{Div col|colwidth=20em}} * Acetyl hexapeptide-3 * Beefy meaty peptide * Collagen hybridizing peptide, a short peptide that can bind to denatured collagen in tissues * Bis-peptide * CLE peptide * D-peptide * Epidermal growth factor * ''Journal of Peptide Science'' * Lactotripeptides * Micropeptide * Neuropeptide * Palmitoyl pentapeptide-4 * Pancreatic hormone * peptide spectral library * Peptide synthesis * Peptidomimetics (such as peptoids and β-peptides) to peptides, but with different properties. * Protein tag, describing addition of peptide sequences to enable protein isolation or detection * Replikins * Ribosome * Translation (biology) {{Div col end}}

== References == {{Reflist}}

== External links == * {{Wikiquote-inline}}

Category:Peptides