Peptide - wikipedia Peptide `` Peptides '' redirects here. For the journal, see Peptides ( journal ). A tetrapeptide ( example Val - Gly - Ser - Ala ) with green marked amino end ( L - Valine ) and blue marked carboxyl end ( L - Alanine ). Peptides ( from Gr. : πεπτός, peptós `` digested '' ; derived from πέσσειν, péssein `` to digest '' ) are natural biological or artificially manufactured short chains of amino acid monomers linked by peptide ( amide ) bonds. The covalent chemical bonds are formed when the carboxyl group of one amino acid reacts with the amino group of another. The shortest peptides are dipeptides, consisting of 2 amino acids joined by a single peptide bond, followed by tripeptides, tetrapeptides, etc. A polypeptide is a long, continuous, and unbranched peptide chain. Hence, peptides fall under the broad chemical classes of biological oligomers and polymers, alongside nucleic acids, oligosaccharides and polysaccharides, etc. Peptides are distinguished from proteins on the basis of size, and as an arbitrary benchmark can be understood to contain approximately 50 or fewer amino acids. Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule ( DNA, RNA, etc. ), or to complex macromolecular assemblies. Finally, while aspects of the lab techniques applied to peptides versus polypeptides and proteins differ ( e.g., the specifics of electrophoresis, chromatography, etc. ), the size boundaries that distinguish peptides from polypeptides and proteins are not absolute : long peptides such as amyloid beta have been referred to as proteins, and smaller proteins like insulin have been considered peptides. Amino acids that have been incorporated into peptides are termed `` residues '' due to the release of either a hydrogen ion from the amine end or a hydroxyl ion from the carboxyl end, or both, as a water molecule is released during formation of each amide bond. All peptides except cyclic peptides have an N - terminal and C - terminal residue at the end of the peptide ( as shown for the tetrapeptide in the image ). Contents 1 Peptide classes 2 Peptide synthesis 3 Peptides in molecular biology 4 Well - known peptide families 4.1 Antimicrobial peptides 4.2 Tachykinin peptides 4.3 Vasoactive intestinal peptides 4.4 Pancreatic polypeptide - related peptides 4.5 Opioid peptides 4.6 Calcitonin peptides 4.7 Other peptides 5 Notes on terminology 6 Doping in sports 7 See also 8 References Peptide classes Peptides are divided into several classes, depending on how they are produced : Milk peptides Two naturally occurring milk peptides are formed from the milk protein casein when digestive enzymes break this down ; they can also arise from the proteinases formed by lactobacilli during the fermentation of milk. Ribosomal peptides Ribosomal peptides are synthesized by translation of mRNA. They are often subjected to proteolysis to generate the mature form. These function, typically in higher organisms, as hormones and signaling molecules. Some organisms produce peptides as antibiotics, such as microcins. Since they are translated, the amino acid residues involved are restricted to those utilized by the ribosome. However, these peptides frequently have posttranslational modifications such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation and disulfide formation. In general, they are linear, although lariat structures have been observed. More exotic manipulations do occur, such as racemization of L - amino acids to D - amino acids in platypus venom. Nonribosomal peptides Nonribosomal peptides are assembled by enzymes that are specific to each peptide, rather than by the ribosome. The most common non-ribosomal peptide is glutathione, which is a component of the antioxidant defenses of most aerobic organisms. Other nonribosomal peptides are most common in unicellular organisms, plants, and fungi and are synthesized by modular enzyme complexes called nonribosomal peptide synthetases. 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. 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. Peptones See also : Tryptone Peptones are derived from animal milk or meat digested by proteolysis. 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. Peptide fragments Peptide fragments refer to fragments of proteins that are used to identify or quantify the source protein. 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. Peptide synthesis Main article : Peptide synthesis Solid - phase peptide synthesis on a rink amide resin using Fmoc - α - amine - protected amino acid Peptides in Molecular biology Peptides received prominence in molecular biology for several reasons. The first is that peptides allow the creation of peptide antibodies in animals without the need of purifying the protein of interest. This involves synthesizing antigenic peptides of sections of the protein of interest. These will then be used to make antibodies in a rabbit or mouse against the protein. Another reason is that peptides have become instrumental in mass spectrometry, allowing the identification of proteins of interest based on peptide masses and sequence. Peptides have recently been used in the study of protein structure and function. For example, synthetic peptides can be used as probes to see where protein - peptide interactions occur - see the page on Protein tags. Inhibitory peptides are also used in clinical research to examine the effects of peptides on the inhibition of cancer proteins and other diseases. For example, one of the most promising application is through peptides that target LHRH. These particular peptides act as an agonist, meaning that they bind to a cell in a way that regulates LHRH receptors. The process of inhibiting the cell receptors suggests that peptides could be beneficial in treating prostate cancer. However, additional investigations and experiments are required before the cancer - fighting attributes, exhibited by peptides, can be considered definitive. Well - known peptide 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. Antimicrobial peptides Magainin family Cecropin family Cathelicidin family Defensin family Tachykinin peptides Main article : Tachykinin peptides Substance P Kassinin Neurokinin A Eledoisin Neurokinin B Vasoactive intestinal peptides Main article : Secretin family VIP ( Vasoactive Intestinal Peptide ; PHM27 ) PACAP Pituitary Adenylate Cyclase Activating Peptide Peptide PHI 27 ( Peptide Histidine Isoleucine 27 ) GHRH 1 - 24 ( Growth Hormone Releasing Hormone 1 - 24 ) Glucagon Secretin Pancreatic polypeptide - related peptides NPY ( NeuroPeptide Y ) PYY ( Peptide YY ) APP ( Avian Pancreatic Polypeptide ) PPY Pancreatic PolYpeptide Opioid peptides Main article : Opioid peptide Proopiomelanocortin ( POMC ) peptides Enkephalin pentapeptides Prodynorphin peptides Calcitonin peptides Calcitonin Amylin AGG01 Other peptides B - type Natriuretic Peptide ( BNP ) - produced in myocardium & useful in medical diagnosis Lactotripeptides - Lactotripeptides might reduce blood pressure, although the evidence is mixed. Notes on Terminology Length : A polypeptide is a single linear chain of many amino acids, 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 ). A tripeptide ( example Val - Gly - Ala ) with green marked amino end ( L - Valine ) and blue marked carboxyl end ( L - Alanine ) Number of amino acids : A monopeptide has one amino acid. A dipeptide has two amino acids. A tripeptide has three amino acids. A tetrapeptide has four amino acids. A pentapeptide has five amino acids. A hexapeptide has six amino acids. A heptapeptide has seven amino acids. 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 & angiotensin I ). An undecapeptide ( or monodecapeptide ) has eleven amino acids, a dodecapeptide ( or didecapeptide ) has twelve amino acids, a tridecapeptide has thirteen amino acids, and so forth. An icosapeptide has twenty amino acids, a tricontapeptide has thirty amino acids, a tetracontapeptide has forty amino acids, and so forth. See also : IUPAC numerical multiplier 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. Doping in sports The term peptide has been used to mean secretagogue peptides and peptide hormones in sports doping matters : secretagogue peptides are classified as Schedule 2 ( S2 ) prohibited substances on the World Anti-Doping Agency ( WADA ) Prohibited List, and are therefore prohibited for use by professional athletes both in and out of competition. Such secretagogue peptides have been on the WADA prohibited substances list since at least 2008. The Australian Crime Commission cited the alleged misuse of secretagogue peptides in Australian sport including growth hormone releasing peptides CJC - 1295, GHRP - 6, and GHSR ( gene ) hexarelin. There is ongoing controversy on the legality of using secretagogue peptides in sports. See also Wikiquote has quotations related to : Peptide Argireline Beefy meaty peptide Bis - peptide CLE peptide Epidermal growth factor Journal of Peptide Science Lactotripeptides Multifunctional peptides Neuropeptides 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 References Jump up ^ IUPAC. Compendium of Chemical Terminology, 2nd ed. ( the `` Gold Book '' ). Compiled by A.D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford ( 1997 ). XML on - line corrected version : http://goldbook.iupac.org ( 2006 - ) created by M. Nic, J. Jirat, B. Kosata ; updates compiled by A. Jenkins. ISBN 0 - 9678550 - 9 - 8. doi : 10.1351 / goldbook. P04898. Jump up ^ `` What are peptides ''. Zealand Pharma A / S. Archived from the original on 2014 - 07 - 14. Jump up ^ Ardejani, Maziar S. ; Orner, Brendan P. ( 2013 - 05 - 03 ). `` Obey the Peptide Assembly Rules ''. Science. 340 ( 6132 ) : 561 -- 562. Bibcode : 2013Sci... 340... 561A. ISSN 0036 - 8075. PMID 23641105. doi : 10.1126 / science. 1237708. Jump up ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. ( the `` Gold Book '' ) ( 1997 ). Online corrected version : ( 2006 -- ) `` amino - acid residue in a polypeptide ''. Jump up ^ Haque, Emily ; Chand, Rattan. `` Milk protein derived bioactive peptides ''. Dairy Science. Retrieved 28 July 2014. Jump up ^ Duquesne S, Destoumieux - Garzón D, Peduzzi J, Rebuffat S ; Destoumieux - Garzón ; Peduzzi ; Rebuffat ( August 2007 ). `` Microcins, gene - encoded antibacterial peptides from enterobacteria ''. Natural Product Reports. 24 ( 4 ) : 708 -- 34. PMID 17653356. doi : 10.1039 / b516237h. CS1 maint : Multiple names : authors list ( link ) Jump up ^ Pons M, Feliz M, Antònia Molins M, Giralt E ; Feliz ; Antònia Molins ; Giralt ( May 1991 ). `` Conformational analysis of bacitracin A, a naturally occurring lariat ''. Biopolymers. 31 ( 6 ) : 605 -- 12. PMID 1932561. doi : 10.1002 / bip. 360310604. CS1 maint : Multiple names : authors list ( link ) Jump up ^ Torres AM, Menz I, Alewood PF, et al. ( July 2002 ). `` D - Amino acid residue in the C - type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus ''. FEBS Letters. 524 ( 1 -- 3 ) : 172 -- 6. PMID 12135762. doi : 10.1016 / S0014 - 5793 ( 02 ) 03050 - 8. Jump up ^ Meister A, Anderson ME ; Anderson ( 1983 ). `` Glutathione ''. Annual Review of Biochemistry. 52 ( 1 ) : 711 -- 60. PMID 6137189. doi : 10.1146 / annurev. bi. 52.070183. 003431. Jump up ^ Hahn M, Stachelhaus T ; Stachelhaus ( November 2004 ). `` Selective interaction between nonribosomal peptide synthetases is facilitated by short communication - mediating domains ''. Proceedings of the National Academy of Sciences of the United States of America. 101 ( 44 ) : 15585 -- 90. Bibcode : 2004PNAS... 10115585H. PMC 524835. PMID 15498872. doi : 10.1073 / pnas. 0404932101. Jump up ^ Finking R, Marahiel MA ; Marahiel ( 2004 ). `` Biosynthesis of nonribosomal peptides1 ''. Annual Review of Microbiology. 58 ( 1 ) : 453 -- 88. PMID 15487945. doi : 10.1146 / annurev. micro. 58.030603. 123615. Jump up ^ Du L, Shen B ; Shen ( March 2001 ). `` Biosynthesis of hybrid peptide - polyketide natural products ''. Current Opinion in Drug Discovery & Development. 4 ( 2 ) : 215 -- 28. PMID 11378961. Jump up ^ http://www.usvpeptides.com Jump up ^ Payne JW ( 1976 ). `` Peptides and micro-organisms ''. Advances in Microbial Physiology. Advances in Microbial Physiology. 13 : 55 -- 113. ISBN 9780120277131. PMID 775944. doi : 10.1016 / S0065 - 2911 ( 08 ) 60038 - 7. Jump up ^ Hummel J, Niemann M, Wienkoop S ; et al. ( 2007 ). `` ProMEX : a mass spectral reference database for proteins and protein phosphorylation sites ''. BMC Bioinformatics. 8 ( 1 ) : 216. PMC 1920535. PMID 17587460. doi : 10.1186 / 1471 - 2105 - 8 - 216. CS1 maint : Multiple names : authors list ( link ) CS1 maint : Explicit use of et al. ( link ) Jump up ^ Webster J, Oxley D ; Oxley ( 2005 ). `` Peptide mass fingerprinting : protein identification using MALDI - TOF mass spectrometry ''. Methods in Molecular Biology. Methods in Molecular Biology TM. 310 : 227 -- 40. ISBN 978 - 1 - 58829 - 399 - 2. PMID 16350956. doi : 10.1007 / 978 - 1 - 59259 - 948 - 6_16. Jump up ^ Marquet P, Lachâtre G ; Lachâtre ( October 1999 ). `` Liquid chromatography - mass spectrometry : potential in forensic and clinical toxicology ''. Journal of Chromatography B. 733 ( 1 -- 2 ) : 93 -- 118. PMID 10572976. doi : 10.1016 / S0378 - 4347 ( 99 ) 00147 - 4. Jump up ^ Bulinski JC ( 1986 ). `` Peptide antibodies : new tools for cell biology ''. International Review of Cytology. International Review of Cytology. 103 : 281 -- 302. ISBN 9780123645036. PMID 2427468. doi : 10.1016 / S0074 - 7696 ( 08 ) 60838 - 4. Jump up ^ Herce, Henry D. ; Deng, Wen ; Helma, Jonas ; Leonhardt, Heinrich ; Cardoso, M. Cristina ( 24 October 2013 ). `` Visualization and targeted disruption of protein interactions in living cells ''. Nature Communications. 4. Bibcode : 2013NatCo... 4E2660H. PMC 3826628. PMID 24154492. doi : 10.1038 / ncomms3660. Jump up ^ `` Hormone ( androgen deprivation ) therapy for prostate cancer ''. cancer.org. Retrieved 3 October 2013. Jump up ^ Kumar, Ravi ; Barqawi, A ; Crawford, ED ( 2005 ). `` Adverse Events Associated with Hormonal Therapy for Prostate Cancer ''. Reviews in Urology. 7 ( 5 ) : 37 -- 43. PMC 1477613. PMID 16985883. Jump up ^ Boelsma E, Kloek J ; Kloek ( March 2009 ). `` Lactotripeptides and antihypertensive effects : a critical review ''. The British Journal of Nutrition. 101 ( 6 ) : 776 -- 86. PMID 19061526. doi : 10.1017 / S0007114508137722. Jump up ^ Xu JY, Qin LQ, Wang PY, Li W, Chang C ; Qin ; Wang ; Li ; Chang ( October 2008 ). `` Effect of milk tripeptides on blood pressure : a meta - analysis of randomized controlled trials ''. Nutrition. 24 ( 10 ) : 933 -- 40. PMID 18562172. doi : 10.1016 / j. nut. 2008.04. 004. CS1 maint : Multiple names : authors list ( link ) Jump up ^ Pripp AH ( 2008 ). `` Effect of peptides derived from food proteins on blood pressure : a meta - analysis of randomized controlled trials ''. Food & Nutrition Research. 52 : 10.3402 / fnr. v52i0. 1641. PMC 2596738. PMID 19109662. doi : 10.3402 / fnr. v52i0. 1641. Jump up ^ Engberink MF, Schouten EG, Kok FJ, van Mierlo LA, Brouwer IA, Geleijnse JM ; Schouten ; Kok ; Van Mierlo ; Brouwer ; Geleijnse ( February 2008 ). `` Lactotripeptides show no effect on human blood pressure : results from a double - blind randomized controlled trial ''. Hypertension. 51 ( 2 ) : 399 -- 405. PMID 18086944. doi : 10.1161 / HYPERTENSIONAHA. 107.098988. CS1 maint : Multiple names : authors list ( link ) Jump up ^ https://theconversation.edu.au/we-need-an-advocate-against-asadas-power-in-doping-control-12119 Hormones Endocrine glands Hypothalamic - pituitary Hypothalamus GnRH TRH Dopamine CRH GHRH Somatostatin ( GHIH ) MCH Posterior pituitary Oxytocin Vasopressin Anterior pituitary FSH LH TSH Prolactin POMC CLIP ACTH MSH Endorphins Lipotropin GH Adrenal axis Adrenal cortex aldosterone cortisol cortisone DHEA DHEA - S androstenedione Adrenal medulla epinephrine norepinephrine Thyroid Thyroid hormone Calcitonin Thyroid axis Parathyroid PTH Gonadal axis Testis testosterone AMH inhibin Ovary estradiol progesterone activin and inhibin relaxin ( pregnancy ) Placenta hCG HPL estrogen progesterone Pancreas glucagon insulin amylin somatostatin pancreatic polypeptide Pineal gland melatonin N, N - dimethyltryptamine 5 - methoxy - N, N - dimethyltryptamine Other Thymus Thymosins Thymosin α1 Beta thymosins Thymopoietin Thymulin Digestive system Stomach gastrin ghrelin Duodenum CCK Incretins GIP GLP - 1 secretin motilin VIP Ileum enteroglucagon peptide YY Liver / other Insulin - like growth factor IGF - 1 IGF - 2 Adipose tissue leptin adiponectin resistin Skeleton Osteocalcin Kidney JGA ( renin ) peritubular cells EPO calcitriol prostaglandin Heart Natriuretic peptide ANP BNP Signaling peptide / protein receptor modulators Adiponectin AdipoR Agonists : Peptide : Adiponectin ADP - 355 ADP - 399 ; Non-peptide : AdipoRon ( -- ) - Arctigenin Arctiin Gramine Matairesinol Antagonists : Peptide : ADP - 400 AdipoR Agonists : Peptide : Adiponectin ADP - 355 ADP - 399 ; Non-peptide : AdipoRon Deoxyschizandrin Parthenolide Syringing Taxifoliol Antagonists : Peptide : ADP - 400 Angiotensin See here instead. Bradykinin Agonists : Bradykinin Kallidin Antagonists : FR - 173657 Icatibant LF22 - 0542 CGRP Agonists : Amylin CGRP Pramlintide Antagonists : Atogepant BI 44370 TA CGRP ( 8 - 37 ) MK - 3207 Olcegepant Rimegepant SB - 268262 Telcagepant Ubrogepant Antibodies : Erenumab Cholecystokinin CCK Agonists : Cholecystokinin Antagonists : Amiglumide Asperlicin Devazepide Dexloxiglumide Lintitript Lorglumide Loxiglumide Pranazepide Proglumide Tarazepide Tomoglumide CCK Agonists : Cholecystokinin CCK - 4 Gastrin Pentagastrin ( CCK - 5 ) Antagonists : Ceclazepide CI - 988 ( PD - 134308 ) Itriglumide L - 365,360 Netazepide Proglumide Spiroglumide Unsorted Antagonists : Nastorazepide CRH CRF Agonists : Cortagine Corticorelin Corticotropin releasing hormone Sauvagine Stressin I Urocortin Antagonists : Antalarmin Astressin - B CP - 154,526 Emicerfont Hypericin LWH - 234 NBI - 27914 Pexacerfont R - 121919 TS - 041 Verucerfont CRF Agonists : Corticorelin Corticotropin releasing hormone Sauvagine Urocortin Antagonists : Astressin - B Cytokine See here instead. Endothelin Agonists : Endothelin 1 Endothelin 2 Endothelin 3 IRL - 1620 Antagonists : A-192621 ACT - 132577 Ambrisentan Aprocitentan Atrasentan Avosentan Bosentan BQ - 123 BQ - 788 Clazosentan Darusentan Edonentan Enrasentan Fandosentan Feloprentan Macitentan Nebentan Sitaxentan Sparsentan Tezosentan Zibotentan Galanin GAL Agonists : Galanin Galanin ( 1 - 15 ) Galanin - like peptide Galmic Galnon NAX 810 - 2 Antagonists : C7 Dithiepine - 1, 1, 4, 4 - tetroxide Galantide ( M15 ) M32 M35 M40 SCH - 202596 GAL Agonists : Galanin Galanin ( 1 - 15 ) Galanin ( 2 - 11 ) Galanin - like peptide Galmic Galnon J18 NAX 810 - 2 Antagonists : C7 Galantide ( M15 ) M32 M35 M40 M871 GAL Agonists : Galanin Galanin ( 1 - 15 ) Galmic Galnon Antagonists : C7 Galantide ( M15 ) GalR3ant HT - 2157 M32 M35 M40 SNAP - 37889 SNAP - 398299 Ghrelin / GHS See here instead. GH See here instead. GHRH See here instead. GLP GLP - 1 Agonists : Albiglutide Beinaglutide Dulaglutide Efpeglenatide Exenatide GLP - 1 Langlenatide Liraglutide Lixisenatide Oxyntomodulin Semaglutide Taspoglutide GLP - 2 Agonists : Elsiglutide Glepaglutide GLP - 2 Teduglutide Others Propeptides : Preproglucagon Proglucagon Glucagon Agonists : Dasiglucagon Glucagon Oxyntomodulin Antagonists : Adomeglivant L - 168,049 LGD - 6972 Propeptides : Preproglucagon Proglucagon GnRH Agonists : Peptide : Avorelin Buserelin ( buserelin acetate ) Deslorelin Fertirelin ( fertirelin acetate ) Gonadorelin GnRH ( LHRH, gonadorelin ) Goserelin ( goserelin acetate ) Histrelin Leuprorelin ( leuprolide acetate ) Lutrelin Nafarelin Peforelin Triptorelin Zoptarelin doxorubicin Antagonists : Peptide : Abarelix Acyline Cetrorelix Degarelix Detirelix Ganirelix Iturelix Ozarelix Prazarelix Ramorelix Teverelix ( antarelix ) ; Non-peptide : ASP - 1707 Elagolix KLH - 2109 ( OBE - 2109 ) Relugolix Sufugolix Gonadotropin LH / CG Agonists : Choriogonadotropin alfa Human chorionic gonadotropin Luteinizing hormone Lutropin alfa Menotropin ( human menopausal gonadotropin ) FSH Agonists : Corifollitropin alfa Follicle - stimulating hormone Follitropin alfa Follitropin beta Follitropin epsilon Menotropin ( human menopausal gonadotropin ) Urofollitropin Varfollitropin alfa NAMs : ADX - 61623 Growth factor See here instead. Insulin Agonists : Chaetochromin ( 4548 - G05 ) Insulin - like growth factor 1 Insulin - like growth factor 2 Insulin Insulin aspart Insulin degludec Insulin detemir Insulin glargine Insulin glulisine Insulin lispro Mecasermin Mecasermin rinfabate Antagonists : BMS - 754807 S661 S961 Kinase inhibitors : Linsitinib Antibodies : Xentuzumab ( against IGF - 1 and IGF - 2 ) Kisspeptin Agonists : Kisspeptin Kisspeptin - 10 Antagonists : Kisspeptin - 234 Leptin Agonists : Leptin Metreleptin MCH MCH Agonists : Melanin concentrating hormone Antagonists : ATC - 0065 ATC - 0175 GW - 803430 NGD - 4715 SNAP - 7941 SNAP - 94847 MCH Agonists : Melanin concentrating hormone Melanocortin See here instead. Neuropeptide FF Agonists : Neuropeptide AF Neuropeptide FF Neuropeptide SF ( RFRP - 1 ) Neuropeptide VF ( RFRP - 3 ) Antagonists : BIBP - 3226 RF9 Neuropeptide S Agonists : Neuropeptide S Antagonists : ML - 154 SHA - 68 Neuropeptide Y Y Agonists : Neuropeptide Y Peptide YY Antagonists : BIBO - 3304 BIBP - 3226 BVD - 10 GR - 231118 PD - 160170 Y Agonists : 2 - Thiouridine 5 ' - triphosphate Neuropeptide Y Neuropeptide Y ( 13 - 36 ) Peptide YY Peptide YY ( 3 - 36 ) Antagonists : BIIE - 0246 JNJ - 5207787 SF - 11 Y Agonists : GR - 231118 Neuropeptide Y Pancreatic polypeptide Peptide YY Antagonists : UR - AK49 Y Agonists : BWX - 46 Neuropeptide Y Peptide YY Antagonists : CGP - 71683 FMS - 586 L - 152,804 Lu AA - 33810 MK - 0557 NTNCB Velneperit ( S - 2367 ) Neurotensin NTS Agonists : Neurotensin Neuromedin N Antagonists : Meclinertant SR - 142948 NTS Agonists : Neurotensin Antagonists : Levocabastine SR - 142948 Opioid See here instead. Orexin OX Agonists : Orexin ( A, B) Antagonists : ACT - 335827 ACT - 462206 Almorexant Filorexant Lemborexant SB - 334867 SB - 408124 SB - 649868 Suvorexant TCS - 1102 OX Agonists : Orexin ( A, B) SB - 668875 Antagonists : ACT - 335827 ACT - 462206 Almorexant EMPA Filorexant JNJ - 10397049 Lemborexant MK - 1064 SB - 649868 Seltorexant Suvorexant TCS - 1102 TCS - OX2 - 29 Oxytocin See here instead. Prolactin Agonists : Growth hormone Human placental lactogen Placental growth hormone ( growth hormone variant ) Prolactin S179D - hPRL Somatotropin Antagonists : Δ1 -- 9 - G129R - hPRL Δ1 -- 14 - G129R - hPRL G120K - hGH G129R - hPRL Prolactin modulators : Prolactin inhibitors : D receptor agonists ( e.g., bromocriptine, cabergoline ) ; Prolactin releasers : D receptor antagonists ( e.g., domperidone, metoclopramide, risperidone ) Estrogens ( e.g., estradiol ) Progestogens ( e.g., progesterone ) PTH Agonists : Abaloparatide Parathyroid hormone Parathyroid hormone - related protein ( PTHrP ) Semparatide Teriparatide Relaxin Agonists : Insulin - like factor 3 Relaxin ( 1, 2, 3 ) Serelaxin Somatostatin See here instead. Tachykinin See here instead. TRH Agonists : Azetirelin Fertirelin Montirelin Orotirelin Posatirelin Protirelin Rovatirelin Taltirelin TRH ( TRF ) TSH Agonists : Thyrotropin alfa TSH ( thyrotropin ) Vasopressin See here instead. VIP / PACAP VIPR Agonists : Peptide : Bay 55 - 9837 LBT - 3393 PACAP VIP VIPR Agonists : Peptide : LBT - 3627 PACAP VIP PAC Agonists : PACAP PACAP ( 1 - 27 ) PACAP ( 1 - 38 ) Antagonists : PACAP ( 6 - 38 ) Unsorted PHI PHM PHV Others Endogenous : Adrenomedullin Apelin Asprosin Bombesin Calcitonin Carnosine CART CLIP DSIP Enteroglucagon Formyl peptide GALP GIP GRP Integrin ligands ( collagens, fibrinogen, fibronectin, laminins, ICAM - 1, ICAM - 2, osteopontin, VCAM - 1, vitronectin ) Kininogens Motilin Natriuretic peptides ( ANP, BNP, CNP, urodilatin ) Nesfatin - 1 Neuromedin B Neuromedin N Neuromedin S Neuromedin U Obestatin Osteocalcin Resistin Secretin Thymopoietin Thymosins Thymulin Urotensin - II VGF Exogenous : Lifitegrast ( LFA - 1 antagonist ) See also Receptor / signaling modulators NDL : 00569089 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Peptide&oldid=804978488 '' Categories : Peptides Hidden categories : CS1 maint : Multiple names : authors list CS1 maint : Explicit use of et al. 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Question: a long chain of amino acids linked by peptide bonds is a
Answer: polypeptide