Peptide glossary: names, codes and synonyms

Why does the same peptide have several names?

A research compound can appear under its technical name (INN), its laboratory code during development, or the brand name of the reference drug that shares the same active ingredient. That is why someone searches for "generic Mounjaro" when they mean tirzepatide, or "copper peptide" when looking for GHK-Cu. The equivalences are below.

Scientific glossary: key concepts in peptide research

Each term has its own page with the definition, why it matters in the lab, the compounds involved and the Peptide University lessons that cover it in depth.

Chemistry and structure

• Amino acidAn amino acid is the basic building block of peptides and proteins: a molecule with an amino group, a…
• Amino acid sequenceThe sequence (or primary structure) is the exact order of the amino acids in the chain, read from the…
• C-terminal amidationC-terminal amidation replaces the free carboxyl group at the end of the chain (–COOH) with an amide (–CONH₂).
• CAS numberA CAS number is a unique identifier assigned by the Chemical Abstracts Service to each chemical substance.
• Cyclic peptideA cyclic peptide is one whose chain closes on itself to form a ring, through a bond between its two ends or…
• D-amino acidsD-amino acids are the “mirror” forms of natural (L) amino acids. Building them into a peptide makes it much…
• Disulfide bridgeA disulfide bridge is a covalent bond between the sulphur atoms of two cysteines. It closes rings within a…
• Hydrophobicity and solubilityA peptide's solubility depends on the balance between hydrophobic amino acids (which avoid water) and…
• Isoelectric point (pI)The isoelectric point (pI) is the pH at which a peptide carries zero net electrical charge.
• Lipidation (fatty-acid acylation)Lipidation attaches a fatty-acid chain to a peptide. The peptide then binds to albumin in the blood and its…
• Molecular weightMolecular weight is the mass of a molecule, expressed in daltons (Da) or g/mol. For a peptide it is…
• N-terminal acetylationN-terminal acetylation adds an acetyl group (CH₃CO–) to the free amino group at the start of the chain.
• Non-natural amino acidsThey are amino acids that are not among the 20 the body uses to build proteins. They are built into…
• PEGylationPEGylation attaches polyethylene glycol (PEG) chains to a peptide or protein to increase its apparent size…
• PeptideA peptide is a short chain of amino acids joined by peptide bonds. By convention, chains of up to about 50…
• Peptide analogueAn analogue is a modified version of a natural peptide that keeps its activity at the same receptor but…
• Peptide bondThe peptide bond is the amide link formed between the carboxyl group of one amino acid and the amino group…
• Secondary structureSecondary structure refers to the local folding patterns of the chain, mainly alpha helices and beta sheets…
• Solid-phase peptide synthesis (SPPS)Solid-phase synthesis builds a peptide one amino acid at a time on an insoluble resin. It is the method used…

Pharmacology

• Affinity and potency (EC50)Affinity measures how strongly a molecule binds to its receptor; potency, what concentration it needs to…
• AgonistAn agonist is a molecule that binds to a receptor and activates it, mimicking the action of that receptor's…
• Albumin binding and DACSome peptides are designed to bind to blood albumin, which shields them and releases them gradually.
• AntagonistAn antagonist is a molecule that binds to a receptor without activating it and, by occupying it, prevents…
• Biased agonismBiased agonism occurs when an agonist preferentially activates some of a receptor's signalling pathways over…
• BioavailabilityBioavailability is the fraction of an administered substance that reaches the systemic circulation intact.
• Cmax, Tmax and AUCThey are the basic parameters of a blood concentration curve: Cmax is the peak concentration, Tmax the time…
• DPP-4 (dipeptidyl peptidase-4)DPP-4 is an enzyme that cuts off the first two amino acids of certain peptides. It is the main reason…
• Dual and triple agonistA dual agonist is a single molecule able to activate two different receptors; a triple agonist, three.
• G protein-coupled receptor (GPCR)GPCRs are the largest family of membrane receptors. They detect a signal outside the cell and relay it…
• Growth hormone secretagogueA secretagogue is a substance that stimulates the release of another. GH secretagogues make the pituitary…
• Half-lifeHalf-life (t½) is the time it takes for the concentration of a substance in the body or in a solution to…
• ImmunogenicityImmunogenicity is the ability of a substance to trigger an immune system response, such as the formation of…
• Incretin effectThe incretin effect is the observation that glucose taken by mouth triggers a much larger insulin release…
• PharmacodynamicsPharmacodynamics studies what a substance does to the body: which target it acts on, how it activates or…
• PharmacokineticsPharmacokinetics studies what the body does to a substance: how it is absorbed, distributed, metabolised and…
• ProteasesProteases (or peptidases) are enzymes that cut peptide bonds. They are the main route by which the body…
• Renal clearanceRenal clearance is the removal of a substance from the blood by the kidneys. Small peptides are filtered…
• Subcutaneous routeThe subcutaneous route places the substance in the fatty tissue under the skin, from where it passes slowly…
• Tachyphylaxis and desensitisationTachyphylaxis is the rapid loss of response to repeated or continuous exposure to a substance.

Hormones, receptors and systems

• AMPKAMPK (AMP-activated protein kinase) is the cell's energy sensor. It is activated when energy runs low and…
• AmylinAmylin is a peptide hormone the pancreas releases together with insulin. It slows gastric emptying, reduces…
• AngiogenesisAngiogenesis is the formation of new blood vessels from existing ones. It is an essential step in wound…
• Antimicrobial peptidesAntimicrobial peptides are innate immunity molecules that damage the membrane of bacteria, fungi or viruses…
• BDNFBDNF (brain-derived neurotrophic factor) is a protein that supports neuron survival, the growth of their…
• CardiolipinCardiolipin is a phospholipid found almost exclusively in the inner mitochondrial membrane, essential for…
• Cellular senescenceSenescence is a state in which a cell permanently stops dividing but stays alive and active, releasing…
• GhrelinGhrelin is a hormone produced mainly by the stomach. It stimulates appetite and, through its GHS-R1a…
• GHRHGHRH (growth hormone-releasing hormone) is the hypothalamic peptide that tells the pituitary to produce and…
• GIPGIP (glucose-dependent insulinotropic polypeptide) is the other major incretin: a hormone from the duodenum…
• GLP-1GLP-1 (glucagon-like peptide-1) is a gut hormone that amplifies glucose-dependent insulin secretion, slows…
• Glucagon receptorGlucagon is the pancreatic hormone that raises glucose during fasting. Activating its receptor together with…
• Hypothalamic-pituitary-gonadal axisIt is the hormonal system that regulates reproduction: the hypothalamus releases GnRH, the pituitary…
• IGF-1IGF-1 (insulin-like growth factor 1) is the main mediator of growth hormone's effects. It is produced mostly…
• Insulin resistanceInsulin resistance is a reduced response of muscle, liver and fat tissue to insulin, which forces the…
• MASLD and MASH (metabolic fatty liver)MASLD is fat build-up in the liver associated with metabolic dysfunction; MASH is its inflammatory form…
• Melanocortin systemMelanocortins are POMC-derived peptides, such as α-MSH, that act on five receptors (MC1R to MC5R) involved…
• Mitochondrial-derived peptidesThey are peptides encoded in the mitochondrion's own DNA, such as MOTS-c or humanin, that act as signals…
• NF-κBNF-κB is a transcription factor that acts as a central switch of inflammation: when activated, it turns on…
• Oxidative stressOxidative stress is the imbalance between the production of reactive oxygen species and the cell's ability…
• SirtuinsSirtuins are a family of enzymes that regulate the activity of other proteins by removing acetyl groups from…
• SomatostatinSomatostatin is a peptide hormone that holds back the release of other hormones, including growth hormone.
• Telomeres and telomeraseTelomeres are repeated sequences that protect the ends of chromosomes and shorten with every cell division.

Analytical quality

• Amino acid analysisAmino acid analysis breaks the peptide down into its amino acids and quantifies them. It is used to confirm…
• Batch and traceabilityA batch is the quantity of product made in a single process under the same conditions. Its number links each…
• Certificate of analysis (COA)A certificate of analysis is the document that reports the test results of a specific batch: identity…
• Counter-ion (TFA and acetate)The counter-ion is the oppositely charged molecule that accompanies a peptide in salt form.
• EndotoxinsEndotoxins are fragments of the wall of Gram-negative bacteria (lipopolysaccharides) that trigger a strong…
• Freeze-drying (lyophilisation)Freeze-drying (lyophilisation) freezes the peptide solution and removes the water by sublimation under…
• HPLCHPLC (high-performance liquid chromatography) separates the components of a sample and makes it possible to…
• Independent laboratory testingIndependent testing is carried out by a laboratory unrelated to the manufacturer and the seller.
• Mass spectrometryMass spectrometry measures the mass of molecules very precisely. For peptides it is used to confirm…
• Peptide contentPeptide content is the percentage of the freeze-dried powder that is actually peptide. The rest is residual…
• Peptide purityPurity shows what proportion of the peptide material corresponds to the correct sequence. It is expressed as…
• Related impuritiesRelated impurities are molecules very similar to the correct peptide (one amino acid short, truncated…
• Residual moistureResidual moisture is the water left in the powder after freeze-drying. The lower it is, the more stable the…
• Sterility testA sterility test checks that a sample contains no viable microorganisms by incubating it in culture media…

Laboratory handling

• AggregationAggregation is peptide molecules sticking to each other, forming anything from small invisible complexes to…
• AliquotsAn aliquot is a measured portion of a solution. Dividing a reconstituted peptide into single-use aliquots…
• Aseptic techniqueAseptic technique is the set of practices that prevent microorganisms from being introduced into sterile…
• Benzyl alcoholBenzyl alcohol is the preservative in bacteriostatic water. At a 0.9% concentration it inhibits bacterial…
• Cold chainThe cold chain is keeping a product within a temperature range throughout its journey, from manufacture to…
• Concentration (mg/mL)Concentration is the amount of peptide per unit of volume. It is calculated by dividing the vial's mass by…
• DeamidationDeamidation is a degradation reaction in which asparagine (or glutamine) loses its amide group and becomes…
• Peptide oxidationOxidation modifies sensitive amino acids (mainly methionine, cysteine, tryptophan and histidine) through…
• pH and bufferspH determines a peptide's charge, its solubility and the rate of many degradation reactions.
• ReconstitutionReconstituting means dissolving the freeze-dried peptide in a known volume of a suitable solvent to obtain a…
• Stability in solutionOnce dissolved, a peptide starts to degrade through reactions that need water. Its stability in solution…
• Sterile filtrationPeptides cannot withstand autoclave heat, so their solutions are sterilised by filtration through…
• Sterile water for injectionSterile water for injection is purified, sterile water with no preservatives, intended for single use.
• U-100 syringe and unitsOn a U-100 syringe, 100 units equal 1 mL. Each marked unit therefore corresponds to 0.01 mL: it is a volume…

Evidence and regulation

• Animal modelAn animal model is a laboratory species in which a condition is reproduced or an effect is studied, to…
• Clinical trial phasesClinical development of a substance is divided into phases: phase 1 studies safety in a few people, phase 2…
• Clinical trial registryA clinical trial registry is a public database where studies are listed before they start, with their design…
• COFEPRISCOFEPRIS (Federal Commission for the Protection against Sanitary Risks) is Mexico's health authority, which…
• Double-blind and placeboDouble-blind means that neither the participants nor the researchers assessing them know who receives the…
• EMA (European Medicines Agency)The EMA is the European Union agency that evaluates medicines for authorisation in member states.
• FDA and compounding (503A)The FDA is the United States health authority. Its list of bulk substances for compounding (503A) includes a…
• Meta-analysis and systematic reviewA meta-analysis statistically combines the results of several studies on the same question to obtain a more…
• Observational studyIn an observational study researchers record what happens without assigning any treatment. It can show…
• P-value and statistical significanceThe p-value shows how likely it would be to observe a result as extreme or more if there were actually no…
• Peer reviewPeer review is the process in which other specialists assess a paper before a journal publishes it.
• PharmacovigilancePharmacovigilance is monitoring the safety of medicines once they are used in the population: collecting…
• Preclinical studyA preclinical study is research done before a substance is tested in people: in cell cultures (in vitro) or…
• Publication biasPublication bias is the tendency for studies with positive results to be published more easily than those…
• Randomised controlled trialIt is a study in which participants are randomly assigned to receive the intervention or a control (placebo…
• RUO (research use only)RUO (Research Use Only) means a product is sold exclusively for scientific research. It is not a medicine…
• Sanitary registrationSanitary registration is the authorisation granted by the health authority (in Mexico, COFEPRIS) for a…
• WADA Prohibited ListMany research peptides are included on the World Anti-Doping Agency (WADA) Prohibited List, which is updated…

Frequently asked questions