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Peptide research glossary

69 plain-English definitions of the terms used across the compound pages. Descriptive only: nothing here is dosing or usage guidance.

A

Acylation: Attaching a fatty-acid chain to a peptide. It promotes binding to serum albumin and slows clearance, which is how several long-acting GLP-1 analogues are built.See: Liraglutide, Semaglutide
Aggregation: The clumping together of peptide molecules into insoluble assemblies. It is why native human amylin cannot be used directly, and why analogues such as pramlintide were engineered.See: Pramlintide
Agonist: A molecule that binds a receptor and activates it, mimicking the natural signal. Semaglutide, for example, is a GLP-1 receptor agonist.See: Semaglutide
Albumin binding: Reversible attachment of a modified peptide to serum albumin. Fatty-acid side chains promote it, shielding the peptide from clearance and lengthening its half-life.See: Semaglutide, Liraglutide
Alpha-helix: A common coiled secondary structure in peptides, stabilised by hydrogen bonds along the backbone. Many receptor-binding peptides adopt a helix when they bind.
Amidation (C-terminal): Replacing the carboxyl end of a peptide with an amide group. It removes a negative charge, often improves stability and is common in naturally occurring hormones.
Amino acid: The building block of peptides and proteins. Twenty standard amino acids are encoded by DNA; research peptides sometimes include unnatural or D-form residues.
Analogue: A compound built by modifying a natural peptide, for instance by swapping residues or adding a fatty-acid chain, to change stability or receptor behaviour.
Antagonist: A molecule that binds a receptor without activating it, blocking the natural signal.

B

Batch number: An identifier linking a vial to one manufacturing run and its analytical records, so a Certificate of Analysis can be matched to the material in hand.
Bioavailability: The fraction of a substance that reaches the circulation in active form. Peptides generally have low oral bioavailability because digestive enzymes break them down.

C

Certificate of Analysis (CoA): A document reporting the tests run on a batch, typically HPLC purity and mass spectrometry identity. It is only meaningful if it matches your batch reference.
Chromatogram: The trace produced by HPLC, with peaks for each component of a sample. Purity is calculated from the area of the main peak relative to the total.
Counter-ion: A small ion, such as acetate or trifluoroacetate, that balances the charge on a peptide. It contributes to vial weight but is not peptide.
Cyclic peptide: A peptide whose ends or side chains are joined into a ring, for example through a disulfide bond. Ring closure can improve stability and receptor selectivity.See: Oxytocin

D

D-amino acid: The mirror-image form of an amino acid. Inserting D-residues into a peptide makes it harder for enzymes to cut, as seen in hexarelin and several other secretagogues.See: Hexarelin, GHRP-2
Desensitisation: A fading response of a receptor after repeated or continuous activation. Ghrelin-receptor agonists such as hexarelin are a well-documented example.See: Hexarelin
Disulfide bond: A covalent link between the sulfur atoms of two cysteine residues. It can close a ring within one peptide or join two chains.
DPP-4: Dipeptidyl peptidase-4, an enzyme that rapidly cleaves native GLP-1 and some other peptides. Resistance to it is a major design goal for GLP-1 analogues.See: Exenatide
Dual agonist: A compound designed to activate two receptors at once, such as GIP and GLP-1.See: Tirzepatide

E

Endogenous: Produced naturally inside the body, as opposed to a synthetic or administered compound.
Endotoxin: A fragment of bacterial cell wall that can contaminate preparations. Endotoxin testing is a standard quality check for peptides used in cell-based work.
Evidence level: peptide.wiki's one-to-five rating of the published literature for a compound, from approved medicine with phase 3 trials (5) to limited preclinical data (1). See the methodology page.
Excipient: An inactive ingredient in a lyophilised product, such as a bulking agent, that helps the freeze-dried cake form and stay stable.

G

Gastric emptying: The rate at which the stomach releases food into the intestine. Slowing it is one of the actions of GLP-1 and amylin receptor agonists.
Ghrelin: A gut-derived hormone that activates the GHS receptor, driving growth hormone release and appetite signalling.See: Ipamorelin, GHRP-6
GHRH: Growth-hormone-releasing hormone, a 44-residue hypothalamic peptide that prompts the pituitary to release growth hormone. Sermorelin and CJC-1295 are GHRH analogues.See: Sermorelin, CJC-1295
GHS-R (ghrelin receptor): The receptor that growth hormone secretagogues such as ipamorelin and GHRP-6 act on.See: Ipamorelin, GHRP-6, GHRP-2
GIP: Glucose-dependent insulinotropic polypeptide, an incretin hormone. Dual agonists such as tirzepatide activate both its receptor and the GLP-1 receptor.See: Tirzepatide
GLP-1: Glucagon-like peptide-1, an incretin hormone released from the gut. A family of long-acting analogues targets its receptor.See: Semaglutide, Liraglutide
Glucagon: A pancreatic hormone that raises blood glucose and increases energy expenditure. Triple agonists such as retatrutide add activity at its receptor.See: Retatrutide
Glucagon receptor (GCGR): The receptor activated by the hormone glucagon. Dual agonists such as survodutide and mazdutide combine GLP-1 receptor activity with glucagon-receptor activity.See: Survodutide, Mazdutide
Gonadotropin-releasing hormone (GnRH): A ten-amino-acid hypothalamic hormone that signals the pituitary to release LH and FSH. Gonadorelin is its synthetic copy.See: Gonadorelin

H

Half-life: The time for the concentration of a substance to fall by half. Chemical modifications are often made specifically to lengthen a peptide's half-life.
HPLC: High-performance liquid chromatography. It separates the components of a sample, and the purity on a CoA is the share of the main peak in the chromatogram.

I

IGF-1: Insulin-like growth factor 1, produced mainly by the liver in response to growth hormone. It is the main downstream mediator of GH signalling and a common readout in GH-axis research.See: IGF-1 LR3
In vitro: Done in a dish or test tube rather than in a living organism. Research peptides on this site are described for in vitro laboratory research only.
Incretin: A gut hormone, such as GLP-1 or GIP, that influences insulin secretion and appetite signalling.
Innate repair receptor: A receptor complex of the erythropoietin receptor and the common beta receptor, associated with tissue-protective rather than blood-cell signalling. ARA 290 was designed to target it.See: ARA 290
Isoelectric point (pI): The pH at which a peptide carries no net charge. It affects solubility and how the peptide behaves in chromatography.

L

Lipolysis: The breakdown of stored fat into free fatty acids and glycerol.
Lyophilised: Freeze-dried. Most research peptides are supplied as a lyophilised powder because the dry form is far more stable than a solution.

M

m/z: Mass-to-charge ratio, the quantity a mass spectrometer actually measures. A multiply charged peptide shows several m/z peaks from which its mass is calculated.
Mass spectrometry (MS): A technique that measures molecular mass. It confirms a peptide's identity by comparing the observed mass with the theoretical mass.
Melanocortin receptors: A family of five receptors (MC1R to MC5R) involved in pigmentation, appetite and other processes. MC4R and MC1R are the best known.See: Melanotan II, Setmelanotide
Mitochondrial-derived peptide (MDP): A short peptide encoded within mitochondrial DNA rather than the nuclear genome. Humanin and MOTS-c are the best-known examples.See: Humanin, MOTS-c
Molar concentration: Moles of a substance per litre. Converting a mg/mL stock to molar needs the molecular weight; see the stock solution calculator.
Molecular weight: The mass of one mole of a molecule, in g/mol or daltons. It is needed to convert between mass and molar concentrations.
Monoisotopic mass: Mass calculated using the most abundant isotope of each element. It matches the main peak in high-resolution mass spectrometry.

N

N-terminus / C-terminus: The two ends of a peptide chain: the free amino end and the free carboxyl end. Modifications there, such as acetylation or amidation, change stability and charge.
Net peptide content: The proportion of a lyophilised vial that is actual peptide, the rest being counter-ions and water. It is usually lower than HPLC purity.

O

Off-label: Use of an approved medicine outside its authorised indication. It is a regulatory term for medicines and says nothing about research compounds.
Oxyntomodulin: A natural gut hormone that activates both the GLP-1 and glucagon receptors. Several dual agonists are analogues of it.See: Mazdutide

P

Peptide: A short chain of amino acids joined by peptide bonds. By convention, chains longer than roughly 50 residues are called proteins.
Peptide bond: The amide bond joining the carboxyl group of one amino acid to the amino group of the next.
Pharmacokinetics: How a compound is absorbed, distributed, broken down and cleared over time. Half-life is its most quoted parameter.
Preclinical: Research in cells or animals before any human trials. Most data for newer research peptides sits at this stage.
PTH1 receptor: The receptor activated by parathyroid hormone and by its active fragment teriparatide.See: Teriparatide
Purity: On a CoA, usually the percentage of the main peak by HPLC. It describes related peptide impurities, not water or salt content.

R

Receptor: A protein, usually on a cell surface, that a signalling molecule binds to in order to trigger a cellular response.
Receptor selectivity: How strongly a compound prefers one receptor over related ones. High selectivity makes a cleaner research tool; low selectivity brings broader effects.See: Ipamorelin
Reconstitution: Dissolving a lyophilised powder in a solvent to make a solution. See the stock solution calculator for the concentration arithmetic.
Residue: A single amino acid unit within a peptide chain.

S

Secretagogue: A substance that prompts the secretion of another, such as growth hormone secretagogues that prompt pituitary release.See: CJC-1295, Ipamorelin
Sequence: The ordered list of amino acids in a peptide, written from the N-terminus to the C-terminus using one- or three-letter codes.
Solid-phase peptide synthesis (SPPS): The standard way to make research peptides: amino acids are added one at a time to a chain anchored on a resin, then the finished peptide is cleaved off and purified.

T

Trifluoroacetate (TFA) salt: A common counter-ion left over from peptide purification. It adds mass to the vial, which is why net peptide content is lower than total weight.
Tripeptide: A peptide of exactly three amino acids, such as GHK, the core of GHK-Cu.See: GHK-Cu
Truncation: Using only part of a natural peptide's sequence. Sermorelin is a truncation of GHRH that keeps full activity in 29 of its 44 residues.See: Sermorelin

For laboratory research only. Nothing on peptide.wiki is medical advice. The compounds described are not for human or veterinary use, and research-grade material is not a medicine.