Peptide Research Glossary
A comprehensive A–Z reference of peptide and research compound terminology. Covering synthesis, testing, pharmacology, and laboratory practice.
A
4 termsAmino Acid
The fundamental building blocks of peptides and proteins. There are 20 standard amino acids, each with a unique side chain that determines its chemical properties. Peptides are formed when amino acids are joined together via peptide bonds. The sequence, length, and composition of amino acids define a peptide's biological activity.
Analogue
A synthetic compound that is structurally similar to a naturally occurring molecule but has been chemically modified to alter its stability, potency, or receptor affinity. Many research peptides are analogues of endogenous hormones or signalling molecules, engineered for improved half-life or targeted activity.
Agonist
A molecule that binds to a receptor and activates it, producing a biological response. An agonist mimics the action of the naturally occurring ligand at that receptor. Many research peptides function as agonists at growth hormone, melanocortin, or opioid receptors.
B
3 termsBacteriostatic Water (BAC Water)
Sterile water containing 0.9% benzyl alcohol, used as a solvent for reconstituting lyophilised peptides. The benzyl alcohol acts as a preservative, inhibiting bacterial growth and allowing a reconstituted solution to be stored for up to 28 days when refrigerated. It is the standard diluent used in peptide research.
Bioavailability
The proportion of a compound that enters systemic circulation and is able to exert a biological effect. A compound administered intravenously has 100% bioavailability. Subcutaneous and intramuscular administration typically achieve high bioavailability for peptides, while oral bioavailability is generally very low due to enzymatic degradation in the gastrointestinal tract.
Binding Affinity
The strength of the interaction between a molecule (such as a peptide) and its target receptor. Higher binding affinity means the molecule binds more tightly, often resulting in a greater biological effect at lower concentrations. Measured as Kd (dissociation constant). A lower Kd indicates higher affinity.
C
3 termsCAS Number
A unique numerical identifier assigned by the Chemical Abstracts Service (CAS) to every chemical substance, including peptides, small molecules, and compounds. CAS numbers allow unambiguous identification of a compound regardless of its trade name or synonym. For example, BPC-157 has CAS number 137525-51-0.
Certificate of Analysis (COA)
A document provided by a laboratory confirming that a batch of compound meets specified quality standards. A COA for a research peptide typically includes the compound name, batch number, molecular weight, purity percentage (from HPLC analysis), mass spectrometry confirmation, and the date of testing. Third-party COAs from independent laboratories provide the highest level of quality assurance.
cGMP (Current Good Manufacturing Practice)
A set of regulations and guidelines enforced by regulatory bodies (such as the MHRA in the UK and FDA in the US) that govern the manufacture, testing, and quality control of pharmaceutical-grade compounds. cGMP-compliant synthesis ensures consistent purity, potency, and safety across production batches.
D
2 termsDisulfide Bond
A covalent bond formed between two cysteine residues within a peptide or protein. Disulfide bonds play a critical role in stabilising the three-dimensional structure of many peptides and proteins, and can influence receptor binding and biological activity.
Dose-Response Relationship
The relationship between the concentration or dose of a compound and the magnitude of a biological response. In research settings, characterising the dose-response curve helps determine the effective concentration (EC50) and maximum effect (Emax) of a peptide.
E
3 termsEC50
The concentration of a compound that produces 50% of its maximum possible effect. EC50 is a standard measure of potency. A lower EC50 indicates a more potent compound, requiring a smaller concentration to achieve the half-maximal response.
Endogenous
Produced or originating from within an organism. Endogenous peptides are those naturally synthesised by the body, such as growth hormone-releasing hormone (GHRH) or oxytocin. Many research peptides are analogues of endogenous compounds.
Exogenous
Originating from outside an organism. An exogenous peptide is one that is introduced into a biological system from an external source, as opposed to being produced by the organism itself.
G
2 termsGrowth Hormone Secretagogue (GHS)
A class of compounds that stimulate the release of growth hormone (GH) from the pituitary gland. GHS peptides work primarily by mimicking ghrelin and binding to the GHS-R1a receptor. Examples include GHRP-2, GHRP-6, Ipamorelin, and Hexarelin.
GHRH (Growth Hormone-Releasing Hormone)
An endogenous hypothalamic hormone that stimulates the pituitary gland to produce and release growth hormone. GHRH analogues used in research, such as Sermorelin, CJC-1295, and Tesamorelin, act on the GHRH receptor to promote natural GH secretion patterns.
H
2 termsHalf-Life
The time it takes for the concentration of a compound in a biological system to reduce by 50%. Peptides typically have short half-lives due to rapid enzymatic degradation. Chemical modifications such as PEGylation or the addition of a DAC (Drug Affinity Complex) can significantly extend a peptide's half-life, as seen with PEG-MGF and CJC-1295 with DAC.
HPLC (High-Performance Liquid Chromatography)
An analytical technique used to separate, identify, and quantify components in a compound mixture. In peptide quality testing, HPLC is the gold standard method for determining purity. A compound is passed through a column under high pressure; components separate based on their interactions with the stationary phase, and the resulting chromatogram shows the proportion of each component. A purity of ≥98% by HPLC is considered research-grade.
I
4 termsIGF-1 (Insulin-Like Growth Factor 1)
A peptide hormone structurally similar to insulin, primarily produced in the liver in response to growth hormone stimulation. IGF-1 mediates many of the anabolic effects of growth hormone and plays a key role in cell growth, proliferation, and survival. IGF-1 LR3 is a long-acting research analogue with an extended half-life.
Intramuscular (IM)
A route of administration in which a compound is injected directly into muscle tissue. Intramuscular injection is commonly used in research for compounds requiring reliable absorption. It generally results in slightly slower absorption than intravenous but faster than subcutaneous administration.
In Vitro
Latin for 'in glass', referring to experiments conducted outside of a living organism, typically in a controlled laboratory environment such as in a test tube, cell culture dish, or other artificial setting. In vitro studies are often the first step in characterising a compound's biological activity.
In Vivo
Latin for 'within the living', referring to experiments conducted within a living organism. In vivo studies assess how a compound behaves in the complex biological environment of a whole organism, including absorption, distribution, metabolism, and excretion (ADME).
K
1 termsKd (Dissociation Constant)
A measure of the tendency of a complex (such as a peptide-receptor complex) to dissociate. A lower Kd value indicates a higher binding affinity, meaning the compound stays bound to its receptor longer. Kd is commonly used to compare the potency of different compounds at the same receptor.
L
2 termsLigand
Any molecule that binds to a specific receptor to form a complex. In the context of peptide research, a ligand is typically a peptide or small molecule that binds to a biological receptor and either activates (agonist) or blocks (antagonist) it.
Lyophilisation (Freeze-Drying)
A preservation process in which a compound is first frozen, then subjected to a high vacuum that causes the frozen water to sublimate (convert directly from ice to vapour), leaving behind a dry, stable powder. Lyophilised peptides have significantly longer shelf lives than solutions and are more stable during shipping and storage. They must be reconstituted with an appropriate solvent before use.
M
4 termsMass Spectrometry (MS)
An analytical technique that measures the mass-to-charge ratio of ions to identify and confirm the molecular structure of a compound. In peptide QC, mass spectrometry is used alongside HPLC to confirm that the compound has the correct molecular weight, verifying its identity. MS-UPLC (Ultra-Performance Liquid Chromatography coupled with mass spectrometry) is a particularly sensitive variant.
Melanocortin Receptor
A family of G protein-coupled receptors (MC1R–MC5R) that respond to melanocortin peptides including alpha-MSH and ACTH. Several research peptides, including PT-141 (Bremelanotide), target melanocortin receptors, particularly MC3R and MC4R, and are studied for their effects on various physiological systems.
Molecular Formula
A representation of the types and numbers of atoms present in a molecule. For peptides, the molecular formula reflects the amino acid composition. For example, BPC-157 has the molecular formula C62H98N16O22. The molecular formula is used alongside molecular weight to confirm compound identity.
Molecular Weight (MW)
The sum of the atomic weights of all atoms in a molecule, typically expressed in Daltons (Da) or grams per mole (g/mol). Molecular weight is a key identifier for peptides and is used to confirm compound identity via mass spectrometry. Smaller peptides (<1,000 Da) are often called 'small peptides', while larger ones (>10,000 Da) approach protein size.
N
1 termsN-terminus / C-terminus
The two ends of a peptide chain. The N-terminus is the end with a free amino group (–NH2), and the C-terminus is the end with a free carboxyl group (–COOH). Peptide sequences are conventionally written from N-terminus to C-terminus. Chemical modifications at these termini are commonly used to improve peptide stability and half-life.
P
5 termsPEGylation
The process of attaching polyethylene glycol (PEG) chains to a peptide molecule. PEGylation increases the hydrodynamic size of the peptide, which slows kidney filtration and reduces enzymatic degradation, dramatically extending the compound's half-life. PEG-MGF is an example of a PEGylated research peptide.
Peptide
A short chain of amino acids linked by peptide bonds. Peptides are typically defined as containing fewer than 50 amino acids (longer chains are called proteins). Peptides act as biological signalling molecules, hormones, neurotransmitters, and structural components. Research peptides are synthesised versions of these naturally occurring molecules used in scientific study.
Peptide Bond
The covalent chemical bond formed between the carboxyl group (–COOH) of one amino acid and the amino group (–NH2) of another, with the release of a water molecule. This bond is the fundamental link in a peptide chain. Peptide bonds are planar and relatively rigid, contributing to the secondary structure of peptides.
Pulsatile Release
The natural pattern of hormone secretion in which bursts (pulses) of hormone are released at intervals rather than continuously. Growth hormone, for example, is released in pulses, primarily overnight. Research peptides that stimulate natural GH secretion aim to preserve or mimic this pulsatile pattern, which is physiologically important.
Purity
The proportion of the compound of interest relative to all other substances in a sample, typically expressed as a percentage. Purity is most commonly measured by HPLC. Research-grade peptides should have a minimum purity of ≥98% (HPLC). Lower purity indicates the presence of impurities, synthesis by-products, or degradation products that could confound research results.
R
2 termsReceptor
A protein molecule, typically located on the surface of or within a cell, that receives and responds to specific chemical signals (ligands). When a peptide binds to its target receptor, it triggers a cascade of intracellular events that produce a biological response. Receptor specificity determines which cells and tissues a peptide can affect.
Reconstitution
The process of dissolving a lyophilised (freeze-dried) peptide powder in an appropriate solvent, typically bacteriostatic water, to create a solution for use in research. Proper reconstitution technique involves injecting the solvent gently down the side of the vial to avoid denaturing the peptide, then swirling rather than shaking to mix.
S
4 termsSequence
The specific order of amino acids in a peptide chain, written from N-terminus to C-terminus using one-letter or three-letter amino acid codes. The sequence entirely determines the peptide's three-dimensional structure and biological activity. For example, the sequence of BPC-157 is Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val.
SKU (Stock Keeping Unit)
A unique alphanumeric identifier assigned to each distinct product or variant in inventory. In the context of research peptides, each vial size or formulation of a compound typically has its own SKU to allow precise tracking and ordering.
Solid-Phase Peptide Synthesis (SPPS)
The dominant method for synthesising research peptides. Amino acids are added sequentially to a growing chain that is anchored to a solid resin support, then cleaved and purified at the end. SPPS allows precise control over peptide sequence and enables the production of peptides that would be difficult or impossible to isolate from natural sources.
Subcutaneous (SC)
A route of administration in which a compound is injected into the subcutaneous tissue, the fatty layer just beneath the skin. Subcutaneous injection is a common route for peptide research due to its ease of administration and reliable absorption. The injection is typically made at a 45-degree angle using a short, fine needle.
T
2 termsTachyphylaxis
Rapid diminishing of a response to a compound following repeated administration, commonly referred to as desensitisation or tolerance. Some GH secretagogue peptides, particularly GHRP-6 and Hexarelin, can produce tachyphylaxis at the pituitary level with continuous use, which is why cyclical research protocols are often studied.
Terminus Modification
A chemical alteration made to the N- or C-terminus of a peptide to improve its properties. Common modifications include amidation of the C-terminus (–NH2 instead of –COOH) and acetylation of the N-terminus, both of which can improve metabolic stability, increase half-life, and alter receptor binding characteristics.
U
1 termsUPLC (Ultra-Performance Liquid Chromatography)
An advanced form of HPLC that uses smaller particle sizes and higher pressures to achieve faster separations with greater sensitivity and resolution. UPLC is increasingly used in peptide quality control, often coupled with mass spectrometry (MS-UPLC) to provide rapid, high-resolution purity and identity confirmation.
V
1 termsVial
A small glass or plastic container used to store research compounds. Lyophilised peptides are typically supplied in sealed glass vials, often with a rubber stopper and aluminium crimp cap that allows a syringe needle to be inserted for reconstitution without fully opening the vial, maintaining sterility.
Ready to explore our compounds?
Browse our full catalogue of research-grade peptides, all HPLC verified with third-party COA.
Browse Compounds