Peptide Research Glossary
85 terms you'll meet in peptide research, explained in plain English, from HPLC to lyophilisation. Terms with a full entry link to a detailed explanation with sources.
A
- Acetate salt β
- A peptide whose protonated basic groups are paired with acetate ions, usually made by exchanging the trifluoroacetate left from synthesis; many peptide medicines are supplied in this form.
- Agonist β
- A ligand that binds a receptor and stabilises an active state, triggering a cellular response; agonists are compared by potency (EC50) and efficacy (maximal response).
- Aliquot β
- A measured portion taken from a larger stock; in peptide work, one of the single-use volumes a reconstituted solution is divided into before storage.
- Amino acid β
- A molecule carrying an amine group, a carboxylic acid group and a variable side chain; peptides are chains of amino acids linked by peptide bonds.
- Analogue
- A modified version of a natural molecule, engineered for stability, selectivity or potency β semaglutide is a GLP-1 analogue; CJC-1295 a GHRH analogue.
- Assay
- Any standardised laboratory test measuring presence, amount or activity β binding assays, purity assays, cell-viability assays.
B
- Bacteriostatic water β
- Sterile water containing 0.9% benzyl alcohol, a preservative that suppresses bacterial growth so a vial can be punctured and drawn from more than once.
- Batch number
- The identifier tying a specific production run to its testing documents. The batch number on a vial label should always match its Certificate of Analysis.
- Benzyl alcohol
- The preservative component (0.9%) of bacteriostatic water. Bacteriostatic β it stops microbes multiplying rather than killing them outright.
- Biased agonism
- When different ligands at the same receptor preferentially trigger different downstream pathways (G-protein vs Ξ²-arrestin) β a frontier of incretin-receptor research.
- Blend
- Two or more peptides supplied in a single vial at fixed ratio β e.g. our CJC-1295 + Ipamorelin blend β used when research requires consistent molar ratios.
C
- Cell culture
- Growing cells outside an organism in controlled conditions β the workhorse setting of in-vitro peptide research.
- Chromatogram β
- The plot produced by a chromatography run: detector response against time, with each separated component appearing as a peak whose area reflects its amount.
- COA (Certificate of Analysis) β
- A batch-specific document listing the tests performed on one lot of material, the specification for each test and the result obtained.
- Cold chain
- Keeping temperature-sensitive product within a safe range from manufacture to delivery. Domestic express shipping keeps the Australian leg of the chain short.
- Copper peptide β
- A peptideβcopper(II) complex; in research usage usually GHK-Cu, the plasma tripeptide glycyl-L-histidyl-L-lysine bound to Cu2+, studied mainly in fibroblast and extracellular-matrix work.
- Counter-ion β
- An ion of opposite charge that balances a peptide's charged groups in the solid state; in synthetic peptides it is usually trifluoroacetate, acetate or chloride.
- Crimp seal
- The aluminium band locking a rubber stopper to a vial, applied at filling under inert conditions. An intact crimp is your evidence of an unopened vial.
- Cyclic peptide
- A peptide whose chain loops back on itself via an internal bond, adding stability and conformational rigidity β Melanotan II is the classic research example.
D
- Dalton (Da) β
- The unit of molecular mass: one dalton (Da) is one-twelfth the mass of a carbon-12 atom, about 1.66 Γ 10β»Β²β΄ g, so a molecule of X Da has a molar mass of X g/mol.
- Deamidation β
- Non-enzymatic loss of the side-chain amide from asparagine (or, more slowly, glutamine), converting it to aspartate or isoaspartate and adding a negative charge.
- Diluent
- The liquid used to dissolve lyophilised material β bacteriostatic water for multi-use research vials.
- DPP-4
- Dipeptidyl peptidase-4, the enzyme that rapidly cleaves native incretins. Resisting DPP-4 is a core design goal of GLP-1 analogues.
E
- Endotoxin β
- Lipopolysaccharide from the outer membrane of Gram-negative bacteria; a potent trigger of innate immune cells that survives sterilisation and can confound in-vitro assays.
F
- Fragment
- A defined section of a larger protein studied in isolation β AOD-9604 (hGH 176-191) and TB-500 (thymosin Ξ²4 fragment) are both fragments.
- Freezeβthaw cycle β
- One pass of a solution from liquid to frozen and back; each pass exposes dissolved peptide to freeze-concentration, ice and pH stresses, so labs keep the count low.
G
- Ghrelin mimetic
- A compound that activates the ghrelin receptor (GHS-R). Ipamorelin is the classic selective example in research.
- Ghrelin receptor β
- The class A G protein-coupled receptor (GHS-R1a) for the stomach hormone ghrelin; it signals with high activity even when unbound and is the target of ipamorelin and the GHRPs.
- GHRH β
- Growth hormone-releasing hormone: a 44-residue hypothalamic peptide that drives growth hormone synthesis and release through the GHRH receptor on pituitary somatotrophs.
- GIP
- Glucose-dependent insulinotropic polypeptide β the second incretin. Tirzepatide targets both GIP and GLP-1 receptors.
- GIP receptor β
- The class B G protein-coupled receptor for glucose-dependent insulinotropic polypeptide (GIP); it couples to GΞ±s and cAMP and is one target of dual and triple incretin agonists such as tirzepatide.
- GLP-1
- Glucagon-like peptide-1, an incretin hormone. The receptor target of semaglutide and one of three targets of retatrutide.
- GLP-1 receptor β
- The class B G protein-coupled receptor activated by glucagon-like peptide-1; it signals mainly through GΞ±s and cAMP and is the target of semaglutide and other incretin analogues.
- Glucagon receptor β
- The class B G protein-coupled receptor for glucagon, acting mainly in the liver; it signals through cAMP and calcium and is the third target of triple agonists such as retatrutide.
- Growth hormone secretagogue β
- Any compound that triggers growth hormone release; in research usage, mainly the synthetic ghrelin-receptor agonists such as GHRP-6, ipamorelin and MK-0677, as distinct from GHRH analogues.
H
- Half-life β
- The time taken for the concentration of a compound to fall to half its starting value; for peptides it can describe clearance from the body, breakdown in plasma or loss in an assay medium.
- HPLC β
- A separation technique that pumps a dissolved sample through a packed column and detects each component as it elutes; the standard method for measuring peptide purity.
- Hygroscopic
- Readily absorbing atmospheric moisture β NAD+ notably is. Reseal hygroscopic vials quickly and store dry.
I
- In-vitro β
- Latin for "in glass": experiments on molecules, cells or tissues outside a living organism, such as receptor-binding assays, enzyme assays and cell culture.
- Incretin
- Gut hormones (GLP-1, GIP) released after eating that amplify insulin signalling. The compound class behind semaglutide, tirzepatide and retatrutide.
- Insulin syringe
- The fine-gauge (29-31G) small-volume syringe standard in peptide handling for its precise graduations.
- Isoelectric point β
- The pH at which a peptide's positive and negative charges cancel, giving zero net charge; solubility is usually lowest near this pH.
L
- Ligand
- Any molecule that binds a receptor β every research peptide in a binding study is a ligand.
- Lyophilisation β
- Freeze-drying: removing water from a frozen solution by sublimation under vacuum, leaving a dry, porous solid that keeps far longer than the same peptide in solution.
M
- Mass spectrometry (MS) β
- An analytical technique that ionises molecules and measures their mass-to-charge ratio (m/z); for peptides it confirms identity by matching measured mass to the mass calculated from the sequence.
- Melanocortin
- The receptor family (MC1R-MC5R) targeted by Melanotan II and PT-141, spanning pigmentation and CNS signalling research.
- Melanocortin receptor β
- Any of five class A G protein-coupled receptors (MC1RβMC5R) activated by ACTH and the melanocyte-stimulating hormones; studied with ligands such as melanotan II and PT-141.
- Molar ratio
- The proportion of molecules (not milligrams) between compounds in combination work β what fixed-ratio blend vials hold constant.
- Molarity β
- Concentration expressed as moles of solute per litre of solution (mol/L, written M); peptide work usually uses millimolar (mM), micromolar (Β΅M) or nanomolar (nM).
- Molecular weight β
- The mass of one mole of a substance in grams (g/mol), numerically equal to the average mass of one molecule in daltons; the figure that converts milligrams into moles.
N
- N-terminus / C-terminus
- The two ends of a peptide chain β amino end and carboxyl end. Sequences are written N to C.
- Net peptide content β
- The percentage of a lyophilised peptide powder's weight that is the peptide itself, once counter-ions, bound water and other non-peptide material are excluded.
P
- Peptide
- A chain of 2-50 amino acids. Longer chains are proteins. Research peptides are synthesised copies of natural signalling molecules or engineered analogues.
- Peptide aggregation β
- Self-association of peptide molecules into oligomers, amorphous precipitates or ordered fibrils, removing them from the dissolved, monomeric pool an experiment assumes.
- Peptide bond β
- The amide bond joining the carboxyl group of one amino acid to the amine group of the next, formed with the loss of one molecule of water.
- Peptide mapping
- Analytical fingerprinting of a peptide by controlled fragmentation β an orthogonal identity method to MS.
- Peptide oxidation β
- Chemical modification of susceptible side chains, chiefly Met, Cys and Trp, by oxygen species; it adds mass (typically +16 Da) and can change structure and activity.
- Peptide purity β
- The proportion of peptide-related material in a sample that is the intended sequence, normally reported as the main peak's share of total HPLC peak area.
- Peptide sequence β
- The order of amino acids in a peptide chain, written by convention from the N-terminus (free amine) on the left to the C-terminus (free carboxyl) on the right.
- Proteolysis
- Enzymatic breakdown of peptides and proteins β the fate all peptide engineering works to delay.
- Purity (β₯99%)
- The HPLC main-peak area as a percentage of total peak area. Our release specification for peptides is β₯99%.
R
- Receptor
- A protein that receives chemical signals. Most peptide research is receptor research: binding, activation, downstream signalling.
- Receptor internalisation
- A cell pulling an activated receptor inside β desensitisation machinery, measurable in vitro, central to agonist-comparison studies.
- Reconstitution β
- Dissolving a lyophilised peptide in a measured volume of solvent to make a stock solution of known concentration.
- Reference standard
- A verified authentic sample used to calibrate analytical runs β what your batch is compared against in HPLC.
- Research use only (RUO)
- The legal category of every product we sell: laboratory reagents for in-vitro research, not for human or veterinary use.
- Retention time β
- The time between injecting a sample and the apex of a component's peak on an HPLC trace; characteristic of a molecule only under one fixed method.
S
- Scratch-wound assay
- An in-vitro migration model: a gap is scratched in a cell monolayer and closure is timed β a staple of repair-peptide research.
- Secretagogue
- A substance that causes another substance to be secreted. GH secretagogues (ipamorelin, GHRP class) are a major research family.
- Selectivity
- How exclusively a compound hits its intended target versus related receptors β ipamorelin's claim to fame.
- Sirtuins
- NAD+-dependent enzymes tied in the literature to DNA repair and metabolic regulation β a pillar of NAD+ research interest.
- Solubility β
- The highest concentration at which a peptide stays in true solution under stated conditions of solvent, pH, ionic strength and temperature.
- SPPS β
- The standard way to make synthetic peptides: amino acids are added one at a time to a chain anchored on insoluble resin beads, with excess reagents washed away after each step.
- Sterile filtration β
- Removing microorganisms from a heat-sensitive solution by passing it through a membrane rated at 0.2 or 0.22 Β΅m, without heating the solute.
- Sterile water β
- Purified water that has been sterilised and contains no preservative, buffer or salt; the default diluent when nothing besides water should enter an experiment.
- Stock solution
- The concentrated parent solution from which working dilutions are made β reconstitute once, dilute as needed.
T
- Telomere
- The protective repeat sequence capping chromosomes, shortening with cell division β the subject of epithalon's research literature.
- Trifluoroacetic acid β
- A strong, volatile acid (CF3COOH) used to cleave peptides from synthesis resin and in HPLC purification; its anion, trifluoroacetate, is the usual counter-ion in synthetic peptides.
- Truncated sequence
- A synthesis error product missing amino acids β the main impurity class HPLC screening catches.
U
- USP
- United States Pharmacopeia β the quality standard our bacteriostatic water meets.
V
- Vehicle
- The neutral carrier a compound is delivered in during experiments β the control arm ('vehicle only') every good study includes.
- Vial (lyophilised)
- The sealed glass container of freeze-dried peptide under inert conditions, with crimp seal and flip-off cap.
W
- Working solution
- The diluted, ready-to-use solution prepared from stock for a specific experiment.
Ξ
- Ξ±-MSH
- Alpha-melanocyte-stimulating hormone β the natural ligand of melanocortin receptors and structural parent of Melanotan II and PT-141.
Ξ
- Ξ²-arrestin
- A signalling protein recruited to activated GPCRs, driving receptor internalisation and a second signalling arm β central to biased-agonism research.
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