Peptide Research Glossary
The terms that appear on certificates, product pages and in the literature, defined plainly, with links to the longer explanations.
Terms that appear on certificates of analysis, product pages and in the research literature, defined plainly. Where a term has a longer article behind it, the link follows the definition.
A–C
Acetylation (N-terminal) — attaching an acetyl group to the free amine at a peptide’s N-terminus, blocking aminopeptidase attack. Written as Ac- at the start of a sequence.
Aib — α-aminoisobutyric acid, a non-proteinogenic amino acid with two methyl groups on the alpha carbon. Adds steric bulk that blocks DPP-4 cleavage and promotes helical structure. Used in GLP-III and ipamorelin.
Aggregation — irreversible association of peptide molecules with each other, driven by air–liquid interfaces, freeze–thaw cycling, high concentration and pH near the isoelectric point. Not reversed by dilution. Full article.
Amidation (C-terminal) — converting the terminal carboxylic acid to an amide, blocking carboxypeptidase attack. Written as -NH2.
Bacteriostatic water — sterile water containing 0.9 per cent benzyl alcohol as a preservative, allowing repeated access to a vial over weeks. Cytotoxic; unsuitable for cell culture. Full article.
Batch (lot) — material produced in a single manufacturing run under one set of conditions. Analytical results apply to the batch tested and to no other. Full article.
COA — certificate of analysis. A document reporting analytical results for a specific batch. Meaningful only when the batch number matches the vial. Full article.
Counter-ion — an oppositely charged ion associated with a peptide’s charged groups, usually trifluoroacetate. Accounts for 5–20 per cent of vial mass. Full article.
D–H
Deamidation — spontaneous conversion of asparagine or glutamine side chains to aspartate or glutamate, adding 1 Da. Accelerated above pH 7.
Deletion sequence — a chain missing one residue, produced when a coupling step is incomplete. The dominant impurity class in synthetic peptides, and structurally close enough to the product to be hard to separate.
DPP-4 — dipeptidyl peptidase-4, an enzyme that removes the first two N-terminal residues from susceptible peptides. The main clearance route for incretin and GHRH peptides, and the target of most half-life engineering.
Endotoxin — lipopolysaccharide from Gram-negative bacterial membranes. Heat-stable, invisible to HPLC, active at picogram levels in cell work. Measured in EU/mg. Full article.
ESI — electrospray ionisation, the mass spectrometry method that produces multiply charged ions and couples directly to HPLC. Full article.
Fmoc — fluorenylmethyloxycarbonyl, the base-labile protecting group used in the dominant solid-phase synthesis strategy.
GHS-R1a — the growth hormone secretagogue receptor, target of ghrelin and of the GHRP class. Distinct from the GHRH receptor. Full article.
Half-life (t½) — the time for plasma concentration to fall by half. Not the same as duration of effect. Full article.
HPLC — high-performance liquid chromatography. Separates by hydrophobicity and gives purity as area percent. Full article.
I–P
Isoelectric point (pI) — the pH at which a peptide carries no net charge and solubility is at its minimum. Most dissolution failures are a peptide sitting at its pI. Full article.
Lactam bridge — a covalent amide link between two side chains, cyclising a peptide. More stable than a disulfide: does not scramble or reduce. Mass signature −18 Da.
Lyophilisation — freeze-drying. Removes water by sublimation under vacuum, leaving a glassy solid. The reason sealed peptide is stable at ambient temperature. Full article.
MALDI — matrix-assisted laser desorption/ionisation. Produces mostly singly charged ions; tolerant of salts.
Norleucine (Nle) — a methionine analogue with no sulfur, used to eliminate oxidation. Seen in Melanotan II.
Peptide content — the fraction of vial mass that is actually peptide, typically 75–90 per cent. A different question from purity. Full article.
Purity (HPLC, area %) — the main peak’s area divided by total integrated peak area. Relative, not absolute: says nothing about counter-ions or water.
R–Z
Reconstitution — dissolving lyophilised peptide in a solvent. Full article.
Research use only — a regulatory position, not a disclaimer. EU law classifies by intended purpose, so a research chemical is regulated under REACH and CLP rather than as a medicinal product. Full article.
Scrambling — a disulfide exchanging partners to give an isomer with identical mass and the wrong structure. Not detectable by mass spectrometry. Full article.
SPPS — solid-phase peptide synthesis. Chains are built on an insoluble resin, C-terminus first. Full article.
TFA — trifluoroacetic acid. Used in cleavage and as an HPLC mobile-phase additive; the default counter-ion on conventionally purified peptide. Cytotoxic at sufficient concentration.
Theoretical vs observed mass — the mass calculated from the sequence versus the mass measured. Agreement confirms identity; common discrepancies are +16 (oxidation), +1 (free acid or deamidation), −18 (water loss) and −57 to −186 (a deletion).
All products and information referenced are for in-vitro research and laboratory use only. Nothing here is medical advice, and no therapeutic claim is made or implied.