Research Peptide Glossary

Acylation: Attaching a fatty-acid chain to a peptide, usually on a lysine side chain, so it binds serum albumin and circulates for days instead of minutes. Semaglutide, tirzepatide and retatrutide are all acylated. See the GLP-1 family comparison.
Aib: α-Aminoisobutyric acid, a non-natural amino acid placed at position 2 of many GLP-1 analogues and at the N-terminus of ipamorelin to block enzymatic cleavage.
Agonist: A molecule that binds a receptor and activates it. A dual or triple agonist activates two or three receptor types with one molecule.
Albumin: The most abundant protein in blood plasma, with a half-life of about three weeks. Peptides that bind it, whether by acylation or a covalent linker, inherit part of that persistence.
Bacteriostatic water: Sterile water containing 0.9% benzyl alcohol, a preservative that stops bacteria introduced by repeated punctures from multiplying. See bacteriostatic vs sterile water.
Batch, lot: One production run of a compound. A certificate of analysis belongs to a batch, not a product; the batch number on the certificate must match the vial label.
Blend: Two or more compounds in one vial at a fixed ratio. A blend is assayed component by component and has no single purity figure.
CAS number: The Chemical Abstracts Service registry number, a unique identifier for a chemical substance. Listed for every single compound on the reference table.
Certificate of analysis (COA): The report a laboratory issues for one batch, stating what was measured and the result. See how to read a certificate of analysis.
Counter-ion: The negatively charged ion that balances the positive charges on a peptide's basic residues in the dry powder, usually trifluoroacetate or acetate. It contributes to the gross mass without being peptide.
DAC: Drug Affinity Complex: a maleimide-bearing group that bonds a peptide to serum albumin after administration. See CJC-1295 with and without DAC.
Deamidation: A slow chemical change in which an asparagine or glutamine side chain loses its amide group, converting it to aspartate or glutamate. Faster in solution at neutral-to-alkaline pH; one reason solutions are refrigerated and used promptly.
Deletion sequence: A synthesis impurity missing one amino acid, produced when a coupling step fails on some chains. Hard to separate because it is nearly identical to the product. See how research peptides are made.
DPP-4: Dipeptidyl peptidase-4, the enzyme that inactivates native GLP-1 and GHRH within minutes by clipping two residues from the N-terminus. Most analogues are engineered to resist it.
Fmoc: The protecting group used on the amine of each incoming amino acid in modern solid-phase peptide synthesis. Removed with a mild base at the start of every cycle.
GHRH: Growth-hormone-releasing hormone, the hypothalamic peptide that drives pituitary growth-hormone release. CJC-1295, tesamorelin and sermorelin are analogues of it. See the secretagogue comparison.
Ghrelin receptor (GHS-R1a): The second receptor through which growth hormone can be released. Ipamorelin and the GHRP series act here rather than on the GHRH receptor.
GLP-1, GIP: The two incretin hormones released by the gut after a meal. Semaglutide acts on the GLP-1 receptor; tirzepatide on both; retatrutide on both plus the glucagon receptor.
Half-life: The time for the concentration of a compound in plasma to fall by half. Native GHRH: minutes. Acylated GLP-1 analogues: about a week.
HPLC: High-performance liquid chromatography, the technique behind every purity figure. See reading an HPLC chromatogram.
Lyophilisation: Freeze-drying: removing water from a frozen solution by sublimation under vacuum, leaving a porous solid cake. See why peptides are freeze-dried.
Mass spectrometry: Measurement of a molecule's mass. On a certificate it confirms identity: the observed mass must match the theoretical mass of the intended sequence.
Melanocortin receptors: The five receptors (MC1R to MC5R) acted on by α-MSH and its analogues. See melanocortin peptides.
Net peptide content: The fraction of a powder's gross mass that is actually peptide, after counter-ion and bound water are excluded. Routinely well below 100% and often not reported.
Oxidation: Chemical damage to methionine, cysteine or tryptophan residues by oxygen or light. The product pages flag which sequences carry these residues.
Purity: On a certificate, the area of the main HPLC peak as a percentage of all peaks. A measure of how clean the peptide is relative to other peptides, not of how much of the powder is peptide.
Reconstitution: Dissolving the lyophilised cake in a diluent to a known concentration. See the reconstitution calculator.
Research use only (RUO): The condition under which every product on this site is sold: for laboratory research, not for human or veterinary use, and not approved for any use by any regulator.
Retention time: The time at which a compound elutes from an HPLC column under a given method. Reproducible within a laboratory, not transferable between them.
Sequence: The order of amino acids in a peptide, written with three-letter codes. Modifications such as Ac- (acetyl), -NH2 (amide) and D- (D-amino acid) are written where they occur.
TFA salt: The form in which most synthetic peptides are supplied: the peptide with trifluoroacetate counter-ions left from cleavage and HPLC purification.
Third-party test: An analysis by a laboratory independent of the manufacturer, run on a sample of the finished product. The certificates on our product pages are of this kind and carry the laboratory's verification key.
Verification key: A code printed on a third-party test report that lets anyone confirm the report against the laboratory's own records. Every certificate we show includes one.

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