Peptide Glossary: 40 Terms Every Researcher Should Know

A plain-language glossary of the terms you will meet when reading about research peptides, product listings and certificates of analysis.

Research Peptide Guide

Key takeaways

Terms are grouped alphabetically.
Each definition is written for a general technical reader.
Follow the links to guides that explore a topic in more depth.

Glossary

Acetylation: Adding an acetyl group, often to the N-terminus of a peptide, to change stability or charge.
Agonist: A compound that binds a receptor and activates it.
Aliquot: A small portion of a prepared solution stored separately to avoid repeated freeze–thaw cycles.
Amidation: Replacing a peptide’s C-terminal carboxyl group with an amide. Product names often say “amidate”.
Amino acid: The building block of peptides and proteins, containing an amino group, a carboxyl group and a side chain.
Analog: A modified version of a natural peptide made by changing its amino acids or adding chemical groups.
Antagonist: A compound that binds a receptor and blocks its activation.
Bacteriostatic water: Sterile water containing 0.9 percent benzyl alcohol as a preservative. See our guide.
Batch: See Lot.
CAS number: A unique numeric identifier assigned to a chemical substance by the Chemical Abstracts Service.
Certificate of analysis (COA): A document reporting test results for a specific batch. See how to read one.
Counter-ion: A charged species, such as trifluoroacetate or acetate, that accompanies a peptide salt.
Cyclic peptide: A peptide whose ends or side chains are joined to form a ring.
DAC (drug affinity complex): A chemical group that lets a peptide bind albumin and extends its activity, as used in CJC-1295 with DAC.
Diluent: The liquid used to dissolve or dilute a lyophilized powder.
DPP-4: Dipeptidyl peptidase-4, an enzyme that rapidly degrades GLP-1 and GIP.
Endotoxin: Fragments of bacterial cell walls that can affect cell-culture experiments; tested by the LAL assay.
GHRH: Growth hormone-releasing hormone, the hypothalamic peptide that stimulates GH release.
Ghrelin: A stomach-derived hormone that stimulates GH release through GHS-R1a.
GIP: Glucose-dependent insulinotropic polypeptide, an incretin hormone.
GLP-1: Glucagon-like peptide-1, an incretin hormone. See GLP and GIP peptides explained.
Half-life: The time taken for the concentration of a compound to fall by half.
HPLC: High-performance liquid chromatography, the standard method for peptide purity. See our guide.
Hygroscopic: Tending to absorb moisture from the air.
Incretin: A gut hormone that enhances insulin secretion after a meal.
Lot: One production batch of a material, identified by a lot number.
Lyophilization: Freeze-drying: removing water from a frozen solution under vacuum to leave a stable powder.
Mass spectrometry: A technique that measures the mass-to-charge ratio of ions to determine molecular mass.
Melanocortin: A family of peptides derived from POMC, including ACTH and the MSH peptides.
Net peptide content: The fraction of a vial’s powder that is peptide rather than water or counter-ions.
Oxidation: A chemical degradation pathway that affects residues such as methionine, cysteine and tryptophan.
PEGylation: Attaching polyethylene glycol to a molecule to extend its half-life.
Peptide: A short chain of amino acids linked by peptide bonds.
Peptide bond: The amide bond that joins the carboxyl group of one amino acid to the amino group of the next.
Reconstitution: Dissolving a lyophilized powder in a diluent.
Research use only (RUO): A label indicating material is for laboratory research and not for human or animal use.
Secretagogue: A substance that causes another substance to be secreted.
Solid-phase peptide synthesis (SPPS): Building a peptide one amino acid at a time on an insoluble resin.
TFA salt: A peptide supplied with trifluoroacetate counter-ions left over from HPLC purification.