Peptide research glossary: plain definitions of common terms

Peptide papers and certificates use a lot of specialised language. This glossary gives short, plain definitions of the terms that come up most often, with links to fuller articles. Definitions can be narrower in a particular method or standard, so check the source document when a term really matters.

The molecule

Amino acid

A small organic molecule and the building block of peptides and proteins. Twenty standard amino acids are used in nature.

Peptide

A chain of amino acids joined by peptide bonds. Peptides are usually shorter than proteins, often under about fifty residues, though the line is not exact. See what are research peptides.

Residue

One amino acid as part of a chain. A "fifteen-residue peptide" has fifteen amino acids.

Sequence

The order of amino acids in a chain, written from the N-terminus to the C-terminus.

Analogue

A peptide based on a natural sequence with one or more changes, made to alter stability or behaviour in a model.

Synthetic peptide

A peptide made in a laboratory, usually by solid-phase synthesis, rather than isolated from a natural source.

Lyophilized

Freeze-dried. Research peptides are supplied as a lyophilized powder because they are far more stable dry. See storing lyophilized peptides.

Counter-ion

A charged molecule, such as acetate or trifluoroacetate, paired with the peptide in its salt form.

Testing

Certificate of analysis (COA)

A report of the tests carried out on one batch, with methods and results. See how to read a certificate.

Batch or lot

A quantity of material made in one production run. Test results apply to one batch. See batch numbers.

HPLC

High-performance liquid chromatography, a method that separates the components of a sample. Used to measure purity. See HPLC and peptide purity.

Mass spectrometry (MS)

A method that measures the mass of molecules. Used to confirm identity. See mass spectrometry for peptide identity.

LC-MS

Liquid chromatography combined with mass spectrometry, so components are separated and then measured.

Identity

Evidence that a material is the intended molecule.

Purity

The share of the detected material that is the target peptide, as measured by a stated method, usually HPLC. See what a purity percentage means.

Net peptide content

The share of the total powder weight that is peptide, as opposed to water and counter-ions.

Impurity

Any component other than the intended molecule, such as a shortened chain or an oxidised form.

Endotoxin

A component of certain bacteria's outer membrane, measured with its own test. See what each contamination test can detect.

Detection limit

The smallest amount a method can reliably detect. "Not detected" means below this limit.

Assay

A defined procedure that measures a property or an activity.

Research

In vitro

Research outside a living organism, such as in a tube or a dish of cultured cells.

In vivo

Research inside a living organism, usually an animal model in early research. See in vitro, in vivo and clinical research.

Clinical trial

A study with human participants, designed to answer a defined question.

Receptor

A protein that recognises and binds a particular molecule, often passing a signal into the cell. See how peptides work.

Agonist and antagonist

An agonist binds a receptor and activates it; an antagonist binds it and blocks it.

Endpoint

The outcome a study measures to answer its question.

Control group

A group treated the same way as the test group except for the variable being studied.

Reproducibility

Getting consistent results when an experiment is repeated, ideally by an independent group.

Peer review

Review of a paper by other researchers before publication. A quality check, not proof that the findings are correct. See how to evaluate peptide studies.

Browse the catalogue

Peptune publishes certificates of analysis on each product page as they arrive, and in the certificate library. Browse the full catalogue.

For laboratory research use only. Nothing in this article is medical advice or a suggestion to use any compound on people or animals.