Peptide glossary: 30 terms for understanding
A glossary of peptide terms: amino acids, peptide bond, analogue, agonist, HPLC, MS, COA, RUO, half-life and more. Explanations in English.
Key findings
- The glossary distinguishes between molecule, formulation, analytical method and regulatory status.
- Terms such as purity and stability are insufficient without a method and context.
- RUO denotes research use only, not a medicine.
- Understanding the terms helps when reading studies and documentation.
In brief: this glossary is for reading literature and documentation. Terms run from basics to analytics, documentation and regulation. Every term should be read in context; a single word is rarely enough for a conclusion.
Basics
1. Peptide
A peptide is a chain of amino acids linked by peptide bonds. Length and sequence determine the molecule’s identity. Peptides are shorter than proteins, although the boundary is not strict.
2. Amino acid
An amino acid is the basic unit of a peptide, with an amino group, a carboxyl group and a side chain. Their order determines the peptide’s properties.
3. Peptide bond
A peptide bond forms between the carboxyl group of one amino acid and the amino group of another; a water molecule is released. The chain is the basis for secondary and tertiary structure.
4. Sequence
The sequence is the order of amino acids, usually written with one-letter codes. A small change can mean a different molecule with different properties.
5. N-terminus and C-terminus
The N-terminus is the peptide’s start, with a free amino group; the C-terminus is the end with a free carboxyl group. Writing usually runs from N- to C-terminus.
6. Oligopeptide, polypeptide, protein
An oligopeptide is a short amino acid chain, a polypeptide a longer one, and a protein is usually larger and more structured. The boundaries are not uniform and vary between sources.
7. Analogue
An analogue is a molecule similar to another but differing in one or more amino acids or groups. It may have different stability, binding or half-life.
8. Agonist
An agonist is a substance that activates a receptor and triggers a response. It need not be identical to the natural ligand; it may act more strongly, more weakly or differently.
9. Antagonist
An antagonist binds to a receptor without activating it. It often acts by preventing agonist binding. The effect depends on the receptor and context.
10. Receptor
A receptor is a molecule to which a signalling substance binds and triggers a cellular response. Receptors can be membrane-bound or located inside the cell.
11. Half-life
The half-life is the time in which the amount of a substance is halved. For peptides it depends on sequence, modifications, route of use and environment. The figure alone does not show whether a substance is effective.
12. Bioavailability
Bioavailability describes what proportion of a substance reaches its site of action in active form. For peptides, degradation, membrane passage and stability complicate it.
Analytics
13. Lyophilisate
A lyophilisate is a dried material produced by freezing and sublimation. It allows longer stability but is sensitive to moisture and light.
14. Reconstitution
Reconstitution is redissolving a lyophilisate in an appropriate solvent. Preparation affects concentration and stability; details are part of the laboratory protocol. The procedure is described in the guide to storage and reconstitution.
15. Cold chain
The cold chain is temperature control from production to use. It matters because high temperatures and repeated warming accelerate peptide degradation.
16. Stability
Stability describes how long a substance retains its identity and quantity under specified conditions. It depends on temperature, moisture, light, pH and formulation.
17. HPLC
HPLC (high-performance liquid chromatography) separates sample components on a column. It is used to assess purity and impurities.
18. UV detection
UV detection measures light absorption at a given wavelength. For peptides, 214 or 220 nm is often used, depending on molecule and method.
19. Mass spectrometry (MS)
MS determines the mass of ionised molecules and their fragmentation pattern, helping confirm identity and distinguish similar compounds.
20. Chromatogram
A chromatogram is a graph showing the separation of components over time. Peak height and area and baseline shape matter for interpretation.
21. Purity
Purity is the proportion of the main component in the whole, often given as the percentage of main peak area. Without method, wavelength and chromatogram, the figure is incomplete.
22. LOD and LOQ
LOD (limit of detection) is the lowest concentration a method can still detect. LOQ (limit of quantification) is the lowest concentration that can be reliably measured.
23. Method validation
Validation demonstrates that a method is suitable for its intended use. It includes parameters such as accuracy, repeatability, specificity and linearity.
Documentation
24. COA
A certificate of analysis documents a specific batch. It contains analysis results, the method and the data linking the document to the sample.
25. Batch
A batch (lot) is a group of product from the same production run. The batch number links the vial to the analytical report.
26. Specification
A specification defines a product’s required properties: identity, purity, form, quantity and storage conditions. It is the criterion for accepting or rejecting a batch.
27. Traceability
Traceability is the ability to trace a product back to its source, batch, date and storage conditions. Without it, documentation cannot be attributed to a specific sample.
Regulation and use
28. RUO
RUO means Research Use Only: the material is exclusively for research use. It is not a medicine and is not intended for human use.
29. Medicine
A medicine is a substance or combination of substances intended to treat, prevent or diagnose a disease. The status of a medicine depends on regulation and intended use, not on the molecule alone.
30. WADA
WADA is the World Anti-Doping Agency. Its prohibited list is a sporting rule and differs from the status of a medicine or research chemical.
How to use the glossary
- For basics, start with What are peptides?.
- For analytics, read HPLC and mass spectrometry.
- For documentation, read How to read a certificate of analysis.
- For reading literature, use How to read a peptide study.
- For the legal and sporting framework, see Peptides in Croatia and Peptides and WADA.
Conclusion
The glossary is not a list of claims about effects but a tool for more precise reading: what the molecule is, how it was analysed, what the document links and in what framework it was used.
If a term is used without context, a wrong conclusion can quickly be drawn. With a definition and a source, the risk is smaller.
Frequently asked questions about this topic
What is a peptide?
What does RUO mean?
What is a COA?
What is a half-life?
How to cite
RuskiPeptidi Editorial Team. (2026). Peptide glossary: 30 terms for understanding. RuskiPeptidi.com. https://ruskipeptidi.com/blog/peptide-glossary/
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RuskiPeptidi Editorial Team
Content is prepared by the RuskiPeptidi.com editorial team based on primary scientific sources, regulatory documents and manufacturer data. Every article is reviewed before publication, and sources are listed at the end of the text.
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