What Are Peptides?

For in-vitro laboratory research use only. Not for human or veterinary use.

A peptide is a short chain of amino acids joined together by peptide bonds. This guide explains the chemistry in plain English: how the bonds form, how peptides differ from proteins, and how research peptides are made, tested and documented. For more introductory guides, visit our Knowledge hub.

What is a peptide?

The US National Human Genome Research Institute defines a peptide as a short chain of amino acids, typically 2 to 50, linked by peptide bonds (NHGRI glossary). Peptides are named by length: a dipeptide has two amino acids, a tripeptide three, a pentapeptide five. The molecule in the image above, Leu-enkephalin, is a naturally occurring pentapeptide with the sequence Tyr-Gly-Gly-Phe-Leu.

What makes one peptide different from another is its sequence: which amino acids are present and in what order. The same amino acids in a different order make a different compound.

Amino acids and the peptide bond

Amino acids are the building blocks. Each one has a central carbon atom carrying an amino group (–NH₂), a carboxyl group (–COOH), a hydrogen atom and a side chain, often written as “R”. Around twenty standard amino acids are used to build proteins in living cells.

A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of the next. A molecule of water is released, so chemists call this a condensation reaction. The new carbon–nitrogen link is an amide bond, known in this context as a peptide bond (Britannica). Repeating the reaction builds a backbone of repeating –N–C–C(=O)– units.

Every peptide chain has two distinct ends. The N-terminus carries the free amino group and the C-terminus carries the free carboxyl group. By convention, sequences are written from the N-terminus to the C-terminus, so “Tyr-Gly-Gly-Phe-Leu” starts with tyrosine at the amino end.

Peptide vs protein

Peptides and proteins are made the same way, from amino acids joined by peptide bonds. The difference is mainly size, and the dividing line is a convention rather than a strict rule. A common working definition is that chains of up to about 50 amino acids are peptides, while longer chains are polypeptides or proteins. Britannica notes that the distinction between a polypeptide and a protein is “imprecise and largely academic”.

In practice, longer chains usually fold into stable three-dimensional shapes, while short peptides are small enough to be made entirely by chemical synthesis.

Natural, synthetic and analogue peptides

Peptides can be grouped by where their sequence comes from:

• Naturally occurring peptides are sequences found in living organisms, such as glutathione (three amino acids) or Leu-enkephalin (five).
• Synthetic peptides are made in the laboratory. A synthetic peptide can copy a natural sequence exactly, or it can be a sequence designed or derived for research. For example, BPC-157 is a synthetic chain of 15 amino acids.
• Analogues are peptides whose structure has been deliberately modified compared with a parent sequence. Examples include swapping an amino acid, using mirror-image (D-) amino acids, capping either end (acetylation or amidation) or cyclisation. Each change creates a distinct compound with its own molecular mass.

Some research products combine two peptides in one listing, for example TB-500 with BPC-157. In that case the documentation should identify each component and its amount.

Regulation depends on how a product is presented and supplied, not on the word “peptide”. In the UK, the MHRA publishes guidance on how it decides whether a product is a medicine (GOV.UK: Borderline products). The research peptides in our shop are research chemicals supplied for laboratory use only. They are not medicines, food or supplements.

How peptides are made

Most research peptides are made by solid-phase peptide synthesis (SPPS), a method developed by Robert Bruce Merrifield, who received the 1984 Nobel Prize in Chemistry for it (NobelPrize.org). The first amino acid is anchored to tiny insoluble resin beads. The chain is then built one amino acid at a time. Each new amino acid carries a temporary protecting group (usually Fmoc or Boc) so it joins in only one place; the group is removed and the cycle repeats, with excess reagents washed away between steps.

The finished chain is cleaved from the resin and purified, usually by preparative HPLC, to remove incomplete sequences.

Finally, the purified peptide is usually lyophilised (freeze-dried). The frozen solution is placed under vacuum so the ice turns straight to vapour, leaving a dry powder or “cake” in the vial. A lyophilised peptide is generally much more stable than the same peptide in solution, which is why research peptides are usually supplied this way.

How peptide purity is tested

Two analytical techniques do most of the work. You can see published batch results for each listed product on our COA and verification page.

• High-performance liquid chromatography (HPLC) separates the components of a sample on a packed column, usually reversed-phase with UV detection. The peptide bond absorbs UV light at low wavelengths (around 210–220 nm), so every peptide-containing component shows up as a peak on the chromatogram. Purity is reported as the area of the main peak as a percentage of the total peak area.
• Mass spectrometry (MS) measures the mass of the molecules in the sample. Comparing the observed mass with the theoretical mass of the sequence confirms the peptide’s identity. HPLC answers “how pure is it?”; MS answers “is it the right molecule?”.

How peptides are made and tested →

Reading a certificate of analysis

A certificate of analysis (COA) is the laboratory’s report on a specific batch. Look for:

• Product name and amount: the peptide and the quantity per vial (for example 10 mg).
• Batch or report number: this ties the certificate to a particular production lot.
• Laboratory, test date and method: usually HPLC, sometimes with MS.
• Purity result: given as a percentage, often with the measurement uncertainty.
• Identity: an observed mass compared with the theoretical mass, where MS is reported.
• Other tests: depending on the test, a certificate may also report results such as heavy metals, endotoxin or sterility.

Published Corex Vitality™ batches are tested by third-party laboratories, and you can search and download each listed certificate on our COA and verification page. On each product page, the View Lab COA button opens the published certificates for that compound; where your size has no COA of its own, the COA shown is for another batch size.

Storage basics for research vials

General laboratory principles:

• Lyophilised (powder) vials: for longer storage, keep unopened vials tightly closed in a freezer at −20 °C or colder, dry and away from light. A laboratory fridge (2–8 °C) is fine for vials you plan to open soon, and room-temperature transit is normal for dry peptides. Let a cold vial reach room temperature before opening, ideally in a desiccator, so condensation does not form; work quickly and reseal tightly.
• Reconstituted (in solution): once a peptide is dissolved it is much less stable than the dry powder. Make up only what you need. Split any solution you keep into labelled, dated single-use portions (aliquots), freeze them at −20 °C or colder and thaw each aliquot only once; avoid repeated freeze–thaw cycles. Sequences containing Cys, Met or Trp oxidise easily, and Asn or Gln shorten shelf life in solution. (General guidance paraphrased from Bachem’s handling and storage guidelines.)
• Always follow the product documentation and your institution’s own safety and handling procedures.

Full storage guide →

Glossary

• Amino acid: a building-block molecule with an amino group, a carboxyl group and a side chain.
• Peptide bond: the amide (C–N) bond that links one amino acid to the next.
• N-terminus / C-terminus: the amino end and the carboxyl end of a chain.
• Analogue: a peptide structurally modified from a parent sequence.
• SPPS: solid-phase peptide synthesis, building a chain on resin beads one amino acid at a time.
• Lyophilisation: freeze-drying, which removes water by sublimation under vacuum.
• Reconstitution: dissolving a lyophilised powder for laboratory work.
• HPLC: high-performance liquid chromatography, used to measure purity.
• Mass spectrometry (MS): a technique that measures molecular mass, used to confirm identity.
• COA: certificate of analysis, the laboratory’s test report for a batch.

Explore more in our Peptide Knowledge & Education Hub.

Research use only

For in-vitro laboratory research use only. Not for human or veterinary use. These products are research chemicals. They are not medicines, food, or supplements. They have not been evaluated by the MHRA, FDA, or any other regulatory body. Not intended to diagnose, treat, cure, or prevent any disease. All descriptions are for reference and research documentation purposes only.

Sources

1. National Human Genome Research Institute. Peptide – Talking Glossary of Genomic and Genetic Terms.
2. Encyclopaedia Britannica. Peptide.
3. NobelPrize.org. Press release: The 1984 Nobel Prize in Chemistry (R. Bruce Merrifield, solid-phase synthesis).
4. MHRA / GOV.UK. Borderline products: how to tell if your product is a medicine.