The short answer
A peptide is a short chain of amino acids joined end to end. Amino acids are the small molecules that proteins are built from, and a peptide is the same kind of chain as a protein, only shorter. The shortest possible peptide has two amino acids. The longest run to a few dozen.
Amino acids and the peptide bond
Every amino acid has an amino group at one end and a carboxyl group at the other. When two amino acids join, the carboxyl group of one reacts with the amino group of the next, a molecule of water is released, and the link left behind is a peptide bond. Repeat that and the chain grows, one amino acid at a time.
Twenty amino acids are used to build proteins in nature. The order they are joined in is the sequence, and the sequence is what makes one peptide different from another. A peptide is usually written as its sequence: GHK is glycine, histidine, lysine.
Peptide or protein?
The difference is length, and the line between them is a convention, not a law of nature. Chains of up to about fifty amino acids are generally called peptides. Longer chains that fold into a stable three-dimensional shape are called proteins. Insulin, at 51 amino acids in two linked chains, sits right on the boundary and is called both.
Peptides in nature
The body makes thousands of peptides, and many of them are signals. Oxytocin is a peptide of nine amino acids. Glucagon has 29. They are released in one place, travel, and bind to a receptor somewhere else. That is why peptides interest researchers: a short, defined sequence that fits one receptor is a precise tool for studying what that receptor does.
How research peptides are made
Research peptides are built by solid-phase peptide synthesis, a method introduced by Bruce Merrifield in 1963 that later won him the Nobel Prize in Chemistry. The first amino acid is anchored to a resin bead and the rest are added one at a time, in order, until the sequence is complete. The finished chain is cut from the resin, purified and freeze-dried.
No synthesis is perfect. Some chains come out a residue short, or with one missing from the middle, and purification has to remove them. That is what a purity figure measures.
HPLC reports how much of the material is the intended peptide, and mass spectrometry confirms it is the right molecule. Both appear on a certificate of analysis: see reading a batch certificate.
The peptides in our range, by size
Each has its own explainer: GHK-Cu, ipamorelin, PT-141, BPC-157 and TB-500. KPV is covered in glow vs klow.
Four things that are all called peptides
- Collagen peptides are fragments of collagen protein, broken down and sold as a food supplement powder.
- Cosmetic peptides are ingredients in serums and creams, used at low concentrations in products for skin.
- Peptide medicines, such as insulin, are licensed and supplied on prescription.
- Research peptides are defined compounds supplied to laboratories with a certificate stating identity and purity.
They share the chemistry and little else. A research peptide is not a supplement, a cosmetic or a medicine, and is not a substitute for any of them.
Ours are sold for in-vitro laboratory research only. Are peptides legal in the UK? explains where the line sits, and the full range is in the shop.