What are peptides?

Chains of amino acids

An amino acid is a small molecule with a fixed core and a variable side chain. Link two together and the bond between them is called a peptide bond — a nitrogen from one joined to a carbon from the next, releasing a molecule of water. Keep linking and you get a chain.

The distinction between a peptide and a protein is one of size, and the boundary is a convention rather than a law of nature. Chains of roughly 50 residues or fewer are usually called peptides; longer ones are called proteins. A chain of two is a dipeptide, three a tripeptide, and so on.

Why twenty — and why our name

Life on Earth builds its proteins from a set of twenty standard amino acids. Every organism, from a bacterium to a blue whale, reads the same genetic code and assembles the same twenty parts in different orders. Everything a protein does — its shape, its charge, what it binds — comes from the sequence in which those twenty are strung together.

Twenty parts is a small alphabet for such variety. A chain of just ten residues can be arranged in 20¹⁰ ways — over ten trillion distinct sequences. That combinatorial reach is why such short chains are interesting to study at all.

That set of twenty is where the name Amino20 comes from: the complete alphabet that every peptide in this catalog is spelled with.

Shading = side-chain character. “Ess.” marks the nine amino acids humans cannot synthesise and must obtain from diet.

How sequences are written

Each amino acid has a three-letter and a one-letter abbreviation, so a sequence can be written compactly. Chains are always written from the N-terminus (the free amino end) to the C-terminus (the free acid end) — the same direction the ribosome builds them, and the same direction a chemist assembles a synthetic one.

How synthetic peptides are made

Most research peptides are built by solid-phase peptide synthesis, a method Bruce Merrifield introduced in 1963 and received the Nobel Prize in Chemistry for in 1984. The first amino acid is anchored to a solid resin bead. Each subsequent residue is added in a repeating cycle: unmask the end of the growing chain, couple the next amino acid, wash away the excess. Because the chain stays bolted to the bead, every cycle can be washed clean before the next begins.

When the sequence is complete the chain is cleaved from the resin and purified. Each cycle is efficient but not perfect, so a long synthesis accumulates truncated and modified by-products — which is precisely why purity is measured rather than assumed.

How purity is verified

Two instruments answer two different questions, and a credible certificate of analysis carries both.

Purity alone proves nothing about identity, and identity alone proves nothing about purity. A certificate reporting only one, or reporting “high purity” without a number, is not telling you much. A certificate should also name the laboratory that ran the tests and the lot it applies to, since every batch is made separately.

What laboratories use them for

Short peptides are useful research tools because they are small, chemically defined, and can be made to an exact sequence. A researcher studying how a receptor recognises its natural partner can synthesise just the fragment that does the recognising, change one residue, and observe what happens in cultured cells. Work of this kind is done in vitro — in dishes, on cell lines, in tissue preparations — and in animal models.

The compounds in this catalog are grouped by the area of biology they are studied in:

• Cells & structure

  The internal scaffolding cells use to hold their shape and move, and how cells migrate in culture.

• Gut & tissue

  Laboratory models of the gastrointestinal lining and connective tissue.

• Immune & inflammation

  Molecular pathways cells use to switch inflammatory responses on and off.

• Brain & nerves

  Neurotransmitter and growth-factor signalling, chiefly in rodent models.

• Metabolism & mitochondria

  How cells produce and regulate energy, including mitochondrial signalling.

• Hormones & growth factors

  Receptor pharmacology of hormone-releasing and growth-factor pathways, in cell and animal models.

• Cell ageing & DNA

  Telomere biology, cell division limits, and circadian regulation.

What “research use only” means

A research-use-only reagent is made and sold for laboratory experiments. It has not been through the studies a regulator requires before a substance may be given to a person or an animal, and it is not manufactured to the standards that would apply if it were. Nothing in this catalog is approved by the FDA for any use in humans or animals, and none of it may lawfully be administered to either.

That is a statement about the entire category, not a formality attached to ours. It is also why we sell only to verified laboratories: the label is only meaningful if the customer base matches it.