A peptide is a short chain of amino acids joined end to end by peptide bonds. A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of the next and releases a molecule of water. The chain has a direction: it begins at the N-terminus, which has a free amino group, and ends at the C-terminus, which has a free carboxyl group.
How long is a peptide?
There is no strict cut-off. Chains of about 2 to 50 amino acids are usually called peptides. Very short chains have their own names: a dipeptide has two residues, a tripeptide three, and an oligopeptide up to about twenty. Our catalogue runs from the three-residue KPV to thymosin beta-4 at 43 residues.
Sequence is identity
A peptide is defined by the order of its amino acids, its sequence. Swap two residues and you have a different molecule. Sequences are written with three-letter codes (Gly-Glu-Pro) or one-letter codes (GEP). Many research peptides also carry modifications: D-amino acids, non-standard residues such as α-aminoisobutyric acid (Aib), an acetylated N-terminus, an amidated C-terminus, or a fatty-acid side chain.
How research peptides are made
Most research peptides are made by solid-phase peptide synthesis (SPPS). The chain is built one residue at a time on a resin bead, then cut off the resin and purified, usually by preparative HPLC. The purified peptide is freeze-dried to a stable powder.
How identity and purity are checked
Mass spectrometry confirms that the molecule has the expected mass. HPLC separates the target peptide from related impurities and measures their relative amounts. Both results appear on a certificate of analysis.
Quick quiz
For laboratory research use only. This article describes chemistry and handling. It does not describe human use.