A peptide is a short chain of amino acids — the same building blocks proteins are made from, just fewer of them. The convention is loose, but most researchers use "peptide" for chains under roughly 50 residues and "protein" for anything longer. Insulin, at 51 residues across two chains, sits almost exactly on that line, which is fitting: it was the first peptide ever used as a medicine.
What makes peptides interesting to researchers is specificity. Because they mirror the body's own signalling molecules, they tend to bind a narrow set of receptors rather than blanketing a system the way a small molecule often does. That specificity is exactly why purity matters so much: a 96% pure sample is not "almost 99%" — it is a sample with 4% of something unidentified in it.
How they are made
Nearly all research peptides today are produced by solid-phase peptide synthesis (SPPS), the method Bruce Merrifield invented in 1963 and won a Nobel Prize for in 1984. The peptide is assembled one amino acid at a time on a resin bead, then cleaved, purified by reverse-phase HPLC, and lyophilised into the white powder you receive in a vial.
Longer or more complex sequences may instead be produced recombinantly — expressed in E. coli or yeast and purified from the culture. Recombinant production is how commercial insulin has been made since 1982.
Reading a Certificate of Analysis
- Identity — mass spectrometry confirming the molecular weight matches the intended sequence.
- Purity — HPLC chromatogram with a percentage figure and a visible trace, not just a number on a letterhead.
- Appearance and solubility — what the lyophilised powder should look like and what it reconstitutes into.
- Batch or lot number — the single most important field. Without it, the COA cannot be tied to the vial in your hand.
- Date of analysis — a COA from two years ago tells you about a batch you did not buy.
A supplier that will not send a batch-matched COA is not a supplier with a paperwork problem. It is a supplier with a sourcing problem.
Handling and storage
Lyophilised peptides are generally stable at -20°C for extended periods and tolerate short ambient shipping windows. Once reconstituted, most are stored refrigerated and used within weeks, not months. Repeated freeze-thaw cycles are the most common avoidable cause of degradation in a research setting.
Research use only
Every compound listed on Likwid Labs is supplied strictly for laboratory and research purposes. Nothing on this site is approved by the FDA, and nothing here is intended to diagnose, treat, cure, or prevent any disease or to be administered to humans or animals.