Science

What a peptide is

A peptide is a sequence of amino acids joined by peptide bonds, shorter than a full protein. Sequence determines structure, and structure determines how a molecule behaves in an assay. Two vials labeled with the same name are not equivalent unless both have been characterized.

How they are made

Research peptides are typically produced by solid-phase peptide synthesis: the chain is assembled one residue at a time on a solid support, then cleaved, purified and dried. Purification is most commonly by reversed-phase high-performance liquid chromatography (HPLC). The result is supplied as a lyophilized — freeze-dried — powder, which is far more stable in transit and storage than a solution.

How they are characterized

These results are specific to a lot. A certificate for one lot says nothing about another.

• Identity — mass spectrometry confirms the molecule present is the molecule named.
• Purity — HPLC separates the target peptide from synthesis-related impurities and reports it as a percentage of total peak area.
• Net content — the actual mass of peptide in the vial, which is not the same as the fill weight.
• Contaminants — heavy metals, residual solvents, endotoxin and sterility, depending on the panel run.

Why lyophilized, and why sealed

Freeze-drying removes water, which is what most degradation pathways need. Vials are sealed and supplied with desiccant so the powder stays dry until the researcher chooses to reconstitute it. This is also why the material travels reliably at ambient temperature.

Reading a certificate of analysis

A certificate should name the lot, state what was tested, state the method used, and be traceable to the laboratory that produced it. A purity figure with no lot number and no issuing laboratory is a marketing claim, not a result.