Research peptides are synthetic amino-acid chains supplied as lyophilised powder for laboratory use: receptor ligands, assay calibrators, immunogens, blocking peptides and protease substrates. They are the largest product type in the research catalog and the reference point for every other type — labeled peptides are these molecules with a tag, antibodies are raised against them, and assay kits are calibrated with them. Choosing one correctly comes down to five specifications: sequence and modifications, purity, peptide content, salt form, and species.
How a research peptide is made, and why it matters
Almost everything in this catalog is produced by solid-phase peptide synthesis: the chain is assembled one residue at a time on a resin, with side chains held under protecting groups, then cleaved, deprotected and purified by preparative HPLC. Three consequences follow directly. Synthesis efficiency falls with length, so peptides beyond roughly 50 residues become expensive and harder to purify — longer sequences are often recombinant instead. Cleavage uses trifluoroacetic acid, so the product arrives as a TFA salt unless exchanged. And the failure products are deletion sequences differing by one residue, which is why purity is quoted by HPLC and identity confirmed separately by mass spectrometry.
The five specifications to check before ordering
| Specification | What it tells you | What to watch for |
|---|---|---|
| Sequence and modifications | The exact molecule, including N-terminal acetylation, C-terminal amidation, cyclisation and non-natural residues | An amidated and a free-acid C-terminus are different peptides with different activity |
| Purity (HPLC) | Percentage of peptide-related material that is the target sequence | ≥95% is standard for assays; ≥98% for quantitative standards. It says nothing about salt or water content |
| Peptide content | Fraction of the vial's gross mass that is actually peptide | Typically 70–90%. Counter-ion and residual water make up the rest — this determines real concentration |
| Salt form | TFA or acetate counter-ion | TFA is cytotoxic and antimicrobial at assay concentrations; acetate for cell and MIC work |
| Species and fill | Which organism's sequence, and how much peptide per vial | Match the model organism; microgram fills for assays, milligram for animal protocols |
Purity versus content: the distinction that changes your numbers
These are separate figures and confusing them is the most common quantitation error in peptide work. Purity — from the HPLC chromatogram — is the proportion of peptide-related material corresponding to the target sequence. Peptide content — from amino-acid analysis or nitrogen determination — is the proportion of the vial's total mass that is peptide at all. A vial labelled 1 mg at 98% purity and 80% content holds roughly 0.8 mg of peptide, not 0.98 mg. Reconstituting on gross mass therefore overstates concentration by about 20%, which propagates through every derived value. For qualitative work this rarely matters; for a standard curve or a reported potency it is decisive. HPLC purity explained and the COA guide cover both figures on a real certificate.
Modifications, and why the catalog lists them as distinct products
A modification is not a variant of the same item — it is a different molecule with a different molecular weight and often different pharmacology. C-terminal amidation reproduces the natural processed form of most neuropeptides and is required for full receptor activity in families such as NPY, CGRP and substance P. N-terminal acetylation blocks aminopeptidase attack and removes the positive charge at that end. Disulfide bridges define the fold of defensins, somatostatin and endothelin, and a linear reduced version behaves differently. Pyroglutamate formation, phosphorylation, biotinylation and D-amino-acid substitution all likewise create separate catalog entries. Reading a peptide sequence decodes the notation these are written in.
Full-length, fragment or analog
Most family pages offer all three, and they answer different questions. The full-length native peptide is the right choice for standard curves, quantitation and physiological agonist work. A fragment is usually a receptor-subtype tool: CGRP(8–37) is an antagonist, PYY(3–36) is Y2-selective, AgRP(83–132) is the active core. Fragments are not cheaper substitutes for the parent. An analog — D-amino-acid substituted, stapled, PEGylated or otherwise stabilised — trades native identity for stability or selectivity, and is appropriate when a peptide must survive a plasma incubation or a longer in-vivo protocol. Browse the type page for what exists in a given family, and see the peptide libraries type when you need a systematic set rather than individual sequences.
Reconstitution, solubility and storage
Solubility is set by sequence, not by wishing. Highly charged hydrophilic peptides dissolve directly in water or buffer; basic peptides go into dilute acetic acid, acidic ones into dilute ammonium hydroxide; hydrophobic sequences generally need DMSO or acetonitrile first, then dilution into aqueous buffer. Check the isoelectric point — solubility is at its worst near it. Practical steps are in peptide solubility and the reconstitution guide; the molarity arithmetic is in molecular weight and moles.
Storage is simpler. Sealed lyophilised vials keep for years at −20 °C or below, protected from light and moisture — always let a vial reach room temperature before opening, or condensation will draw water into the powder. Reconstituted peptide is far less stable: aliquot into single-use volumes immediately and freeze, avoiding repeated freeze–thaw. Methionine, cysteine and tryptophan residues oxidise in solution, so minimise headspace and light exposure. See the storage guide, the aliquoting guide and common reconstitution mistakes.
Where research peptides fit against the other product types
Use a peptide standard when you need to apply a known quantity, calibrate an assay, or raise or absorb an antibody. Add a labeled peptide when detection requires a tag — binding assays, imaging, protease substrates. Order an antibody when you need to detect the endogenous molecule in tissue or on a blot. Order an assay kit when the question is how much endogenous peptide is present in a sample. Start from the catalog hub, or from a topic such as neuropeptides, diabetes or cancer. All catalog peptides are supplied for in-vitro and approved animal research only.