Read About Peptides

What peptides are

A peptide is a short chain of amino acids joined by amide (peptide) bonds. The boundary with “protein” is a matter of convention rather than chemistry — chains up to roughly fifty residues are generally called peptides. Sequence determines nearly everything that follows: charge at a given pH, solubility, secondary structure, susceptibility to proteolysis, and how the molecule behaves on a chromatography column.

Modifications change that behaviour substantially. N-terminal acetylation and C-terminal amidation reduce charge at the termini and slow enzymatic degradation. Cyclisation constrains conformation, which usually raises receptor selectivity. Lipidation — attaching a fatty acid chain, as in several metabolic research compounds — dramatically alters solubility and protein binding. Two preparations with the same core sequence and different modifications are, for analytical purposes, different compounds.

Receptor mechanisms

Most peptides of research interest act as ligands at cell-surface receptors, commonly G protein-coupled receptors. Characterising that interaction in vitro typically involves several complementary measurements:

• Binding affinity — competitive displacement of a labelled reference ligand, reported as K_i or K_d.
• Selectivity — the same assay run across a receptor panel, since a compound that is potent but promiscuous is difficult to interpret.
• Functional response — second-messenger readouts such as cAMP accumulation or calcium flux, which distinguish agonists from antagonists.
• Dose-response — EC₅₀ or IC₅₀ derived from a concentration series, ideally with a reference agonist run in parallel on the same plate.

Results are only comparable when the cell line, expression level, buffer composition and incubation time are held constant. This is the main reason literature values for the same compound vary across publications.

How the catalog is organised

We group compounds by the research area in which they are most commonly cited, not by any claimed effect:

• Tissue repair studies — compounds used in cell migration, angiogenesis and matrix remodelling models.
• Metabolic studies — incretin and mitochondrial-derived peptides used in receptor pharmacology and energy metabolism work.
• Neuroscience studies — compounds used in neurotrophic factor expression, receptor binding and neuroprotection assays.
• Cellular aging studies — coenzymes and short peptides used in sirtuin, telomere and redox research.
• Secretagogue studies — GHRH analogues and ghrelin receptor ligands used as reference agonists in pituitary cell models.
• Dermal research — copper-binding and melanocortin compounds used in fibroblast and melanocyte culture.

Analytical methods

Five methods describe the material in your vial. Each answers a different question.

Reverse-phase HPLC

Separates components by hydrophobicity with UV detection at 215 nm, where the peptide backbone absorbs. Purity is the target peak area as a percentage of total peak area. This is the number usually quoted as “purity,” and it is meaningful only alongside the method: gradient, column and detection wavelength all shift the result.

LC-MS

Confirms identity by measuring molecular mass. Necessary because HPLC alone cannot distinguish the target from a closely related impurity that happens to co-elute — a deletion sequence missing a single residue, for instance.

Karl Fischer titration

Quantifies residual water after lyophilisation. Practically important: if a vial is 6% water by mass and that is not accounted for, every concentration calculated from a gravimetric measurement is systematically wrong by that margin.

LAL endotoxin assay

Measures bacterial endotoxin, a frequent confounder in cell-culture experiments. Endotoxin can produce inflammatory readouts entirely unrelated to the compound being studied.

ICP-MS

Screens for heavy metal carry-over from reagents, resins and hardware, which can inhibit enzymes and distort metal-dependent assays.

Handling and stability

Lyophilised peptides are comparatively stable but not inert. Three factors dominate degradation:

• Moisture. Water enables hydrolysis and deamidation. Let a vial reach room temperature before opening so condensation does not form on a cold cake.
• Temperature. Store sealed material at −20 °C. Solutions degrade far faster than solids; establish your own stability window rather than assuming one.
• Oxidation. Sequences containing methionine, cysteine or tryptophan are susceptible. Protect from light and minimise headspace exposure.

Mechanical stress matters too. Vortexing a reconstituted peptide can shear chains and promote aggregation; swirl gently instead. Aliquot before freezing, because repeated freeze-thaw cycles measurably shift the impurity profile.

Laboratory safety and scope

Treat every research chemical as having an incompletely characterised hazard profile. Gloves, eye protection and a lab coat are a minimum; weigh lyophilised powders in a manner that controls airborne dust. Maintain documentation linking each vial to its batch certificate, and dispose of material through your institutional chemical waste stream.

Further reading

Primary literature is the right starting point for any specific compound. PubMed and the published methods sections of peer-reviewed papers will describe assay conditions in far more detail than any supplier page can. Where a compound in our catalog is widely cited, the product page lists the documented research areas for orientation.