Peptide vocabulary comes from four places at once: synthetic chemistry, analytical chemistry, formulation science and pharmacology. A certificate of analysis borrows from all four in a single page. This glossary collects fifty terms that recur on product pages, certificates and method sections. Definitions are short by design and framed for laboratory work.
How to use it
- Terms are grouped by context, not alphabetically.
- Where a term has a longer treatment on this site, the definition links to it.
- Everything is framed for a researcher handling a reagent.
Chemistry and structure
Amino acid. The building block of a peptide: an amino group, a carboxyl group and a distinguishing side chain. Twenty are genetically encoded, and synthetic peptides also use non-natural variants.
Residue. An amino acid once incorporated into a chain. It loses a water molecule in forming the bond, so it weighs slightly less than the free amino acid.
Sequence. The order of residues from the N-terminus to the C-terminus, written in one-letter or three-letter codes. Two peptides with the same composition in a different order are different compounds.
Tripeptide. A peptide of three residues, such as GHK. Short chains are simpler to synthesize and purify than long ones.
Molecular weight. The mass of one molecule in daltons. One dalton is roughly the mass of a hydrogen atom. Peptides run from a few hundred daltons to several thousand.
Molarity. Moles of solute per litre of solution. Converting a mass concentration to molarity needs the molecular weight and, for accurate work, the net peptide content.
Solubility. How readily the compound dissolves in a given solvent, driven by charge, hydrophobicity and pH. Lipidated peptides dissolve more slowly than short polar ones.
Lipidation. Attachment of a fatty acid chain, usually through a linker on a lysine side chain. In the published pharmacokinetic literature it promotes albumin binding and extends half-life, which is why compounds such as retatrutide carry a fatty diacid.
Oxidation. Addition of oxygen, most often at methionine, cysteine or tryptophan. Adds sixteen daltons per oxygen and shows as a separate chromatographic peak.
Deamidation. Conversion of an asparagine or glutamine side-chain amide to a carboxylic acid. Adds roughly one dalton and is common in solution.
Aggregation. Association of chains into dimers, oligomers or visible particles. Promoted by shaking, foaming, freeze-thaw and high concentration, and often irreversible.
Analytics and testing
HPLC. High-performance liquid chromatography, the standard method for separating a peptide sample into its components and reporting purity. Covered in HPLC purity explained.
Chromatogram. The output trace of a chromatographic run, plotting detector signal against time. One peak per resolved component, with the main peak sharp and symmetrical on a flat baseline.
Purity. The area of the main peak divided by the total area of all peaks. It describes composition among detected species and says nothing about identity.
Identity. Confirmation that the material is the compound named on the label. Established by mass spectrometry, not by chromatography.
Mass spectrometry. Measurement of the mass-to-charge ratio of ionized molecules. For peptides it is usually coupled to liquid chromatography and used to confirm identity.
Monoisotopic mass. The mass calculated from the lightest isotope of each element. Distinct from average mass, which weights isotopes by natural abundance and runs slightly higher.
Net peptide content. The fraction of the powder's mass that is peptide, with counter-ions, bound water and excipient making up the rest. See net peptide content versus purity.
TFA salt. The trifluoroacetate salt form in which most synthetic peptides are supplied. Carried over from purification, it pairs with basic residues and adds mass.
Endotoxin. Lipopolysaccharide from the outer membrane of Gram-negative bacteria. Biologically active at very low concentrations and invisible to a purity assay.
LAL. Limulus amebocyte lysate, the reagent used in the standard endotoxin assay. Results are reported in endotoxin units.
Sterility. Absence of viable microorganisms, demonstrated by a growth-based test. A separate question from purity and from endotoxin content.
Handling, storage and formats
Lyophilization. Freeze-drying. Water is frozen and removed by sublimation under vacuum, leaving a dry porous cake far more stable than solution. Described in what is lyophilization.
Reconstitution. Dissolving lyophilized powder in a diluent to make a working stock. A reconstitution kit supplies the diluent and consumables together.
Bacteriostatic. Inhibiting bacterial growth rather than killing bacteria. Bacteriostatic water contains 0.9 percent benzyl alcohol, which is what allows a vial to be drawn from repeatedly.
Aliquot. A measured portion of a stock transferred to its own container. Aliquoting before freezing avoids repeated freeze-thaw on one tube.
Cold chain. Unbroken temperature-controlled handling from supplier to bench. Lyophilized material tolerates brief ambient excursions far better than solution does.
Freeze-thaw. One cycle of freezing and thawing a solution. Each cycle concentrates solutes at the ice interface and promotes aggregation, so cycles are counted and limited.
Stability. The extent to which a material stays within specification over time. Always stated with a temperature, a container and a time.
Shelf life. The period the sealed product is expected to remain within specification under recommended storage. Distinct from the shorter usable window after reconstitution.
Excipient. A non-active component such as mannitol used as a bulking agent. When present it is declared, and it lowers net peptide content by design.
Blend. A product containing more than one peptide, with each component mass listed separately on the label and tracked separately in records.
Co-lyophilized. Two or more compounds dried together in one vial from a single solution. The components dissolve together on reconstitution.
Vial. The sealed glass container holding the cake. Type I borosilicate is standard because it resists leaching.
Stopper and crimp cap. The elastomeric closure seated in the vial neck and the aluminium ring crimped over it. A lyophilization stopper is slotted so vapour escapes during drying, then fully seated inside the chamber.
Quality documents and grades
COA. Certificate of analysis, a lot-specific test report listing identity, purity, appearance and, where run, net peptide content and contamination testing. Read it with this guide.
Lot number. The identifier tying a production batch to its certificate. Without it a certificate cannot be matched to the vial in hand.
RUO. Research use only. The material is supplied for laboratory research and is not for human or animal use, not a drug and not a diagnostic. See what research use only means.
GMP versus research grade. Good manufacturing practice describes a regulated production and documentation system. Research-grade material is made to an analytical specification and tested per lot, without that framework.
Research pharmacology
Receptor. A protein that binds a specific molecule and converts that binding into a cellular signal.
Agonist. A molecule that binds a receptor and activates it. A partial agonist gives a submaximal response, and an antagonist binds without activating.
Half-life. In pharmacokinetic models, the time for the concentration of a compound in a compartment to fall by half. A measured property, not a handling instruction.
Incretin. A gut-derived hormone released after nutrient intake that potentiates glucose-dependent insulin secretion. GLP-1 and GIP are the two principal incretins.
GLP-1. Glucagon-like peptide-1, the most studied incretin target, associated in preclinical models with glucose-dependent insulin release and reduced food intake.
GIP. Glucose-dependent insulinotropic polypeptide, the second incretin. Dual-agonist literature suggests its receptor contributes additively to energy-balance outcomes in animal models.
Glucagon receptor. The receptor for glucagon, associated with hepatic glucose output and, in triple-agonist research, with energy expenditure. Compared across compounds in this three-way comparison.
Secretagogue. A compound that causes a cell to release a stored substance, most often used here for growth hormone release in model systems.
GHRH. Growth hormone releasing hormone, the hypothalamic peptide acting on pituitary somatotrophs. Several research analogs are built on its sequence.
Ghrelin receptor. The growth hormone secretagogue receptor, a second pathway to growth hormone release alongside GHRH. Covered in growth hormone secretagogues explained.
Bioregulator. A class of very short peptides, often two to four residues, investigated for tissue-selective effects on gene expression.
The compounds these terms describe, from BPC-157 to retatrutide, are listed across the research peptide catalogue.
Frequently asked questions
Which two terms get confused most often?
Purity and net peptide content. Purity is a ratio of chromatographic peak areas. Net peptide content is a fraction of the powder's total weight.
Is research grade the same as low quality?
No. Research-grade material is made to an analytical specification and tested per lot for identity and purity. The difference from GMP material is the documentation system around production, not the analytical result.
Why are pharmacology terms defined so cautiously here?
Because each describes findings in cell models, rodent studies or the published literature. None of it describes what a Homegrown Peptides product does in a person.
References
- IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1984. Nomenclature and symbolism for amino acids and peptides. European Journal of Biochemistry.
- Merrifield RB. 1963. Solid phase peptide synthesis I: the synthesis of a tetrapeptide. Journal of the American Chemical Society.
- Carpenter JF, et al. 1997. Rational design of stable lyophilized protein formulations: some practical advice. Pharmaceutical Research.
- Aebersold R, Mann M. 2003. Mass spectrometry-based proteomics. Nature.
- Mant CT, et al. 2007. HPLC analysis and purification of peptides. Methods in Molecular Biology.
Research use only. Every definition here is written for laboratory work. Homegrown Peptides products are not for human or animal use, are not drugs, and are not intended to diagnose, treat, cure or prevent any disease. Nothing here is medical advice or a protocol.
