The peptide science A–Z.

A ligand that binds a receptor and activates downstream signalling.

A ligand that binds at a site distinct from the receptor's primary (orthosteric) site, altering activity.

Organic molecules containing an amine group, a carboxyl group and a unique side chain (R-group). The monomers of peptides.

A ligand that occupies a receptor without activating it, blocking endogenous ligand binding.

Lot-specific analytical testing (identity, purity, water content, endotoxin) performed before release.

Peptides that exert measurable biological effects through receptor binding, enzyme modulation or membrane interaction.

The fraction of a substance that reaches systemic circulation after administration.

Cyclic adenosine monophosphate — second messenger generated by adenylyl cyclase downstream of Gαs-coupled GPCRs.

The phospholipid bilayer that separates a cell from its environment and houses transmembrane receptors.

A batch-specific document detailing the identity, purity, appearance and analytical methods used to release a peptide lot.

A three-nucleotide sequence in mRNA that specifies one amino acid (or a stop signal).

A temperature-controlled supply chain (typically 2–8 °C or –20 °C) preserving peptide integrity from manufacture to laboratory.

Adrenal glucocorticoid steroid hormone that regulates stress response, metabolism and immunity.

Sulfur-containing amino acid that forms disulfide bridges between residues.

Secreted signalling proteins (IL-, IFN-, TNF-families) regulating immunity and inflammation.

The aqueous interior of a cell, excluding the nucleus, containing organelles and cytoskeleton.

The mirror-image stereoisomer of a natural L-amino acid.

A covalent S–S bond between two cysteine residues that locks tertiary structure.

Deoxyribonucleic acid — the double-helical molecule that stores genetic information in all known organisms.

Membrane network where secreted and membrane proteins are synthesised, folded and post-translationally modified.

Lipopolysaccharide fragments from Gram-negative bacterial cell walls; quantified by the LAL assay.

Nine amino acids the human body cannot synthesise and must obtain from diet: His, Ile, Leu, Lys, Met, Phe, Thr, Trp, Val.

The thermodynamically driven process by which a peptide or protein adopts its functional 3D structure.

Growth-hormone-releasing hormone — a 44-aa hypothalamic peptide that stimulates pituitary GH secretion.

Growth-hormone-releasing peptides — synthetic ghrelin/GHS-R1a agonists (ipamorelin, hexarelin, GHRP-2/6).

Glucose-dependent insulinotropic polypeptide — the second major incretin hormone, released by intestinal K-cells.

Glucagon-like peptide-1 — an incretin hormone from intestinal L-cells that potentiates glucose-dependent insulin secretion.

A 29-amino-acid pancreatic peptide that raises blood glucose by stimulating hepatic glycogenolysis.

The smallest amino acid (H side chain); achiral and highly flexible.

Stacked organelle that further modifies, sorts and packages proteins received from the ER.

G-protein coupled receptor — a seven-transmembrane receptor family transducing extracellular signals via heterotrimeric G-proteins.

Peptides that drive cell proliferation, differentiation and tissue repair (e.g. VEGF, FGF, IGF).

A 191-amino-acid pituitary peptide hormone that stimulates growth, lipolysis and IGF-1 release.

The time required for the plasma concentration of a compound to fall by half.

Chemical messengers secreted by endocrine glands that travel through blood to act on distant target tissues.

High-performance liquid chromatography — the gold-standard method for assessing peptide purity, usually with C18 reverse-phase columns and UV detection at 214 nm.

Insulin-like growth factor 1 — a hepatic peptide hormone mediating many anabolic actions of GH.

A class of gut peptide hormones (GLP-1, GIP) released after meals to enhance insulin secretion.

A 51-amino-acid pancreatic peptide hormone (A and B chains linked by disulfides) regulating glucose homeostasis.

Any molecule that binds a receptor — endogenous hormone, drug or research peptide.

Freeze-drying under vacuum to produce a stable, water-free powder.

An analytical technique that ionises a sample and measures its mass-to-charge ratio to confirm molecular identity.

Melanocortin-4 receptor — hypothalamic GPCR controlling appetite, energy balance and sexual arousal.

Pineal indoleamine hormone regulating circadian rhythm.

Double-membraned organelles that generate ATP via oxidative phosphorylation and host their own circular DNA.

Messenger RNA — a transcript that carries genetic information from the nucleus to the ribosome.

Membrane-bound organelle housing chromosomal DNA and the machinery for transcription.

A peptide containing fewer than ~10 amino acid residues.

A 9-amino-acid cyclic peptide hormone involved in social bonding, lactation and parturition.

A short chain of amino acids linked by peptide bonds, typically 2–50 residues long.

A covalent amide bond formed between the carboxyl group of one amino acid and the amino group of the next, releasing water.

Non-peptide or modified-peptide molecules engineered to mimic the active conformation of a natural peptide.

Study of what a compound does to the body — receptor binding, signalling, downstream effects.

Study of what the body does to a compound — absorption, distribution, metabolism, excretion.

A chain of ~10–50 amino acids; longer chains fold into proteins.

A large biomolecule made of one or more polypeptide chains folded into a defined 3D structure.

The percentage of the desired peptide in a lyophilised product, typically measured by HPLC peak area.

A protein that recognises a specific ligand and transduces that binding into a cellular response.

The laboratory process of dissolving a lyophilised peptide in an appropriate solvent (typically bacteriostatic water).

Macromolecular complex of rRNA and proteins that translates mRNA into peptide chains.

Ribonucleic acid — a single-stranded nucleic acid that mediates information flow from DNA to protein.

The variable chemical group on each amino acid that defines its identity and properties.

Short N-terminal sequences (~15–30 aa) that direct a nascent protein to the endoplasmic reticulum or other compartments.

A cyclic peptide hormone that inhibits GH and TSH release.

Solid-phase peptide synthesis — Merrifield's 1963 stepwise assembly of peptide chains on insoluble resin.

How long a peptide retains structural integrity and activity under defined storage conditions.

Absence of viable microbial contamination, tested by membrane filtration or direct inoculation methods.

Recommended laboratory conditions for long-term peptide preservation — typically lyophilised at –20 °C, protected from light.

Peptides assembled chemically (typically by solid-phase peptide synthesis) rather than ribosomally.

Synthesis of an RNA copy from a DNA template by RNA polymerase.

Ribosomal synthesis of a polypeptide from an mRNA template.

Formal demonstration that an analytical method consistently produces results meeting predetermined specifications.