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 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.

Endocrine signalling peptides released by glands and tissues to coordinate physiology — insulin, GH, GLP-1.

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.