● GLOSSARY80 TERMS · DEFINED

The glossary.

80 definitions spanning pharmacology, research methods, regulatory terms, and practical peptide science.

Key terms used in peptide science and research — the jargon you’ll run into across profiles, forum threads, and the primary literature. Jump to a letter, or scroll.

§ A

9 terms

Absorption: Movement of a substance from its site of administration into the bloodstream or local tissue compartment.
Acetylation: Addition of an acetyl group to a molecule. In peptides, N-terminal acetylation can change stability, charge, or receptor interaction.
Agonist: A ligand that binds to a receptor and activates signaling through that receptor.
Amidation: Conversion of a peptide's carboxyl terminus to an amide. C-terminal amidation occurs naturally in many peptide hormones and can affect stability or activity.
Amino Acid: An organic molecule with amino and carboxyl groups. Amino acids are the building blocks linked together to form peptides and proteins.
Amphipathic: Having both water-attracting and water-repelling regions. Amphipathic structure is common in peptides that interact with membranes.
Analog: A modified version of a natural molecule designed to retain some shared structural or functional features.
Antagonist: A ligand that binds to a receptor without activating it and reduces or blocks activation by other ligands.
AUC: Area under the concentration-time curve. A pharmacokinetic measure of total systemic exposure to a substance over time.

§ B

3 terms

Bacteriostatic Water: Sterile water that contains a bacteriostatic preservative, commonly benzyl alcohol, to limit bacterial growth after the container is opened.
Bioavailability: The fraction of an administered substance that reaches systemic circulation in unchanged or active form.
Bioregulator: A term used for short regulatory peptides proposed to influence cellular processes. The term is used differently across research and commercial contexts.

§ C

8 terms

C-Terminal: The end of a peptide or protein chain with a free carboxyl group. Peptide sequences are conventionally written from N-terminal to C-terminal.
CAS Number: A unique Chemical Abstracts Service registry identifier assigned to a chemical substance.
Certificate of Analysis: A document reporting analytical test results for a material, such as identity, purity, concentration, or contaminant testing.
Clearance: The pharmacokinetic process by which a substance is removed from plasma, often through metabolism, renal elimination, or biliary elimination.
Clinical Trial: A research study in humans designed to evaluate safety, pharmacology, or clinical outcomes under a defined protocol.
Compounding Pharmacy: A pharmacy that prepares customized medications under applicable regulatory rules. In the United States, 503A and 503B facilities operate under different frameworks.
Concentration: The amount of a substance present in a given volume or mass, commonly expressed as mass per volume or molarity.
Cyclization: Formation of a ring structure in a peptide, often through a bond between side chains or between terminal groups.

§ D

5 terms

Dalton: A unit of molecular mass approximately equal to one atomic mass unit. Peptide and protein masses are often reported in daltons or kilodaltons.
Degradation: Chemical or enzymatic breakdown of a peptide into smaller fragments or amino acids.
Desensitization: Reduced receptor responsiveness after repeated or sustained receptor activation.
Disulfide Bond: A covalent bond between two cysteine residues. Disulfide bonds help stabilize the folded structures of some peptides and proteins.
Dose-Response Curve: A graph showing the relationship between dose or concentration and a measured biological response in a defined experimental setting.

§ E

2 terms

Endogenous: Produced within the body rather than introduced from an external source.
Exogenous: Originating outside the body and introduced from an external source.

§ F

2 terms

First-Pass Metabolism: Metabolism that occurs in the gut wall or liver before an orally absorbed substance reaches systemic circulation.
Formulation: The complete preparation of an active substance with excipients, solvent, buffer, or delivery system.

§ G

10 terms

Gastric Emptying: The movement of stomach contents into the small intestine. Several gut hormones can influence the rate of this process.
GH: Growth hormone, a peptide hormone released by the anterior pituitary that participates in growth, metabolism, and endocrine signaling.
Ghrelin: A peptide hormone produced mainly in the stomach that binds the growth hormone secretagogue receptor and participates in hunger and endocrine signaling.
GHRH: Growth hormone-releasing hormone, a hypothalamic peptide that stimulates growth hormone synthesis and release from the pituitary.
GHRP: Growth hormone-releasing peptide. A research term for synthetic peptides that activate the growth hormone secretagogue receptor.
GIP: Glucose-dependent insulinotropic polypeptide, an incretin hormone released from the small intestine after nutrient intake.
GLP-1: Glucagon-like peptide-1, an incretin hormone released from intestinal L cells that participates in glucose-dependent insulin secretion, glucagon regulation, gastric emptying, and appetite signaling.
GLP-1 Receptor Agonist: A ligand that activates the GLP-1 receptor. This drug class includes approved medications and investigational molecules studied for metabolic indications.
Glucagon: A peptide hormone released by pancreatic alpha cells that helps regulate blood glucose, partly by signaling the liver to release glucose.
Glucagon Receptor Agonist: A ligand that activates the glucagon receptor. Some multi-receptor metabolic peptides are designed to include glucagon receptor activity.

§ H

6 terms

Half-life: The time required for the amount or concentration of a substance to decrease by 50% under specified conditions.
Hormone: A signaling molecule produced by one tissue and transported to act on cells elsewhere in the body.
HPG Axis: The hypothalamic-pituitary-gonadal axis, an endocrine feedback system involving gonadotropin-releasing hormone, luteinizing hormone, follicle-stimulating hormone, and sex steroids.
HPLC: High-performance liquid chromatography, an analytical method used to separate and quantify components in a sample.
Hydrophilic: Having affinity for water or polar environments.
Hydrophobic: Having low affinity for water and greater affinity for nonpolar environments such as lipid membranes.

§ I

6 terms

IGF-1: Insulin-like growth factor 1, a peptide hormone involved in growth and metabolism. It is regulated by growth hormone and nutritional state.
Immunogenicity: The ability of a substance to provoke an immune response, including antibody formation.
In Vitro: Performed outside a living organism, such as in cell culture, biochemical assays, or test tubes.
In Vivo: Performed in a living organism, such as an animal model or human study.
Incretin: A gut-derived hormone that enhances glucose-dependent insulin secretion after nutrient intake. GLP-1 and GIP are the main human incretins.
Investigational New Drug: A regulatory application that permits clinical testing of an investigational drug in humans in the United States.

§ L

3 terms

Ligand: A molecule that binds to a target, such as a receptor, enzyme, transporter, or binding protein.
Lipophilicity: The tendency of a molecule to partition into fats or nonpolar environments. Lipophilicity can influence distribution, membrane interaction, and formulation.
Lyophilization: Freeze-drying, a process that removes water from a frozen material under vacuum to create a dry solid.

§ M

3 terms

Melanocortin Receptor: A family of G protein-coupled receptors that bind melanocortin peptides and participate in pigmentation, adrenal, appetite, and sexual function pathways.
Metabolite: A product formed when a substance is chemically changed by enzymes or other biological processes.
Molecular Weight: The mass of a molecule, commonly reported in daltons for peptides and proteins.

§ N

2 terms

N-Terminal: The end of a peptide or protein chain with a free amino group. It is the starting end when sequences are written conventionally.
Neuropeptide: A peptide used by neurons or neuroendocrine cells for signaling, modulation, or hormone-like communication.

§ P

13 terms

Paracrine Signaling: Cell signaling in which a molecule acts on nearby cells rather than traveling through the bloodstream to distant tissues.
Peptidase: An enzyme that breaks peptide bonds and degrades peptides or proteins.
Peptide: A chain of amino acids linked by peptide bonds. Peptides are generally shorter than proteins, though the boundary is conventional rather than absolute.
Peptide Bond: The amide bond connecting the carboxyl group of one amino acid to the amino group of another.
Peptide vs Small Molecule: A peptide is an amino-acid chain with peptide bonds, while a small molecule is usually a lower-mass organic compound with a non-polymeric structure.
Pharmacodynamics: The study of what a substance does to the body, including target binding, mechanism of action, and concentration-response relationships.
Pharmacokinetics: The study of how the body handles a substance, including absorption, distribution, metabolism, and excretion.
Placebo-Controlled: A study design in which results in an active-treatment group are compared with results in a group receiving an inactive control.
Plasma Protein Binding: The reversible binding of a substance to proteins in blood plasma, which can affect distribution, free concentration, and clearance.
Preclinical: Research performed before human clinical testing, commonly including biochemical, cell, and animal studies.
Prodrug: A compound administered in an inactive or less active form that is converted in the body to an active drug.
Proteolysis: The enzymatic breakdown of proteins or peptides by cleavage of peptide bonds.
Purity: The proportion of the intended substance in a sample relative to impurities or related compounds, usually measured by analytical methods such as HPLC.

§ R

2 terms

Receptor: A protein that binds a signaling molecule and converts that binding event into a cellular response.
Reconstitution: The process of adding a solvent to a dry material to return it to a liquid preparation.

§ S

4 terms

Secretagogue: A substance that stimulates a cell or gland to secrete another substance, such as a hormone.
Selectivity: The preference of a ligand for one target over other possible targets.
Stability: The ability of a substance to retain its chemical identity, potency, and physical properties under defined storage or handling conditions.
Subcutaneous: Located under the skin. In pharmacology, subcutaneous administration places a substance into the tissue layer beneath the dermis.

§ T

2 terms

Tachyphylaxis: A rapid decrease in response after repeated or continuous exposure to a substance.
Titration: Stepwise adjustment of an amount or concentration in a defined protocol, often used in clinical and laboratory contexts.

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