Peptide science terminology.

Agonist

A molecule that binds a receptor and activates it to produce a biological response.

Allosteric modulator

A ligand that binds a receptor site distinct from the orthosteric (primary) site, altering receptor response without directly activating it.

AMPK

AMP-activated protein kinase — a cellular energy sensor activated by low ATP:AMP ratio. Target of metformin and MOTS-c.

Amino acid

Organic molecule containing an amine and carboxyl group; the monomer of peptides and proteins. 20 standard residues in human biology.

BDNF

Brain-derived neurotrophic factor — a neurotrophin that supports neuronal survival, plasticity and LTP. Upregulated by Semax and exercise.

Bioavailability

The fraction of an administered dose that reaches systemic circulation. Peptides typically have low oral bioavailability due to GI proteolysis.

BPC-157

Body Protection Compound 157 — a 15-amino-acid pentadecapeptide derived from gastric juice, studied for tissue-repair and cytoprotective effects.

Cardiolipin

A unique phospholipid found exclusively in the inner mitochondrial membrane; binding target of SS-31 (elamipretide).

cAMP

Cyclic adenosine monophosphate — second messenger produced by adenylyl cyclase following Gαs-coupled GPCR activation.

CJC-1295

A GHRH analogue with substitutions improving half-life. The DAC variant binds albumin covalently for ~8-day half-life.

COA (Certificate of Analysis)

A document from a manufacturer detailing purity, identity, and quality testing for a specific lot of a chemical product.

Epitope

The portion of an antigen that is recognised by an antibody or T-cell receptor.

GHRH

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

GHRP

Growth-hormone-releasing peptide — synthetic peptides (e.g. GHRP-2, GHRP-6, ipamorelin, hexarelin) that activate the ghrelin/GHS-R1a receptor.

GLP-1

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

GPCR

G-protein coupled receptor — a seven-transmembrane receptor family that transduces extracellular signals via heterotrimeric G-proteins. ~34% of FDA-approved drugs target GPCRs.

Half-life (t½)

The time required for the plasma concentration of a substance to decrease by half.

HPLC

High-performance liquid chromatography — the standard analytical method for assessing peptide purity (typically reverse-phase C18).

IGF-1

Insulin-like growth factor 1 — hepatically produced in response to GH; mediates many anabolic actions of growth hormone.

Incretin

Class of metabolic hormones (GLP-1, GIP) released after eating that stimulate insulin secretion.

Lyophilisation

Freeze-drying — process used to preserve peptides as stable, water-free powders for long-term storage.

MC4R

Melanocortin-4 receptor — GPCR in the hypothalamic PVN involved in appetite, energy balance and sexual-arousal pathways.

MOTS-c

A 16-amino-acid mitochondrial-derived peptide encoded within the mtDNA 12S rRNA gene; activates AMPK and improves insulin sensitivity.

Pharmacokinetics (PK)

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

Pharmacodynamics (PD)

Study of what a drug does to the body — receptor binding, signalling and biological response.

Pulsatile secretion

Hormonal release in discrete bursts rather than continuously; characteristic of physiological GH, GnRH and ACTH.

Receptor agonism

Activation of a receptor by a ligand to produce a downstream biological effect.

Receptor antagonism

Blockade of receptor activity by a ligand that binds without activating it.

Selectivity

The relative affinity of a ligand for one receptor or subtype over others.

SPPS

Solid-phase peptide synthesis — Merrifield's method (1963) for stepwise peptide chain assembly on an insoluble resin.

SS-31 (elamipretide)

A tetrapeptide that binds cardiolipin on the inner mitochondrial membrane, stabilising electron-transport-chain function.

TB-500

A synthetic 7-aa fragment (LKKTETQ) of thymosin β-4, studied for endothelial migration and tissue repair.

Thymosin α-1

A 28-aa immunomodulatory peptide that promotes T-cell maturation via TLR9 signalling. Licensed in many countries for hepatitis B.

VEGFR

Vascular endothelial growth factor receptor — tyrosine kinase receptor driving angiogenesis; upregulated by BPC-157 in preclinical models.