Reference entries on peptides, receptors, and pharmacology concepts.
The peptide Encyclopedia is a comprehensive reference covering every aspect of polydeoxyribonucleotide science — from molecular mechanisms and receptor pathways to formulation technology and regulatory standards. Each entry is peer-reviewed and regularly updated as new research emerges.
The peptide bond is the covalent amide link that joins amino acids into chains. Its planar, partially-double-bonded geometry dictates peptide folding and signaling.
Peptides are short chains of amino acids linked by peptide bonds. This entry covers the chemistry, classification, and why peptides sit at the center of a growing therapeutic landscape.
Key terms and definitions used across peptide science, skincare formulations, and regenerative medicine.
A G-protein-coupled receptor activated by adenosine. Several regenerative peptides and polynucleotides are thought to exert effects via A2A receptor signaling, including anti-inflammatory cytokine modulation and fibroblast activation.
A half-life-extension strategy where a peptide is engineered with a fatty acid or DAC chain that reversibly binds circulating albumin, slowing renal clearance. Used in semaglutide, tirzepatide, liraglutide, and CJC-1295 DAC.
5′ AMP-activated protein kinase — a cellular energy-sensing enzyme that switches on catabolic (fat-burning, glucose-uptake) pathways in low-energy states. MOTS-c and metformin both act at least partly through AMPK activation.
Sterile water containing 0.9% benzyl alcohol as a bacteriostatic preservative, enabling multi-dose use over 28 days. The standard diluent for peptide reconstitution.
Short peptides (often 2–4 amino acids) developed primarily in Russian gerontology research, proposed to modulate gene expression in specific tissues. Epitalon is the most-studied. Western regulatory recognition is limited.
A chemical modification that allows a peptide to covalently bind serum albumin, dramatically extending half-life. CJC-1295 with DAC has a multi-day half-life vs ~30 minutes without DAC.
Growth-hormone-releasing hormone — a 44-amino-acid hypothalamic peptide that stimulates anterior pituitary somatotrophs to release growth hormone. Synthetic GHRH analogs (CJC-1295, Tesamorelin, Sermorelin) extend GHRH's short native half-life.
Synthetic peptides that bind GHSR-1a to stimulate GH release. Includes GHRP-2, GHRP-6, Hexarelin, Ipamorelin. Ipamorelin is the most receptor-selective.
Growth-hormone secretagogue receptor — a G-protein-coupled receptor bound by endogenous ghrelin and by synthetic GHRP-class peptides like Ipamorelin, GHRP-6, and Hexarelin. Activation amplifies GHRH-driven GH release.
Glucose-dependent insulinotropic polypeptide — the other major incretin alongside GLP-1, released by intestinal K-cells. Tirzepatide agonizes both GIP and GLP-1 receptors.
Glucagon-like peptide-1 — a 30-amino-acid incretin hormone released by intestinal L-cells after meals. Stimulates glucose-dependent insulin secretion, suppresses glucagon, delays gastric emptying, and reduces appetite centrally.
The time required for the concentration of a peptide in circulation to drop by 50%. Semaglutide's ~7-day half-life permits weekly dosing; Sermorelin's ~15-minute half-life requires daily or more frequent dosing.
High-performance liquid chromatography — the standard analytical method for assessing peptide purity. Research-grade peptides are typically sold with a certificate of analysis (COA) showing HPLC purity ≥95–98%.
Insulin-like growth factor 1 — the primary hepatic mediator of growth-hormone's anabolic actions. Serum IGF-1 is the most common biomarker for assessing GH-axis stimulation from GHRH analogs or GHRPs.
Injection directly into muscle tissue via a longer needle. Faster absorption than subcutaneous but more painful and rarely required for peptide protocols.
Abnormal distribution of body fat — can be visceral (belly-dominant, as in HIV lipodystrophy treated with Tesamorelin) or local (caused by repeat-site injections of insulin or peptides).
Freeze-drying — the process of removing water from a frozen peptide solution under vacuum, producing a stable powder. Lyophilized peptides are shelf-stable for years and require reconstitution with bacteriostatic water before use.
The melanocortin receptor on melanocytes responsible for tanning response. MC1R activation by melanotan-I and melanotan-II drives melanogenesis; PT-141 has MC1R activity as a mild side effect.
A G-protein-coupled receptor in the hypothalamus central to appetite and sexual-arousal regulation. PT-141 (bremelanotide) acts primarily through MC4R; setmelanotide is FDA-approved for MC4R-pathway obesity.
A signaling peptide synthesized inside mitochondria that acts systemically. MOTS-c is the prototype, encoded in mitochondrial 12S rRNA.
A mesotherapy injection pattern of many small, shallow intradermal punctures across a treatment area. Used for polynucleotide skin boosters and some cosmetic peptide applications.
The covalent amide linkage between the carboxyl group of one amino acid and the amino group of the next, releasing a water molecule. The peptide bond is planar and partially double-bonded, restricting rotation and defining secondary structure.
The physiological pattern of hormone secretion in discrete pulses rather than tonic levels. GH is released in nocturnal and exercise-driven pulses; preserving this pattern is why GHRH analogs are preferred over recombinant GH for some applications.
The process of dissolving a lyophilized peptide in bacteriostatic water to create an injectable solution. Reconstitution technique (gentle swirl, not shake) and solvent volume determine peptide stability and per-unit concentration.
The hypothalamic counter-hormone to GHRH — suppresses GH release. Pulsatile GHRH agonism preserves somatostatin feedback; continuous rhGH dosing can disrupt it.
The anterior pituitary cell type that synthesizes and secretes growth hormone. Target cell for both GHRH analogs (via GHRH-R) and GHRPs (via GHSR-1a).
The standard chemistry for manufacturing synthetic peptides, developed by Bruce Merrifield (Nobel Prize 1984). Amino acids are added sequentially to a resin-anchored growing chain, enabling industrial-scale peptide production.
Administration into the fatty layer under the skin, typically via a 29–31 gauge insulin needle. The default route for most research and GLP-1 peptides because of predictable absorption and ease of self-administration.
A syringe calibrated so 100 units equals 1 mL. The standard tool for peptide self-administration because it permits precise measurement of small volumes.
Vascular endothelial growth factor receptor 2 — the primary receptor tyrosine kinase driving angiogenesis. BPC-157 appears to upregulate VEGFR2 expression, contributing to its pro-healing vascular effects in preclinical models.
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