Comprehensive Peptide Glossary
This glossary contains over 200 terms relevant to peptide biology, pharmacology, chemistry, and clinical science. Terms are organized alphabetically with category tags, definitions, and cross-references to learn pages and related terms.
ADME Pharmacology. Absorption, Distribution, Metabolism, Excretion — the four pillars of pharmacokinetics describing how a drug moves through the body. Related: pharmacokinetics, clearance, bioavailability. See: Pharmacology
Agonist Pharmacology. A molecule that binds a receptor and activates it, producing a biological response. Full agonists produce maximum response; partial agonists produce submaximal response. Related: antagonist, inverse agonist, receptor binding. See: Receptors
Albumin Binding Pharmacology. Non-covalent association of a drug with serum albumin, reducing free drug concentration and extending half-life. Example: CJC-1295-DAC uses covalent albumin binding (DAC) for half-life extension. Related: DAC, half-life, volume of distribution. See: CJC-1295 DAC vs No-DAC
Aldosterone Biology. Mineralocorticoid steroid hormone produced by adrenal zona glomerulosa. Regulates sodium/potassium balance and blood pressure. GHSR1a agonists (GHRP-6) stimulate aldosterone release. Related: ACTH, cortisol, GHSR1a. See: Receptors
Alpha-Melanocyte-Stimulating Hormone (α-MSH) Biology. Peptide hormone derived from POMC. Activates MC1R (pigmentation), MC3R, MC4R (appetite, energy homeostasis). Bremelanotide and melanotan peptides are synthetic analogs. Related: MC1R, MC3R, MC4R, bremelanotide, melanotan. See: Receptors
Amino Acid Chemistry. Organic molecule containing both amino (−NH₂) and carboxyl (−COOH) groups. 20 standard amino acids are protein building blocks. Classified by side chain: hydrophobic, polar, charged. Related: peptide bond, protein structure, zwitterion. See: Amino Acids
Amino Acid Properties Chemistry. Physical and chemical characteristics of amino acids: pKa, hydrophobicity, size, charge, hydrogen bonding capacity. Critical for predicting peptide structure and function. Related: pI, hydrophobicity, charge. See: Amino Acid Properties
Amylin (IAPP) Biology. Islet amyloid polypeptide, co-secreted with insulin from pancreatic β-cells. Regulates gastric emptying, glucagon secretion, satiety. Pramlintide is a synthetic analog. Related: insulin, GLP-1, gastric emptying. See: Therapeutic Peptides
Anabolic Steroid Pharmacology. Synthetic derivatives of testosterone that promote muscle growth (anabolism) and virilization (androgenicity). Examples: nandrolone, oxandrolone, stanozolol. Related: testosterone, androgen receptor, SARM. See: Testosterone vs GHRP-6
Angiotensin-Converting Enzyme (ACE) Biology. Dipeptidyl carboxypeptidase that converts angiotensin I to angiotensin II. ACE inhibitors are antihypertensive drugs. Related: angiotensin, bradykinin, ACE inhibitor. See: Therapeutic Peptides
Antagonist Pharmacology. A molecule that binds a receptor without activating it, blocking agonist effects. Competitive antagonists compete for the binding site; non-competitive antagonists bind allosterically. Related: agonist, inverse agonist, receptor binding. See: Receptors
Antimicrobial Peptide (AMP) Biology. Short peptides (5–50 aa) that kill microorganisms through membrane disruption. Part of innate immunity. Examples: defensins, cathelicidins, magainins. Related: innate immunity, membrane disruption. See: Therapeutic Peptides
Antithrombin III (ATIII) Biology. Serine protease inhibitor (serpin) that inactivates thrombin and factors Xa, IXa, XIa, XIIa. Heparin and enoxaparin enhance ATIII activity. Related: heparin, enoxaparin, thrombin. See: Heparin vs Enoxaparin
Aromatase (CYP19A1) Biology. Cytochrome P450 enzyme that converts testosterone to estradiol. Expressed in adipose tissue, brain, bone, and gonads. Inhibitors (anastrozole, letrozole) are used in breast cancer. Related: testosterone, estradiol, CYP450. See: Testosterone vs GHRP-6
Bioavailability (F) Pharmacology. Fraction of administered drug that reaches systemic circulation. Oral bioavailability (F) = (AUC_oral / AUC_IV) × (Dose_IV / Dose_oral). Related: AUC, first-pass metabolism, Cmax. See: Pharmacology
Bispecific Antibody Clinical. Engineered antibody that binds two different antigens simultaneously. Example: blinatumomab (CD19 × CD3). Related: monoclonal antibody, antibody-drug conjugate. See: Drug Pipeline
Blood-Brain Barrier (BBB) Biology. Semipermeable membrane barrier separating circulating blood from brain extracellular fluid. Composed of endothelial cells with tight junctions, astrocyte foot processes, and pericytes. Peptide crossing varies by size, charge, and lipophilicity. Related: CNS penetration, tight junctions. See: Drug Delivery
BMP (Bone Morphogenetic Protein) Biology. TGF-β superfamily member involved in bone and cartilage formation. BMP-2 and BMP-7 are used clinically for bone repair. Related: TGF-β, Wnt signaling. See: Signaling
Body Protection Compound (BPC) Pharmacology. Synthetic peptide derived from human gastric juice. BPC-157 (15 aa) demonstrates tissue-protective and regenerative properties across multiple organ systems. Related: GI protection, angiogenesis, NO system. See: BPC-157 Oral vs Injectable
Calcitonin Biology. 32-amino acid peptide hormone produced by thyroid C-cells. Inhibits osteoclast activity, reduces serum calcium. Synthetic salmon calcitonin (Miacalcin) is used for osteoporosis. Related: PTH, calcium homeostasis, bone metabolism. See: Therapeutic Peptides
Calcitonin Gene-Related Peptide (CGRP) Biology. 37-amino acid neuropeptide produced by alternative splicing of calcitonin gene. Potent vasodilator. CGRP antagonists (gepants) are used for migraine treatment. Related: migraine, vasodilation, sensory neurons. See: Therapeutic Peptides
Calcium-Sensing Receptor (CaSR) Biology. G-protein-coupled receptor that senses extracellular calcium levels. Expressed in parathyroid, kidney, bone. Cinacalcet is an allosteric modulator. Related: PTH, calcitonin, calcium homeostasis. See: Receptors
cAMP (Cyclic Adenosine Monophosphate) Biology. Second messenger generated by adenylyl cyclase from ATP. Activates protein kinase A (PKA). Central to GHRH, GH secretagogue, and many GPCR signaling pathways. Related: PKA, Gs protein, second messenger. See: Signaling
Carfilzomib Clinical. Irreversible proteasome inhibitor (epoxyketone). Used for multiple myeloma. Synthetic peptide derivative. Related: bortezomib, proteasome, cancer therapy. See: Drug Pipeline
Cell-Penetrating Peptide (CPP) Chemistry. Short peptides (5–30 aa) that facilitate cellular uptake of cargo. Examples: TAT, penetratin, transportan. Mechanism: endocytosis or direct membrane translocation. Related: drug delivery, endocytosis, membrane translocation. See: Drug Delivery
CGRP Antagonist (Gepant) Pharmacology. Small-molecule or peptide antagonist of CGRP receptor. Used for acute migraine treatment. Examples: ubrogepant, rimegepant, atogepant. Related: CGRP, migraine, receptor antagonist. See: Therapeutic Peptides
Cholecystokinin (CCK) Biology. Peptide hormone released by I-cells in duodenum. Stimulates pancreatic enzyme secretion, gallbladder contraction, satiety. CCK-8 (octapeptide) is the most active form. Related: pancreatic secretion, satiety, GI hormones. See: Signaling
Chromogranin A Biology. Acidic protein co-stored and co-secreted with hormones from neuroendocrine granules. Biomarker for neuroendocrine tumors. Related: neuroendocrine, biomarker, secretory granules. See: Clinical Trials
Clinical Trial Phases Clinical. Sequential stages of drug development: Phase I (safety, 20–100 subjects), Phase II (efficacy, 100–300), Phase III (confirmatory, 1000–3000), Phase IV (post-marketing). Related: FDA approval, EMA, regulatory. See: Clinical Trials
Cmax Pharmacology. Maximum plasma concentration achieved after drug administration. Key pharmacokinetic parameter indicating peak drug exposure. Related: Tmax, AUC, bioavailability. See: Pharmacology
Collagen Biology. Triple-helical structural protein providing tensile strength. Types I–XXVIII. Type I (skin, bone, tendon), type II (cartilage), type III (blood vessels, skin). Related: elastin, hydroxyproline, triple helix. See: Collagen vs Elastin
Complement System Biology. Part of innate immunity comprising ~30 proteins. Three pathways: classical, alternative, lectin. C3, C5 are central components. Related: innate immunity, inflammation. See: Signaling
Corticotropin-Releasing Hormone (CRH) Biology. 41-amino acid hypothalamic peptide. Stimulates ACTH release from anterior pituitary. Key mediator of stress response. Related: ACTH, HPA axis, cortisol. See: Receptors
Cortisol Biology. Glucocorticoid steroid hormone produced by adrenal zona fasciculata. Regulates metabolism, immune function, stress response. Elevated by GH secretagogues (GHRP-6). Related: ACTH, CRH, HPA axis, GHSR1a. See: Testosterone vs GHRP-6
CYP450 (Cytochrome P450) Biology. Family of heme-containing monooxygenases responsible for Phase I drug metabolism. Key isoforms: CYP3A4 (most drugs), CYP2D6, CYP2C9, CYP2C19, CYP1A2. Related: Phase I metabolism, first-pass effect, drug interactions. See: Peptide Interactions
Cysteine Chemistry. Amino acid with thiol (−SH) side chain. Forms disulfide bonds (Cys-Cys) critical for protein tertiary structure. Molecular weight: 121.16 Da. Related: disulfide bond, oxidation, reducing agent. See: Amino Acids
Cytotoxic T-Lymphocyte-Associated Antigen 4 (CTLA-4) Biology. Inhibitory receptor on T-cells that downregulates immune response. Ipilimumab is anti-CTLA-4 checkpoint inhibitor. Related: PD-1, checkpoint inhibitor, immunotherapy. See: Therapeutic Peptides
DAC (Drug Affinity Complex) Pharmacology. Synthetic moiety conjugated to peptides to enable covalent binding to serum albumin, dramatically extending half-life. Example: CJC-1295-DAC (6–8 day half-life vs 30 min without DAC). Related: albumin binding, half-life, CJC-1295. See: CJC-1295 DAC vs No-DAC
Defensin Biology. Antimicrobial peptide (29–35 aa) with 6 cysteine residues forming 3 disulfide bonds. α-defensins (neutrophils, Paneth cells), β-defensins (epithelial cells). Related: AMP, innate immunity. See: Therapeutic Peptides
Degarelix Clinical. GnRH receptor antagonist (dekapeptide). Used for advanced prostate cancer. Blocks LH/FSH release, reducing testosterone to castrate levels. Related: GnRH, leuprolide, prostate cancer. See: Therapeutic Peptides
Desmosine Chemistry. Unique cross-link amino acid formed from 4 lysine residues in elastin. Not found in collagen. Biomarker for elastin degradation. Related: elastin, cross-linking, isodesmosine. See: Collagen vs Elastin
Dipeptidyl Peptidase-4 (DPP-4) Biology. Serine protease that cleaves N-terminal dipeptides from proteins. Inactivates GLP-1 and GIP. DPP-4 inhibitors (sitagliptin) extend incretin half-life. Related: GLP-1, incretin, GIP. See: Signaling
Disulfide Bond Chemistry. Covalent bond between two cysteine residues (−S−S−). Stabilizes protein tertiary and quaternary structure. Reduced by DTT, β-mercaptoethanol; oxidized by glutathione. Related: cysteine, protein folding, redox. See: Structure
Dose-Response Relationship Pharmacology. Quantitative relationship between drug dose and biological response. Characterized by EC₅₀ (potency), E₅₀ (efficacy), and Hill coefficient (cooperativity). Related: EC₅₀, E₅₀, therapeutic window. See: Pharmacology
DPP-IV Resistance Pharmacology. Resistance to degradation by dipeptidyl peptidase-4, achieved through D-amino acid substitutions (e.g., D-Ala² in CJC-1295, semaglutide). Extends peptide half-life. Related: DPP-4, half-life, D-amino acid. See: Peptide Half-Life
Drug Delivery Pharmacology. Methods and systems for transporting therapeutic agents to target sites. Includes: injection, transdermal, oral, inhalation, nanoparticle, liposome, antibody-drug conjugate. Related: bioavailability, nanocarrier, liposome. See: Drug Delivery
Drug Pipeline Clinical. Sequential stages of drug development from discovery through approval. Related: clinical trials, regulatory approval. See: Peptide Drug Pipeline
EC₅₀ Pharmacology. Concentration producing 50% of maximum response. Measure of potency (lower EC₅₀ = higher potency). Related: E₅₀, dose-response, Hill equation. See: Pharmacology
Elastin Biology. Amorphous random-coil structural protein providing elastic recoil. Can stretch 150–200% and recover completely. Contains desmosine/isodesmosine cross-links. Related: collagen, tropoelastin, elastic fiber. See: Collagen vs Elastin
Enoxaparin Pharmacology. Low-molecular-weight heparin (LMWH). Average MW ~4,500 Da. Predominantly anti-Xa activity (anti-Xa:IIa ratio 2.7:1). No routine monitoring required. Related: heparin, ATIII, anti-Xa. See: Heparin vs Enoxaparin
Epitope Biology. Specific part of an antigen that is recognized by the immune system (antibody or T-cell receptor). Linear vs conformational epitopes. Related: antigen, antibody, MHC. See: Signaling
Estrogen Receptor (ER) Biology. Nuclear receptor activated by estradiol. ERα and ERβ subtypes with distinct tissue expression. Mediates reproductive, bone, cardiovascular effects. Related: estradiol, SERM, aromatase. See: Receptors
Exenatide Clinical. First-in-class GLP-1 receptor agonist (exendin-4 analog, 39 aa). Derived from Gila monster venom. Twice-daily SC injection. Related: GLP-1, semaglutide, liraglutide. See: Therapeutic Peptides
Fasting State Pharmacology. Metabolic state after 8–12 hours without food intake. Characterized by low insulin, high glucagon, hepatic glucose output. Important for pharmacokinetic study design. Related: postprandial, glucose homeostasis. See: Pharmacology
Favism Clinical. Hemolytic anemia caused by G6PD deficiency, triggered by fava beans or oxidative drugs. Illustrates importance of NADPH regeneration via pentose phosphate pathway. Related: G6PD, NADPH, hemolysis. See: NADH vs NADPH
Fibrinogen Biology. Plasma glycoprotein (340 kDa) converted to fibrin by thrombin during coagulation. Factor XIII cross-links fibrin polymers. Related: thrombin, coagulation cascade, factor XIII. See: Heparin vs Enoxaparin
First-Pass Metabolism Pharmacology. Hepatic and intestinal metabolism of orally administered drugs before reaching systemic circulation. Reduces oral bioavailability. Related: bioavailability, hepatic extraction, portal circulation. See: Pharmacology
Gastric Emptying Biology. Process of chyme movement from stomach to duodenum. Regulated by neural and hormonal factors. GLP-1 agonists delay gastric emptying, affecting drug absorption. Related: GLP-1, CCK, motilin. See: Peptide Interactions
Ghrelin Biology. 28-amino acid peptide hormone produced by gastric fundus. Only known endogenous ligand for GHSR1a. Stimulates GH release, appetite, and energy balance. Octanoylation at Ser3 is essential for activity. Related: GHSR1a, GH secretagogues, GHRP-6. See: Receptors
GHSR1a (Growth Hormone Secretagogue Receptor) Biology. Gq/Gs-coupled GPCR expressed in pituitary, hypothalamus, hippocampus, and other tissues. Activated by ghrelin and synthetic secretagogues (GHRP-6, ipamorelin, MK-677). Related: ghrelin, GHRP-6, cAMP, calcium signaling. See: Receptors
GLP-1 (Glucagon-Like Peptide-1) Biology. Incretin hormone produced by intestinal L-cells. Stimulates insulin secretion, suppresses glucagon, delays gastric emptying, promotes satiety. GLP-1 agonists (semaglutide, liraglutide) are used for diabetes and obesity. Related: incretin, GIP, DPP-4, semaglutide. See: Therapeutic Peptides
GLP-1 Receptor Agonist Pharmacology. Synthetic peptides that activate GLP-1R on pancreatic β-cells, hypothalamus, and other tissues. Include semaglutide, liraglutide, exenatide, dulaglutide. Related: GLP-1, incretin, diabetes, obesity. See: Semaglutide vs Tirzepatide
GnRH (Gonadotropin-Releasing Hormone) Biology. 10-amino acid decapeptide produced by hypothalamus. Stimulates LH and FSH release from anterior pituitary. Pulsatile release essential; continuous exposure causes downregulation. Related: LH, FSH, leuprolide, degarelix. See: Receptors
GnRH Agonist Pharmacology. Synthetic GnRH analogs (leuprolide, goserelin, triptorelin). Initial stimulation followed by desensitization and downregulation. Used for prostate cancer, endometriosis, precocious puberty. Related: GnRH, LH, FSH, castration. See: Therapeutic Peptides
GnRH Antagonist Pharmacology. Competitive GnRH receptor blockers (degarelix, cetrorelix, ganirelix). Immediate suppression of LH/FSH without initial flare. Used for prostate cancer, ovarian stimulation. Related: GnRH agonist, LH, FSH. See: Therapeutic Peptides
Growth Hormone (GH) Biology. 191-amino acid polypeptide hormone secreted by anterior pituitary somatotrophs. Stimulates IGF-1 production, lipolysis, protein synthesis. Pulsatile secretion pattern. Related: IGF-1, GHRH, GHSR1a, somatostatin. See: HGH vs IGF-1
Growth Hormone-Releasing Hormone (GHRH) Biology. 44-amino acid hypothalamic peptide. Stimulates GH release via GHRHR on somatotrophs. Sermorelin and CJC-1295 are synthetic analogs. Related: GHRHR, sermorelin, CJC-1295. See: Receptors
Guanine Nucleotide-Binding Protein (G-Protein) Biology. Heterotrimeric (α, β, γ) signal transducers coupled to GPCRs. Gs stimulates adenylyl cyclase; Gq activates phospholipase C; Gi inhibits adenylyl cyclase. Related: GPCR, cAMP, IP₃, second messenger. See: Signaling
Half-Life (t₁/₂) Pharmacology. Time for plasma concentration to decrease by 50%. Determined by clearance and volume of distribution: t₁/₂ = 0.693 × Vd / CL. Related: clearance, volume of distribution, steady state. See: Peptide Half-Life
Heparin Pharmacology. Sulfated glycosaminoglycan anticoagulant (MW 12,000–15,000 Da). Enhances ATIII activity (anti-Xa and anti-IIa). Requires aPTT monitoring. Reversible with protamine sulfate. Related: enoxaparin, ATIII, aPTT, protamine. See: Heparin vs Enoxaparin
Heparin-Induced Thrombocytopenia (HIT) Clinical. Immune-mediated adverse reaction to heparin. IgG antibody binds PF4-heparin complex, activating platelets. Type II (immune-mediated) is clinically significant. Related: heparin, PF4, thrombocytopenia. See: Heparin vs Enoxaparin
HGH (Human Growth Hormone) Pharmacology. Biosynthetic GH (somatropin) identical to endogenous human GH. Used for GH deficiency, Turner syndrome, wasting. Related: GH, IGF-1, somatostatin. See: HGH vs IGF-1
HMG-CoA Reductase Biology. Rate-limiting enzyme in cholesterol biosynthesis (mevalonate pathway). Statins are competitive inhibitors. Requires NADPH. Related: cholesterol, statins, NADPH. See: NADH vs NADPH
Human Serum Albumin (HSA) Biology. Most abundant plasma protein (35–50 g/L). Binds drugs, hormones, fatty acids. Target for DAC conjugation (CJC-1295-DAC binds Lys34). Related: DAC, albumin binding, pharmacokinetics. See: CJC-1295 DAC vs No-DAC
HPA Axis (Hypothalamic-Pituitary-Adrenal) Biology. Neuroendocrine system: CRH (hypothalamus) → ACTH (pituitary) → cortisol (adrenal). Regulates stress response, metabolism, immune function. Related: CRH, ACTH, cortisol. See: Signaling
Hydrolysis Chemistry. Chemical breakdown of a compound by reaction with water. Peptide bond hydrolysis catalyzed by proteases (pepsin, trypsin, chymotrypsin). Related: peptide bond, protease, proteolysis. See: Peptide Bonds
Hydroxyproline Chemistry. Modified amino acid (proline hydroxylated at C4). Stabilizes collagen triple helix through hydrogen bonding. Requires vitamin C for synthesis. Related: collagen, proline, vitamin C. See: Collagen vs Elastin
IGF-1 (Insulin-Like Growth Factor 1) Biology. 70-amino acid polypeptide with structural similarity to insulin. Produced primarily in liver under GH stimulation. Mediates many GH effects: growth, protein synthesis, cell proliferation. Related: GH, IGF-1R, insulin. See: HGH vs IGF-1
IGF-1 Receptor (IGF-1R) Biology. Transmembrane receptor tyrosine kinase. Activated by IGF-1. Stimulates PI3K/Akt and MAPK pathways. Overexpressed in many cancers. Related: IGF-1, insulin receptor, PI3K/Akt. See: Receptors
Incretin Biology. Gut hormones that potentiate insulin secretion after oral glucose. GLP-1 and GIP are primary incretins. DPP-4 degrades both. Related: GLP-1, GIP, DPP-4, insulin. See: Therapeutic Peptides
Insulin Biology. 51-amino acid heterodimeric peptide hormone (A-chain 21 aa, B-chain 30 aa, 2 interchain disulfide bonds). Produced by pancreatic β-cells. Lowers blood glucose via GLUT4 translocation, glycogen synthesis, lipogenesis. Related: GLP-1, IGF-1, glucose, GLUT4. See: Insulin Glargine vs Detemir
Insulin Glargine Pharmacology. Long-acting insulin analog (modified human insulin). Precipitates at injection site, forming microcrystals for slow dissolution. 24-hour duration. Related: insulin, insulin detemir, basal insulin. See: Insulin Glargine vs Detemir
Insulin Detemir Pharmacology. Long-acting insulin analog. Acylated with myristic acid, binds albumin for slow release. 12–18 hour duration. Related: insulin, insulin glargine, basal insulin. See: Insulin Glargine vs Detemir
Inverse Agonist Pharmacology. A molecule that binds a receptor and reduces its constitutive (basal) activity below the unliganded level. Opposite of agonist. Related: agonist, antagonist, constitutive activity. See: Receptors
Ipamorelin Pharmacology. Pentapeptide GHSR1a agonist (Aib-His-D-2Nal-D-Phe-Lys-NH₂). Selective GH secretagogue with minimal cortisol, prolactin, or aldosterone stimulation. Related: GHRP-6, GHSR1a, MK-677, CJC-1295. See: Ipamorelin vs MK-677
Kd (Dissociation Constant) Pharmacology. Concentration at which 50% of receptors are occupied. Lower Kd = higher binding affinity. Kd = k_off / k_on. Related: binding affinity, receptor occupancy, IC₅₀. See: Pharmacology
Kinase Biology. Enzyme that transfers phosphate groups from ATP to substrates (phosphorylation). Examples: PKA, PKC, PI3K, MAPK. Related: phosphorylation, signal transduction. See: Signaling
Leuprolide Clinical. GnRH agonist (9-amino acid). Used for prostate cancer, endometriosis, precocious puberty. Continuous administration causes castrate testosterone levels via receptor downregulation. Related: GnRH, prostate cancer, FSH, LH. See: Therapeutic Peptides
Liraglutide Clinical. Long-acting GLP-1 receptor agonist (97% homology to human GLP-1). Fatty acid acylation enables albumin binding. Once-daily SC injection. Used for diabetes and obesity. Related: GLP-1, semaglutide, DPP-4. See: Semaglutide vs Liraglutide
LMWH (Low-Molecular-Weight Heparin) Pharmacology. Heparin fragments (MW 2,000–8,000 Da) produced by controlled depolymerization. Predominantly anti-Xa activity. Predictable pharmacokinetics. Examples: enoxaparin, dalteparin, tinzaparin. Related: heparin, enoxaparin, anti-Xa. See: Heparin vs Enoxaparin
MC3R (Melanocortin-3 Receptor) Biology. Gs-coupled GPCR activated by α-MSH. Expressed in hypothalamus, gut. Regulates energy homeostasis, feeding behavior. Bremelanotide activates MC3R. Related: MC4R, α-MSH, bremelanotide. See: Receptors
MC4R (Melanocortin-4 Receptor) Biology. Gs-coupled GPCR activated by α-MSH. Expressed in hypothalamus. Central regulator of appetite and energy expenditure. MC4R mutations cause obesity. Bremelanotide activates MC4R for sexual dysfunction. Related: MC3R, α-MSH, bremelanotide, melanotan. See: Receptors
Mechanism of Action (MOA) Pharmacology. The specific biochemical interaction through which a drug produces its effect. Related: target, receptor, signaling pathway. See: Pharmacology
Melanotan I (Afamelanotide) Clinical. Synthetic α-MSH analog. Activates MC1R for photoprotection in erythropoietic protoporphyria. Approved in US and EU. Related: melanotan II, MC1R, α-MSH. See: Melanotan I vs Melanotan II
Melanotan II Pharmacology. Synthetic cyclic α-MSH analog. Activates MC3R and MC4R. Used experimentally for tanning, erectile dysfunction, obesity. Cross-reacts with MC1R (tanning) and MC4R (sexual function). Related: melanotan I, bremelanotide, PT-141. See: Melanotan I vs Melanotan II
Metabolic Clearance Rate (MCR) Pharmacology. Volume of plasma cleared of drug per unit time (mL/min). Inversely related to half-life for a given volume of distribution. Related: clearance, half-life, volume of distribution. See: Pharmacology
Metformin Clinical. Biguanide oral hypoglycemic. First-line treatment for type 2 diabetes. Reduces hepatic glucose production, increases insulin sensitivity. Does not cause hypoglycemia as monotherapy. Related: GLP-1, insulin, diabetes. See: Peptide Interactions
MK-677 (Ibutamoren) Pharmacology. Non-peptide GHSR1a agonist. Orally active GH secretagogue. Stimulates GH release with some cortisol elevation. Half-life ~4 hours. Related: GHRP-6, ipamorelin, GHSR1a. See: Ipamorelin vs MK-677
Monoclonal Antibody Clinical. Antibody produced by a single B-cell clone, recognizing one epitope. Examples: adalimumab (anti-TNF), trastuzumab (anti-HER2). Related: bispecific antibody, ADC, immunotherapy. See: Drug Pipeline
NAD⁺/NADH Biology. Nicotinamide adenine dinucleotide (oxidized/reduced forms). Primary electron carrier in catabolic metabolism (glycolysis, TCA cycle, β-oxidation). Donates electrons to ETC for ATP production. Related: NADPH, TCA cycle, oxidative phosphorylation. See: NADH vs NADPH
NADP⁺/NADPH Biology. Nicotinamide adenine dinucleotide phosphate (oxidized/reduced forms). Provides reducing equivalents for anabolic biosynthesis (fatty acid, cholesterol synthesis) and antioxidant defense (glutathione reduction). Related: NADH, pentose phosphate pathway, glutathione. See: NADH vs NADPH
Nebulizer Clinical. Device that converts liquid medication into fine aerosol mist for inhalation. Used for respiratory peptides (insulin, calcitonin). Related: inhalation, pulmonary delivery. See: Drug Delivery
Nociceptin Biology. 17-amino acid neuropeptide. Endogenous ligand for opioid receptor-like 1 (ORL-1) receptor. Involved in pain modulation, anxiety, feeding. Related: opioid, ORL-1. See: Receptors
Norepinephrine Biology. Catecholamine neurotransmitter and hormone. Sympathetic nervous system mediator. Regulates heart rate, blood pressure, alertness. Related: epinephrine, sympathetic, adrenal. See: Signaling
Obestatin Biology. 23-amino acid peptide derived from preproghrelin. Originally proposed as ghrelin antagonist, though this is debated. May regulate food intake and GI motility. Related: ghrelin, GHSR1a. See: Receptors
Oligopeptide Chemistry. Peptide containing 2–20 amino acid residues. Distinguished from dipeptides (2), tripeptides (3), and polypeptides (>20). Related: dipeptide, polypeptide, protein. See: Peptide Bonds
Oral Bioavailability Pharmacology. Fraction of orally administered drug reaching systemic circulation. Typically very low for peptides due to GI degradation and poor membrane permeability. Related: bioavailability, first-pass metabolism, GI stability. See: BPC-157 Oral vs Injectable
OT (Oxytocin) Biology. 9-amino acid cyclic neuropeptide. Produced by hypothalamus, released from posterior pituitary. Stimulates uterine contractions, milk ejection, social bonding. Related: vasopressin, social bonding. See: Oxytocin vs Vasopressin
Parathyroid Hormone (PTH) Biology. 84-amino acid peptide hormone produced by parathyroid glands. Regulates calcium homeostasis: increases serum calcium (bone resorption, renal reabsorption, intestinal absorption). Teriparatide (PTH 1-34) is used for osteoporosis. Related: calcitonin, calcium, bone metabolism. See: Therapeutic Peptides
Pentose Phosphate Pathway (PPP) Biology. Glucose metabolic pathway generating NADPH (for biosynthesis and glutathione reduction) and ribose-5-phosphate (for nucleotide synthesis). Rate-limiting enzyme: G6PD. Related: NADPH, G6PD, ribose. See: NADH vs NADPH
Peptide Chemistry. Short chain of amino acids linked by peptide bonds. Oligopeptides (2–20 aa), polypeptides (20–50 aa), proteins (>50 aa). Related: amino acid, peptide bond, protein. See: Peptide Bonds
Peptide Bond Chemistry. Amide bond (−CO−NH−) formed between amino acids by dehydration synthesis. Partial double-bond character (resonance) gives planar geometry. Related: peptide, protein, dehydration synthesis. See: Peptide Bonds
Peptide Calculator Tools. Online tool for calculating peptide molecular weight, reconstitution concentration, and dosing. Available at wikipept.com. Related: molecular weight, reconstitution. See: Calculations
Pharmacodynamics (PD) Pharmacology. Study of drug effects on the body (what the drug does). Includes receptor binding, dose-response relationships, therapeutic and adverse effects. Related: pharmacokinetics, dose-response, therapeutic index. See: Pharmacology
Pharmacokinetics (PK) Pharmacology. Study of what the body does to the drug. ADME: Absorption, Distribution, Metabolism, Excretion. Key parameters: t₁/₂, Cmax, Tmax, AUC, Vd, CL. Related: pharmacodynamics, ADME, clearance. See: Pharmacology
Phospholipase C (PLC) Biology. Enzyme that cleaves PIP₂ into IP₃ and DAG. IP₃ releases Ca²⁺ from ER; DAG activates PKC. Central to Gq-coupled receptor signaling. Related: IP₃, DAG, PKC, calcium. See: Signaling
PKA (Protein Kinase A) Biology. cAMP-dependent serine/threonine kinase. Activated by cAMP binding to regulatory subunits. Phosphorylates CREB, ion channels, metabolic enzymes. Related: cAMP, CREB, Gs protein. See: Signaling
PKC (Protein Kinase C) Biology. Serine/threonine kinase activated by DAG and Ca²⁺. Multiple isoforms with diverse functions: cell proliferation, differentiation, apoptosis. Related: DAG, PLC, calcium. See: Signaling
Prodrug Pharmacology. Inactive or less active compound that is metabolized to the active drug in vivo. Example: enalapril → enalaprilat. Related: metabolism, activation. See: Pharmacology
Progesterone Biology. C21 steroid hormone. Maintains endometrial lining, supports pregnancy, regulates menstrual cycle. Progestins are synthetic analogs. Related: estrogen, testosterone, adrenal. See: Receptors
Protease Biology. Enzyme that hydrolyzes peptide bonds. Classes: serine (trypsin), cysteine (caspase), metalloproteinase (MMP), aspartyl (pepsin). Related: peptide bond, proteolysis, degradation. See: Peptide Bonds
Proteasome Biology. Multi-catalytic protein complex that degrades ubiquitinated proteins. 20S core + 19S regulatory cap. Target of bortezomib and carfilzomib (cancer therapy). Related: ubiquitin, protein degradation, cancer therapy. See: Drug Pipeline
Protamine Sulfate Clinical. Positively charged protein that neutralizes heparin (negatively charged). 1 mg protamine neutralizes 100 units heparin. Partial reversal of enoxaparin. Related: heparin, enoxaparin, reversal. See: Heparin vs Enoxaparin
PT-141 (Bremelanotide) Pharmacology. Synthetic melanocortin analog (MC3R/MC4R agonist). Used for female sexual dysfunction (Vyleesi). Activates central melanocortin pathways for desire and arousal. Related: melanotan II, bremelanotide, MC4R. See: PT-141 vs Sildenafil
Purification Chemistry. Separation and isolation of target peptide from crude synthesis mixture. Methods: HPLC, ion-exchange, size-exclusion, affinity chromatography. Related: SPPS, HPLC, analytical. See: Purification Methods
QT Interval Clinical. Time from start of QRS complex to end of T wave on ECG. Represents ventricular depolarization and repolarization. Prolongation increases risk of torsades de pointes. Related: ECG, arrhythmia, drug safety. See: Peptide Interactions
Quality Control (QC) Chemistry. Analytical procedures to verify peptide identity, purity, and potency. Methods: HPLC, mass spectrometry, amino acid analysis, endotoxin testing. Related: HPLC, mass spec, purity. See: Purification
RANKL (Receptor Activator of NF-κB Ligand) Biology. TNF family member expressed on osteoblasts. Activates RANK on osteoclasts, stimulating bone resorption. Denosumab (anti-RANKL) inhibits osteoclast formation. Related: osteoclast, bone metabolism, osteoprotegerin. See: Signaling
Receptor Biology. Protein that binds a ligand (hormone, drug, neurotransmitter) and initiates a biological response. Types: ionotropic (ligand-gated ion channels), metabotropic (GPCRs), enzyme-linked (receptor tyrosine kinases). Related: agonist, antagonist, signaling. See: Receptors
Reconstitution Practical. Process of dissolving lyophilized peptide in a suitable solvent (typically bacteriostatic water or sterile water) for injection. Related: lyophilization, solubility, dosing. See: Reconstitution
Retatrutide Clinical. Triple agonist (GLP-1/GIP/glucagon receptor). Most potent weight loss agent in clinical trials. 24.2% weight loss at 48 weeks in Phase 2. Related: semaglutide, tirzepatide, GLP-1. See: Retatrutide vs Tirzepatide
Semaglutide Clinical. Long-acting GLP-1 receptor agonist. Weekly SC injection (Ozempic) or oral tablet (Rybelsus). 30% amino acid homology to exendin-4. C8 fatty acid chain enables albumin binding. Related: GLP-1, liraglutide, tirzepatide. See: Semaglutide vs Tirzepatide
Sermorelin Clinical. Synthetic GHRH(1-29) analog. Shortest biologically active fragment of human GHRH. Half-life ~6–8 minutes. Used for GH deficiency diagnosis. Related: GHRH, CJC-1295. See: CJC-1295 vs Sermorelin
SGLT2 Inhibitor Clinical. Sodium-glucose co-transporter 2 inhibitor. Blocks renal glucose reabsorption in proximal tubule. Examples: empagliflozin, dapagliflozin. Used for diabetes and heart failure. Related: insulin, diabetes, GLP-1. See: Peptide Interactions
Signaling Pathway Biology. Sequential molecular events that convert an extracellular signal into a cellular response. Includes: MAPK/ERK, PI3K/Akt, Wnt, Notch, TGF-β, JAK-STAT. Related: receptor, second messenger, kinase. See: Signaling
Solid-Phase Peptide Synthesis (SPPS) Chemistry. Method for stepwise peptide assembly on an insoluble resin support. Uses Fmoc or Boc protecting groups. Merrifield (Boc) and Fmoc/tBu are the two main strategies. Related: Fmoc, Boc, resin, coupling. See: SPPS
Somatostatin Biology. 14-amino acid hypothalamic peptide (SST-14) or 28-amino acid form (SST-28). Inhibits GH release from pituitary. Octreotide (somatostatin analog) is used for acromegaly, carcinoid tumors. Related: GH, GHRH, octreotide. See: Receptors
Structure-Activity Relationship (SAR) Chemistry. Relationship between chemical structure and biological activity. Used in drug design to optimize potency, selectivity, and pharmacokinetics. Related: medicinal chemistry, drug design. See: Computational
TB-500 (Thymosin Beta-4 Fragment) Pharmacology. Synthetic fragment of thymosin β4 (43 aa, residues 17–23 active domain). Promotes wound healing, angiogenesis, cell migration. Used in equine and veterinary medicine. Related: BPC-157, thymosin β4, wound healing. See: BPC-157 vs Thymosin Beta-4
Tmax Pharmacology. Time to reach maximum plasma concentration (Cmax) after drug administration. Indicates rate of absorption. Related: Cmax, bioavailability, absorption. See: Pharmacology
Testosterone Biology. Primary male androgenic steroid hormone (C₁₉H₂₈O₂, MW 288.42). Produced by Leydig cells. Activates androgen receptor for muscle growth, virilization, spermatogenesis. Converted to DHT (5α-reductase) and estradiol (aromatase). Related: androgen receptor, DHT, estradiol, SARM. See: Testosterone vs GHRP-6
Thymosin Beta-4 Biology. 43-amino acid peptide sequestering G-actin, preventing polymerization into F-actin. Regulates cell migration, wound healing, angiogenesis. TB-500 is a synthetic fragment. Related: TB-500, actin, wound healing. See: BPC-157 vs Thymosin Beta-4
Tirzepatide Clinical. Dual GIP/GLP-1 receptor agonist. Once-weekly SC injection (Mounjaro). 39 amino acids. Most effective weight loss agent approved. Related: semaglutide, GLP-1, GIP. See: Semaglutide vs Tirzepatide
Tissue Plasminogen Activator (tPA) Biology. Serine protease that converts plasminogen to plasmin (fibrinolysis). Alteplase, tenecteplase are recombinant forms used for stroke/MI thrombolysis. Related: plasmin, fibrinolysis, stroke. See: Therapeutic Peptides
Transdermal Delivery Pharmacology. Drug delivery through intact skin. Bypasses first-pass metabolism. Examples: testosterone patches, nicotine patches, fentanyl patches. Related: bioavailability, first-pass, skin permeability. See: Drug Delivery
Tuftsin Biology. Naturally occurring tetrapeptide (Thr-Lys-Pro-Arg) from IgG Fc region. Immunostimulant. Selank is a synthetic tuftsin analog. Related: selank, immunostimulant. See: Selank vs Semax
Vasopressin (ADH) Biology. 9-amino acid neuropeptide. Antidiuretic hormone that regulates water balance via V2 receptors in kidney. V1a receptors mediate vasoconstriction. Related: oxytocin, aquaporin. See: Oxytocin vs Vasopressin
Volume of Distribution (Vd) Pharmacology. Theoretical volume into which a drug distributes to achieve observed plasma concentration. Vd = dose / C₀. High Vd indicates extensive tissue distribution. Related: clearance, half-life, plasma protein binding. See: Pharmacology
Wnt Signaling Biology. Highly conserved signal transduction pathway regulating cell proliferation, differentiation, and polarity. Canonical (β-catenin) and non-canonical pathways. Related: β-catenin, bone metabolism, cancer. See: Signaling
Zwitterion Chemistry. Molecule with both positive and negative charges, net neutral. Amino acids at physiological pH exist as zwitterions (NH₃⁺ and COO⁻). Related: amino acid, isoelectric point, charge. See: Amino Acids