Reference
Peptide Research Glossary
A-Z definitions for the terminology that shows up in research peptide product pages, Certificates of Analysis, and the rest of the /learn library. Bookmark and reference as needed.
- Acetate (salt form)
- A salt form a peptide can ship as. Acetate salts contribute mass to the powder, so a 10 mg vial of an acetate salt has slightly less of the active peptide than 10 mg of the free base. The COA should specify the salt form.
- Agonist
- A molecule that binds a receptor and activates it, producing the same downstream signal as the natural ligand. Most research peptides in the metabolic and growth-hormone classes are agonists.
- Alpha-MSH
- Alpha-melanocyte-stimulating hormone, the natural ligand for the melanocortin-1 receptor on skin melanocytes. Several research peptides (PT-141, Melanotan 2, KPV) are derivatives or fragments of alpha-MSH.
- Amino acid
- The building block of peptides and proteins. There are 20 standard amino acids that the genetic code encodes, plus a small number of non-standard amino acids used in synthetic peptides for stability or potency.
- AMPK
- AMP-activated protein kinase. A cellular energy sensor that activates when ATP is low, triggering fatty-acid oxidation and inhibiting anabolic pathways. MOTS-c and several metabolic peptides act through AMPK.
- Antagonist
- A molecule that binds a receptor without activating it, blocking the natural ligand from binding. Less common in the research peptide space than agonists.
- Bacteriostatic water
- Sterile water with 0.9 percent benzyl alcohol added as a preservative. The standard solvent for reconstituting research peptides because it keeps the solution stable for two to four weeks at refrigeration temperature. Read more →
- BDNF
- Brain-derived neurotrophic factor. A growth factor that supports neuron survival and synaptic plasticity. Semax dosing upregulates BDNF expression in animal models. Read more →
- Bioavailability
- The fraction of a dose that reaches the bloodstream in active form. Most research peptides have low oral bioavailability because stomach acid and digestive enzymes degrade them, which is why injection is the standard route.
- BPC-157
- A 15-amino-acid peptide derived from a fragment of body protection compound. Studied in tendon and ligament injury models, gastrointestinal repair, and traumatic brain injury models. Read more →
- Cofactor
- A non-protein molecule that an enzyme needs to function. NAD+ is the most-studied cofactor in cellular energy metabolism. Read more →
- COA (Certificate of Analysis)
- The lab report that backs up a product label. A complete COA reports identity (mass spec), purity (HPLC), appearance, and contaminants (residual solvent, endotoxin, microbial). Read more →
- Cytokine
- A small signaling protein released by immune cells to coordinate immune response. Many recovery peptides have documented effects on cytokine balance.
- DPP-4
- Dipeptidyl peptidase-4, an enzyme that rapidly degrades many incretin peptides including native GLP-1. Most modern GLP-1 receptor agonists are structurally modified to resist DPP-4 cleavage, extending their half-life from minutes to days.
- Endotoxin
- A component of the outer membrane of gram-negative bacteria that triggers a strong immune response in mammals. Research peptides for injection must have endotoxin levels well below safety thresholds, measured by the LAL test.
- GHRH
- Growth-hormone-releasing hormone. A 44-amino-acid hypothalamic peptide that signals the pituitary to release growth hormone. Sermorelin and tesamorelin are synthetic GHRH analogs. Read more →
- GHS-R
- Growth-hormone secretagogue receptor. A pituitary receptor activated by ghrelin and by synthetic secretagogues like ipamorelin. Activation amplifies the natural GH pulse. Read more →
- GIP
- Glucose-dependent insulinotropic polypeptide. The second major incretin hormone after GLP-1. Dual GLP-1 + GIP agonists are the current generation of metabolic research peptides. Read more →
- GLP-1
- Glucagon-like peptide-1. An incretin hormone released by the gut after meals. Amplifies insulin release, slows gastric emptying, and signals satiety. The most-studied receptor target in current metabolic peptide research. Read more →
- Glucagon
- A hormone that raises blood glucose by signaling the liver to release stored glucose, and increases energy expenditure. Glucagon receptor agonism is the third receptor in triple-agonist metabolic peptides like retatrutide. Read more →
- Half-life
- The time it takes for the concentration of a molecule in the body to drop by half. Native peptide half-lives are usually minutes; synthetic analogs with structural modifications can extend half-life to days or weeks.
- HPLC
- High-performance liquid chromatography. The standard analytical method for measuring peptide purity. Separates a sample into component peaks and reports each as a percentage of the total. Read more →
- IGF-1
- Insulin-like growth factor 1. The downstream signaling molecule of growth hormone, produced primarily by the liver. Mediates most of the anabolic effects attributed to growth hormone. Read more →
- Incretin
- A class of gut hormones (primarily GLP-1 and GIP) that amplify insulin release in response to food. Targeted by most metabolic research peptides.
- KPV
- A tripeptide consisting of lysine, proline, and valine. The C-terminal fragment of alpha-MSH. Studied for anti-inflammatory effects, especially in mucosal tissue. Read more →
- LAL test
- Limulus amebocyte lysate test. The standard assay for endotoxin detection in injectable preparations. Reported in endotoxin units (EU) per milligram of peptide.
- Lyophilized
- Freeze-dried. The standard form research peptides ship in. Removing water makes the peptide stable at room temperature for days and at refrigeration temperature for one to two years for most sequences.
- MC1R / MC3R / MC4R / MC5R
- Melanocortin receptor subtypes. MC1R is on melanocytes and controls pigmentation. MC3R and MC4R are central and involved in appetite and sexual response. MC5R is less well-characterized. Read more →
- Mass spectrometry (MS)
- An analytical technique that measures the mass of a molecule. Used to confirm peptide identity by comparing observed mass to the calculated mass of the target sequence. Should appear on a complete COA. Read more →
- Melanocyte
- A cell type in the skin and hair follicles that produces melanin. Activated through the MC1R receptor by alpha-MSH and synthetic analogs like Melanotan 2. Read more →
- Mitochondria
- The organelles inside cells that generate ATP through oxidative phosphorylation. Have their own small circular genome encoding 13 proteins plus a small number of regulatory peptides like MOTS-c. Read more →
- MOTS-c
- A 16-amino-acid peptide encoded inside the mitochondrial genome. Acts as a signaling molecule, activating AMPK and affecting insulin sensitivity and metabolic flexibility. Read more →
- NAD+
- Nicotinamide adenine dinucleotide. A cellular cofactor essential for the electron transport chain and for sirtuin enzyme activity. Levels decline with age, making NAD+ a major focus of longevity research. Read more →
- Peptide
- A short chain of amino acids, usually defined as fewer than 50. Above 50 amino acids the molecule is typically called a protein, though the line is fuzzy.
- Pituitary
- A small endocrine gland at the base of the brain that releases growth hormone, ACTH, and several other hormones in response to hypothalamic signals. The target of GHRH analogs and growth-hormone secretagogues.
- Pulsatile release
- A pattern of hormone release in discrete bursts rather than continuous flow. Growth hormone is naturally released in pulses, mostly during deep sleep, and the pulsatile rhythm matters for downstream signaling.
- Reconstitution
- The process of adding bacteriostatic water (or sterile water) to a lyophilized peptide vial to turn the powder into a solution. Read more →
- Receptor
- A protein on or inside a cell that binds a specific molecule and triggers a downstream signal. Most research peptides act by binding receptors and either activating them (agonist) or blocking them (antagonist).
- Secretagogue
- A molecule that stimulates the release of a hormone from a gland. Growth-hormone secretagogues like ipamorelin act on the ghrelin receptor (GHS-R) on the pituitary to amplify GH release. Read more →
- Sirtuin
- A family of NAD+-dependent enzymes that regulate gene expression and DNA repair. Sirtuin activity depends on NAD+ supply, which is part of why NAD+ has become central to longevity research.
- Subcutaneous
- Beneath the skin. The standard route of administration for most research peptides. Faster absorption than intramuscular for small molecules, easier to self-administer.
- TB-500
- A synthetic version of an active fragment of thymosin beta-4. Studied for cell migration in wound healing and tendon repair. Often combined with BPC-157 in recovery research. Read more →
- Tesamorelin (TH9507)
- A modified GHRH analog that resists enzymatic degradation. FDA-approved for visceral fat reduction in HIV-associated lipodystrophy. Studied beyond the approved indication for broader metabolic endpoints. Read more →
- Thymosin alpha-1
- A 28-amino-acid peptide originally isolated from the thymus. One of the most-studied peptides in immune modulation research, with applications in viral hepatitis, sepsis, and oncology adjunct settings. Read more →
- TLR (Toll-like receptor)
- A family of pattern-recognition receptors on immune cells that detect pathogen-associated molecular patterns. Thymosin alpha-1 acts in part through TLR2 and TLR9 signaling.
- Trifluoroacetate (TFA)
- A salt form some peptides ship as. Like acetate, it contributes mass to the powder. Most modern research peptide suppliers ship as acetate or free base to avoid the higher mass contribution of TFA.
- Triple agonist
- A peptide that activates three receptors at once. Retatrutide is the most-studied triple agonist, activating GLP-1, GIP, and glucagon receptors in a specific ratio. Read more →
- Tyrosinase
- The enzyme that converts tyrosine into the precursors of melanin pigment. Upregulated in melanocytes after MC1R activation by alpha-MSH or synthetic analogs.
- U-100 insulin syringe
- A syringe graduated in 100 units per milliliter. The standard syringe for self-administered peptide research. Each unit is 0.01 mL of solution. Read more →
- VEGF / VEGFR2
- Vascular endothelial growth factor and its receptor type 2. Drive new blood-vessel formation. BPC-157 dosing in animal models upregulates VEGFR2 expression at injury sites, which fits the observed vascular effects of the peptide.
Missing a term?
Email hello@lidobs.com and we will add it. This glossary is intended as a living reference for anyone reading the research peptide literature.