Reference
Peptide glossary
105 terms you will meet on a certificate of analysis, a product specification or a methods section — defined without hand-waving.
A
Acetate SaltWhere TFA would get in the way, acetate is the counter-ion of choice. Learn why licensed peptide medicines are acetates and what salt exchange really costs.AcetylationN-terminal acetylation blocks a peptide’s free amine, adds 42.01 Da and shields it from aminopeptidases. How it shows up on a COA and which vials carry it.Activin ReceptorActivin receptors (ActRIIA, ActRIIB, ALK4/7) are serine/threonine kinases that relay activin and myostatin signals through SMAD2/3. Definition and context.AliquotAn aliquot is a measured share taken from a stock solution. Learn why dividing a reconstituted peptide into single-use portions keeps the entire lot safe.Amide (C-Terminal Amidation)C-terminal amidation turns a peptide’s free acid into –CONH2, removing one charge and about 0.98 Da. Why that alters half-life and the expected MS mass.Amino AcidEvery peptide is assembled from amino acids. See how side chains govern solubility, oxidation risk and half-life, and why GLP-1 analogs contain Aib.AMPKAMPK is a three-part kinase switched on as the AMP:ATP ratio climbs. An overview of its subunits, the kinases above it and the metabolic targets below it.AmylinAmylin is a 37-residue hormone that beta-cells release together with insulin. Its receptors, its tendency to aggregate, and why analogs join GLP-1 studies.AnalogAn analog is a purposely modified version of a parent peptide. Four ways peptides get modified, and why analog findings never carry over to native molecules.Androgen ReceptorThe androgen receptor is a nuclear transcription factor switched on by testosterone and DHT. Its domains, how it signals, and why SARM research targets it.Antibody (Polyclonal vs Monoclonal)Polyclonals bind many epitopes and differ from lot to lot; monoclonals bind a single one and can be reproduced. Picking a format for peptide detection.AntiserumAntiserum is the complete serum of an immunised animal — target antibodies plus every other serum IgG and protein. What that implies for titre and background.
B
Bacteriostatic WaterBacteriostatic water is sterile water preserved with 0.9% benzyl alcohol so research vials can be entered repeatedly. When it suits peptide work.BDNFBDNF acts via TrkB and p75NTR, and proBDNF and mature BDNF pull in opposite directions. Definition, the Val66Met variant and why assays measure it so often.BioavailabilityBioavailability is the share of a given amount that enters the circulation unchanged. Why oral peptide values hover near 1% and injected ones reach about 80%.Bioregulator (Khavinson Peptide)Khavinson bioregulators are ultra-short di- to tetrapeptides first derived from tissue extracts. Their origin, the DNA-binding idea and the evidence base.Biotin LabelBiotin tags give a peptide a streptavidin handle of femtomolar strength. Where they are used in assays, and the linker, tissue biotin and recovery caveats.Blocking PeptideA blocking peptide is the free immunogen sequence used to pre-absorb an antibody and prove a band or stain is epitope-specific. How to set up the control.
C
Certificate of Analysis (COA)A COA is the batch-specific test report for a peptide: HPLC purity, MS identity, appearance and test date. The items a complete certificate has to include.Cold ChainA cold chain means continuous temperature control from production to storage. What it does, and does not, imply for lyophilised peptides shipped in summer.Compounding PharmacyCompounding pharmacies make patient-specific medicines under US FDCA sections 503A and 503B. How the two categories differ and why the peptide rules changed.Cosmetic Peptide (Signal Peptide)Skin-care peptides are sorted into signal, carrier, enzyme-inhibiting and neurotransmitter-modulating types. Reading INCI labels and weighing the data.Cyclic PeptideA cyclic peptide is closed into a ring through a covalent bond. The four ring types, and why cyclisation boosts protease resistance and selectivity.
D
DAC (Drug Affinity Complex)The Drug Affinity Complex links a peptide covalently to circulating albumin so its half-life moves from minutes to days. Consequences for experimental design.DegradationDegradation is any process that stops a peptide being the intended molecule: hydrolysis, deamidation, oxidation or aggregation. How each route shows up.Delta Sleep-Inducing Peptide (DSIP)DSIP is the nonapeptide WAGGDASGE, isolated in 1977 from rabbit cerebral venous blood. Its sequence, the missing-receptor problem and its research context.Disulfide BridgeA disulfide bridge is a covalent S–S bond linking two cysteines that fixes a peptide’s shape. Why scrambling is a risk and how a COA ought to report the bond.Dual AgonistA dual agonist is a single peptide designed to activate two receptors at a set potency ratio. Examples, the design rationale and why that ratio is decisive.
E
ELISAThe four ELISA formats — direct, indirect, sandwich and competitive — plus why short peptides call for competitive assays and how to read the standard curve.EndotoxinEndotoxin is bacterial lipopolysaccharide that acts at picogram levels and never shows on HPLC. Why a low-endotoxin grade is its own separate specification.ExcipientAn excipient is anything in a vial besides the active peptide, such as bulking agents, buffers or preservatives. Why they alter what you see and measure.
F
FDA-Approved vs Research-GradeFDA approval covers one product, one manufacturer and one indication under cGMP. Research-grade material shares the molecule but none of that framework.Fluorescent Label (FAM / FITC)Both are fluorescein dyes, but FAM and FITC attach differently and differ in stability. Ex/Em ~495/520 nm, pH dependence and handling of labelled peptides.FollistatinFollistatin is a secreted glycoprotein that disables activin and myostatin by enclosing the ligand dimer. The FST-288/315/344 isoforms and research context.Fragment (e.g. 176-191)A fragment is a defined section of a larger parent protein, named after its residue numbers. Why HGH Fragment 176-191 is not a miniature growth hormone.Freeze–Thaw CycleOne freeze–thaw cycle is a full trip from frozen to liquid and back again. Why every cycle erodes peptide integrity, and how aliquoting solves the problem.
G
GaugeNeedle gauge is an inverse scale: the bigger the number, the finer the needle. What 27G, 29G and 31G mean for peptide handling and why gauge influences shear.Ghrelin Receptor (GHS-R1a)GHS-R1a is the ghrelin receptor that GHRPs and MK-677 act on. Its high constitutive activity, the acylation requirement and how it desensitises over time.GHRHGHRH is a 44-residue hypothalamic peptide that acts on GHRHR in pituitary somatotrophs. Why its analogs end at residue 29 and how those analogs differ.GHRPGHRPs are synthetic agonists of the ghrelin receptor that cause pituitary GH release. How GHRP-2, GHRP-6, ipamorelin and hexarelin compare with each other.GIPGIP is the second incretin hormone, secreted by duodenal K-cells. Its receptor biology, its signalling in fat tissue and its place in dual-agonist research.GLP-1GLP-1 is an incretin hormone from the gut whose native half-life is only ~2 minutes. How it works, why DPP-4 cuts it, and why analogs lead metabolic research.GLP-1 Receptor AgonistA GLP-1 receptor agonist switches on the GLP-1 receptor and is built to resist proteases. The two structural families and how they differ in practice.Glucagon ReceptorThe glucagon receptor controls liver glucose output and energy expenditure. Why triple agonists such as retatrutide include a GCGR component in their design.Gray-Market VendorA gray-market vendor sits outside legitimate research-supply channels. Warning signs include human-use framing, recycled COAs and missing lot traceability.Growth Hormone SecretagogueA secretagogue prompts the pituitary to secrete its endogenous GH instead of adding hormone from outside. Three receptor classes and their feedback limits.
H
Half-LifeHalf-life is how long a concentration takes to fall by half. Peptide values range from two minutes to a week — and shelf stability is a different matter.HPLCHPLC separates a peptide from its impurities and gives purity as area percent at a fixed wavelength. What that figure includes, and what it overlooks.Hyaluronic AcidHyaluronic acid is an unbranched, non-sulfated polysaccharide of repeating sugar pairs. How chain size, CD44 signalling and handling shape research results.HydrophilicHydrophilic means attracted to water. Why most research peptides dissolve easily in bacteriostatic water, yet the same trait stops them crossing membranes.
I
I-125 RadiolabelIodine-125 tags peptides at tyrosine residues for RIA and receptor-binding work. Its half-life, specific activity and the licensing it requires in the lab.IGF Binding ProteinIGFBPs hold more than 95% of circulating IGF-1, governing its half-life and tissue access. The six family members and why analogs are built to evade them.IGF-1IGF-1 is a 70-residue peptide, made mostly in the liver, that carries growth hormone signalling. Its receptor, its binding proteins and why LR3 and DES exist.ImmunogenAn immunogen is the material used to immunise a host and raise an antibody. Why short peptides need a KLH or BSA carrier; the sequence predicts specificity.In VitroIn vitro means outside a living organism — cell culture, receptor binding or enzyme assays. What these data can and cannot support in peptide research.In VivoIn vivo means inside a living organism. What animal studies add beyond cell work, how to judge model and species claims, and where translation tends to fail.IncretinIncretins are intestinal hormones that amplify insulin output once food arrives. The incretin effect, the roles of GIP and GLP-1, and the DPP-4 problem.Insulin Syringe Units (U-100)U-100 syringe marks measure volume: 100 units fill 1 mL, so one unit is 0.01 mL. The peptide amount per unit depends only on your own reconstitution.IntranasalNasal delivery puts a peptide solution on the nasal lining, avoiding hepatic first-pass loss. Surface area, clearance time and the nose-to-brain question.Isoelectric Point (pI)At its isoelectric point a peptide carries no net charge and is least soluble. Using the pI to fix a cloudy vial after reconstitution and plan purification.
L
Linear PeptideLinear peptides are straight, unbranched residue chains with open termini and no cyclisation. Why they dominate research catalogues and what that costs.LipophilicLipophilic means fat-loving: the molecule prefers a lipid phase over water. Why lipophilic residues promote aggregation and how they enable albumin binding.Lot NumberA lot number links a particular vial to a particular batch and its test results. Why every claim on a peptide COA is lot-bound and how to check the match.Luer-LockLuer-lock fittings twist a needle onto the syringe tip with a thread instead of a press fit. Why that secure joint matters for filters and thick solutions.LyophilizedA lyophilized peptide has been freeze-dried under vacuum. How to read the dried cake in a vial, why powder ships better than solution, and warning signs.
M
MannitolMannitol is a sugar alcohol added as a bulking agent to freeze-dried peptide vials. Why it forms a visible cake and what it means for your mass calculations.Mass SpectrometryMS verifies which peptide is in a vial by comparing its measured mass with the mass calculated from the sequence. How to read the MS line on a certificate.MatrikineMatrikines are peptide fragments cut from extracellular matrix proteins that then act as signalling molecules themselves. Definition and key examples.Micrograms vs Milligrams1 mg is 1,000 mcg. Why peptide vials state milligrams, why papers report micrograms, and how to avoid slipping a factor of 1000 during conversion.MolarityMolarity counts moles of dissolved substance per litre. Why in-vitro peptide work is reported in nM or µM, and how to get there from a mg/mL concentration.Molecular Weight (Da)A peptide’s molecular weight in daltons links mass to moles and underpins MS identity checks. Also covers average versus monoisotopic mass on a certificate.Myostatin (GDF-8)Myostatin, a growth factor of the TGF-beta family, restrains skeletal muscle mass via ActRIIB and SMAD2/3. Its processing, latency and research background.
N
NAD+NAD+ is a redox cofactor that sirtuins, PARPs and CD38 also consume as a substrate. What that dual role means for metabolic models and lab handling.Native SequenceA native sequence matches a peptide exactly as it occurs in a stated species, with no substitutions. Why the species matters and why native is rarely durable.NeurotrophinThe neurotrophins (NGF, BDNF, NT-3, NT-4/5) are four growth factors that signal via Trk receptors and p75NTR. Their structure, receptors and research context.NMNNicotinamide mononucleotide sits one step before NAD+: NAMPT makes it, NMNAT converts it. Chemistry, the cellular uptake debate and how it is studied.NootropicGiurgea coined the word nootropic in 1972 and set five criteria that most marketed compounds fail. What the term actually means in peptide research today.
P
PDRNPDRN is a mix of salmon-gonad DNA fragments (50-1,500 kDa), studied for A2A adenosine receptor signalling and nucleotide salvage. What it is and is not.PEGylationPEGylation links polyethylene glycol to a peptide so the kidneys clear it more slowly. What it changes for half-life, for mass and for reading the vial label.PeptidePeptides are short chains of amino acids joined by peptide bonds. Where chemists separate them from proteins, and what the name on a vial never reveals.Peptide BondA peptide bond is the amide link that joins one amino acid to the next. Its planarity, how slowly it hydrolyses and its part in SPPS impurities.PPAR-deltaPPAR-delta (PPARD, NR1C2) is a fatty-acid-sensing nuclear receptor that partners with RXR. Its role in muscle metabolism and the GW-501516 research context.PreclinicalPreclinical covers all research before a compound reaches humans: in vitro work, animal pharmacology, ADME and GLP toxicology to support an IND. Definition.Purified IgGPurified IgG is the immunoglobulin fraction separated from serum. Protein A/G purification and peptide-affinity purification are two very different things.PurityPeptide purity is an HPLC area percentage, not a measure of peptide content. What ≥98% includes, what it hides, and why net peptide is reported apart.
R
RecombinantRecombinant means made by an engineered host cell instead of by chemical synthesis. Where the switch-over from synthesis lies and how the impurities differ.ReconstitutionReconstitution means dissolving a freeze-dried peptide in a solvent to reach a known concentration. The mg/mL calculation, solvent choice and handling basics.REV-ERBREV-ERB alpha and beta are nuclear receptors that bind heme, switch off BMAL1 and connect circadian timing with metabolic genes. Meaning and research context.RIA (Radioimmunoassay)Radioimmunoassay is a competitive test using an I-125 tracer, invented by Yalow and Berson. The principle, and why it keeps a niche for very small peptides.
S
SARM (Selective Androgen Receptor Modulator)SARMs are non-steroid androgen receptor ligands designed to act selectively by tissue. Their chemistry, the selectivity idea and their US regulatory position.SirtuinThe seven sirtuins, SIRT1 to SIRT7, strip acyl groups from proteins using NAD+, each in its own compartment. Roles, and why NAD+ levels set their activity.Solid-Phase Peptide Synthesis (SPPS)SPPS assembles a peptide on resin from the C-terminus, with one deprotect-and-couple cycle per residue. Why coupling efficiency caps the purity you can reach.SomatostatinSomatostatin acts as the brake on the growth hormone axis via five SSTR subtypes. Its two forms, its 3-minute half-life and why it matters in research design.Species ReactivitySpecies reactivity lists which species’ target an antibody or kit detects. Tested versus predicted reactivity, sequence homology and the host-species trap.StabilityStability describes how well a peptide keeps its structure over time under set conditions. The five factors that determine it, ranked by practical impact.Sterile WaterSterile water has no preservative, so a vial reconstituted with it is single-entry. When a preservative-free solvent is the correct choice for peptide work.SubcutaneousSubcutaneous refers to the fatty tissue layer under the skin. Why it is the standard parenteral route in peptide animal studies, and the limits on its volume.Sublingual TrocheA troche is a soft lozenge that dissolves beneath the tongue. How the sublingual route works, why peptide uptake there is limited, and what you should check.Synthetic (SPPS)Synthetic peptides are built chemically on resin beads, one amino acid per cycle. How this shapes purity, allows non-natural residues and defines a good COA.
T
TetrapeptideA tetrapeptide consists of four amino acids linked by three peptide bonds. Why this length turns up in bioregulators, matrikines and cosmetic peptides.TFA SaltMost synthetic peptides are supplied as trifluoroacetate salts. How much of the vial mass is counter-ion, and when TFA can interfere with cell-based assays.Third-Party TestingIndependent testing means a lab with no stake in the sale analyses a sample of the lot. What these reports prove, their blind spots, and how to check one.TripeptideTripeptides are three amino acids joined through two peptide bonds. Profiles of GHK, KPV, glutathione and TRH, and how such a short chain affects handling.Triple AgonistTriple agonists activate the GLP-1, GIP and glucagon receptors with one molecule. The rationale for the glucagon arm and what published studies examined.
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