Reference
Peptide glossary
106 terms you will meet on a certificate of analysis, a product specification or a methods section — defined without hand-waving.
A
Acetate SaltAcetate is the preferred counter-ion where TFA would interfere. Why approved peptide drugs ship as acetates and what salt exchange costs.AcetylationN-terminal acetylation caps a peptide's free amine, adds 42.01 Da and blocks aminopeptidases. What it changes on a COA and which products carry it.Activin ReceptorActivin receptors are serine/threonine kinase receptors (ActRIIA, ActRIIB, ALK4/7) that transduce activin and myostatin signals via SMAD2/3. Definition.AliquotAn aliquot is a measured portion split off from a stock solution. Why splitting a reconstituted peptide into single-use portions protects the whole lot.Amide (C-Terminal Amidation)C-terminal amidation replaces the peptide's free acid with –CONH2, cutting one charge and 0.98 Da. Why it changes half-life and expected MS mass.Amino AcidAmino acids are the monomers of every peptide. How side chains set solubility, oxidation risk and half-life, and why Aib appears in GLP-1 analogs.AMPKAMPK is a heterotrimeric kinase activated when the AMP:ATP ratio rises. Its subunits, upstream kinases and its downstream metabolic targets.AmylinAmylin is a 37-residue beta-cell hormone co-secreted with insulin. Its receptors, aggregation problem, and why analogs pair with GLP-1 research.AnalogAn analog is a deliberately modified version of a parent peptide. The four modification types, and why analog data never transfers to the native molecule.Androgen ReceptorThe androgen receptor is a ligand-activated nuclear transcription factor bound by testosterone and DHT. Domains, mechanism and why SARMs target it.Antibody (Polyclonal vs Monoclonal)Polyclonal antibodies recognise many epitopes and vary by lot; monoclonals recognise one and are renewable. How to choose for peptide detection work.AntiserumAntiserum is whole serum from an immunised animal: the target antibodies plus all other serum IgG and proteins. What that means for titre and background.
B
Bacteriostatic WaterBacteriostatic water is sterile water with 0.9% benzyl alcohol as a preservative, allowing multi-draw research vials. When it suits peptide work.BDNFBDNF signals through TrkB and p75NTR; proBDNF and mature BDNF have opposing effects. Definition, the Val66Met variant and why it is a common readout.BioavailabilityBioavailability is the fraction of an administered amount reaching circulation intact. Why oral peptide figures sit near 1% and injected near 80%.Bioregulator (Khavinson Peptide)Khavinson bioregulators are very short peptides, mostly di- to tetrapeptides, from tissue extracts. Origin, DNA-binding claim and evidence.Biotin LabelBiotinylation gives a peptide a femtomolar handle for streptavidin capture. Spacer length, endogenous biotin and elution limits explained.Blocking PeptideA blocking peptide is the free immunogen peptide used to pre-adsorb an antibody and confirm a band or stain is epitope-specific. How to run it.
C
Certificate of Analysis (COA)A COA is the lot-specific test record for a peptide: HPLC purity, MS identity, appearance and date. What a complete certificate must contain.Cold ChainThe cold chain is unbroken temperature control from manufacture to storage. What it does and does not mean for lyophilised peptides shipped in summer.Compounding PharmacyCompounding pharmacies prepare patient-specific medications under FDCA sections 503A and 503B. How the categories differ and why peptide rules changed.Cosmetic Peptide (Signal Peptide)Cosmetic peptides split into signal, neurotransmitter-inhibiting, carrier and enzyme-inhibitor classes. What INCI names mean and how to read the evidence.Cyclic PeptideA cyclic peptide is closed into a ring by a covalent bond. Why cyclisation raises protease resistance and receptor selectivity, and the four ring types.
D
DAC (Drug Affinity Complex)DAC is a maleimide linker that binds a peptide to serum albumin, extending circulating half-life from minutes to days. What it changes in research design.DegradationDegradation covers every route by which a peptide stops being itself: hydrolysis, deamidation, oxidation, aggregation. What each looks like.Delta Sleep-Inducing Peptide (DSIP)DSIP is a nonapeptide (WAGGDASGE) isolated from rabbit cerebral venous blood in 1977. Sequence, the unidentified receptor problem and research context.Disulfide BridgeA disulfide bridge is a covalent S–S bond between two cysteines that locks peptide shape. Why scrambling matters and how a COA should report it.Dual AgonistA dual agonist is one peptide engineered to activate two receptors at a defined potency ratio. Examples, design logic and why ratios matter.
E
ELISAELISA formats (direct, indirect, sandwich, competitive) explained, plus why short peptides need competitive assays and how to read the standard curve.EndotoxinEndotoxin is bacterial lipopolysaccharide, active at picogram levels and invisible to HPLC. Why low-endotoxin grade is a separate specification.ExcipientAn excipient is any component of a vial other than the active peptide — bulking agents, buffers, preservatives. Why they change what you see and measure.
F
FDA-Approved vs Research-GradeFDA approval covers a specific product, manufacturer and indication under cGMP. Research-grade material shares a molecule, not that framework.Fluorescent Label (FAM / FITC)FAM and FITC are fluorescein-based peptide labels with different linkage chemistry and stability. Ex/Em ~495/520 nm, pH sensitivity and handling explained.FollistatinFollistatin is a secreted glycoprotein that neutralises activin and myostatin by wrapping the ligand dimer. Isoforms FST-288/315/344 and research context.Fragment (e.g. 176-191)A fragment is a defined stretch of a larger parent protein, named by residue numbers. Why HGH Fragment 176-191 is not growth hormone in miniature.Freeze–Thaw CycleA freeze–thaw cycle is one round trip from frozen to liquid and back. Why each one costs peptide integrity, and how aliquoting removes the problem.
G
GaugeNeedle gauge runs backwards: a higher number means a thinner needle. What 27G, 29G and 31G mean for peptide handling, and why gauge affects shear.Ghrelin Receptor (GHS-R1a)GHS-R1a is the ghrelin receptor targeted by GHRPs and MK-677. Its constitutive activity, acylation requirement and desensitisation behaviour.GHRHGHRH is a 44-residue hypothalamic peptide acting at GHRHR on pituitary somatotrophs. Why analogs stop at residue 29 and how they differ.GHRPGHRPs are synthetic ghrelin-receptor agonists that trigger pituitary GH release. How GHRP-2, GHRP-6, ipamorelin and hexarelin differ.GIPGIP is the second incretin, released from duodenal K-cells. Its receptor biology, adipose signalling, and its role in dual-agonist research.GLP-1GLP-1 is a gut incretin hormone with a ~2 minute native half-life. Its biology, DPP-4 cleavage, and why analogs dominate metabolic research.GLP-1 Receptor AgonistA GLP-1 receptor agonist activates the GLP-1 receptor with engineered protease resistance. The two structural families and how they differ.Glucagon ReceptorThe glucagon receptor drives hepatic glucose output and energy expenditure. Why triple agonists such as retatrutide add a GCGR arm.Gray-Market VendorA gray-market vendor sells research-labelled material while signalling human use. The red flags: human framing, recycled COAs, no traceability.Growth Hormone SecretagogueA GH secretagogue prompts the pituitary to release its own growth hormone. The three mechanistic groups and how they differ from exogenous HGH.
H
Half-LifeHalf-life is the time for a concentration to fall by half. Peptide values run from two minutes to a week, and shelf stability is a separate thing.HPLCHPLC separates a peptide from its impurities and reports purity as area percent at a set wavelength. What the number covers and what it misses.Hyaluronic AcidHyaluronic acid is a non-sulfated glycosaminoglycan of repeating disaccharides. Molecular weight, CD44 signalling and lab handling explained.HydrophilicHydrophilic means water-loving. Why most research peptides dissolve readily in bacteriostatic water and why the same property blocks membrane crossing.
I
I-125 RadiolabelIodine-125 labels peptides at tyrosine residues for RIA and receptor binding. Half-life, specific activity and licence requirements explained.IGF Binding ProteinIGFBPs bind over 95% of circulating IGF-1, controlling its half-life and tissue availability. The six family members and why analogs evade them.IGF-1IGF-1 is a 70-residue hepatic mediator of growth hormone action. Its receptor, binding proteins, and why LR3 and DES analogs exist.ImmunogenAn immunogen is the substance used to raise an antibody. Why short peptides need KLH or BSA carriers, and why the immunogen sequence predicts specificity.In VitroIn vitro means outside a living organism: cell culture, receptor binding, enzyme assays. What such data can and cannot support for peptide research.In VivoIn vivo means within a living organism. What animal studies add over cell work, how to read model and species claims, and where translation usually fails.IncretinIncretins are gut hormones that amplify insulin release after oral nutrients. The incretin effect, GLP-1 and GIP, and why DPP-4 limits them.Insulin Syringe Units (U-100)On a U-100 syringe, 100 units equal 1 mL, so one unit is 0.01 mL. Units are volume marks, not peptide content — here is how researchers convert correctly.IntranasalIntranasal delivery crosses the nasal mucosa, bypassing first-pass metabolism. Surface area, mucociliary clearance and the nose-to-brain debate.Isoelectric Point (pI)The pI is the pH at which a peptide carries no net charge — and where it is least soluble. How to use it when a vial refuses to go clear.
L
Linear PeptideA linear peptide is an unbranched chain with free N- and C-termini and no ring closure. Why most research peptides are linear and what that costs them.LipophilicLipophilic means fat-loving: a molecule partitions into lipid rather than water. Why lipophilic residues drive aggregation and albumin binding.Lot NumberA lot number ties a specific vial to a specific batch and its test data. Why every peptide COA claim is lot-bound and how to verify a match.Luer-LockA luer-lock is a threaded syringe fitting that screws the needle on rather than pushing it. Why it matters for filtration and viscous transfers in the lab.LyophilizedLyophilized means freeze-dried under vacuum. What the cake in a peptide vial tells you, why powder ships better than solution, and what to check.
M
MannitolMannitol is a sugar alcohol used as a bulking agent in lyophilised peptide vials. Why it builds a visible cake and what it means for your mass calculation.Mass SpectrometryMass spectrometry confirms peptide identity by matching observed mass to the theoretical mass of the sequence. How to read the MS line on a COA.MatrikineMatrikines are peptide fragments released by proteolysis of extracellular matrix proteins that act as signals in their own right. Definition and examples.Micrograms vs MilligramsOne milligram is 1,000 micrograms. Why vials are labelled in mg while research reports mcg, and where the factor-of-1000 error creeps in.MolarityMolarity is moles of solute per litre of solution. Why in-vitro peptide work is specified in nM or µM, and how to convert from a mg/mL vial concentration.Molecular Weight (Da)Molecular weight in daltons links milligrams to moles and lets mass spectrometry confirm identity. Monoisotopic vs average mass explained.Myostatin (GDF-8)Myostatin is a TGF-beta family growth factor that limits skeletal muscle mass through ActRIIB and SMAD2/3. Processing, latency and research context.
N
NAD+NAD+ (nicotinamide adenine dinucleotide) is a redox cofactor and a consumed substrate for sirtuins, PARPs and CD38. What that means in lab work.Native SequenceA native sequence matches the peptide as it occurs in a given species, with no substitutions. Why species matters and why native is not durable.NeurotrophinNeurotrophins are a four-member growth factor family (NGF, BDNF, NT-3, NT-4/5) signalling through Trk receptors and p75NTR. Structure and research context.NMNNMN is the immediate NAD+ precursor made by NAMPT and converted by NMNAT enzymes. Its chemistry, transport debate and research context, explained.NootropicNootropic, coined by Giurgea in 1972, has five original criteria most marketed compounds fail. What the term means in peptide research today.
P
PDRNPDRN is a mixture of DNA fragments (50-1,500 kDa) from salmon gonads, studied via adenosine A2A receptor and salvage-pathway mechanisms. Definition.PEGylationPEGylation attaches polyethylene glycol to a peptide to slow renal clearance. What it does to half-life, mass and label interpretation.PeptideWhat a peptide is: a chain of amino acids joined by peptide bonds, where the protein boundary sits, and what a peptide label does not tell you.Peptide BondThe peptide bond is the amide linkage joining amino acids. Its planarity, hydrolysis kinetics and role in SPPS impurities, explained for lab use.PPAR-deltaPPAR-delta (PPARD, NR1C2) is a fatty-acid-sensing nuclear receptor that heterodimerises with RXR. Its biology and why GW-501516 is studied against it.PreclinicalPreclinical describes research conducted before human administration: in vitro, animal pharmacology, ADME and GLP toxicology supporting an IND. Definition.Purified IgGPurified IgG means the immunoglobulin fraction isolated from serum. Protein A/G purification and peptide-affinity purification are not the same thing.PurityPeptide purity is an HPLC area percentage, not peptide content. What ≥98% covers, what it hides, and why net peptide is a separate number.
R
RecombinantRecombinant means produced by an engineered host cell rather than by chemistry. Where the crossover with synthesis sits and what impurities differ.ReconstitutionReconstitution is dissolving a lyophilized peptide in solvent to a known concentration. The mg/mL calculation, solvent choice and handling basics.Research Use Only (RUO)RUO labels material intended for laboratory investigation only — not for diagnostic or human use. What the designation means and what it does not.REV-ERBREV-ERB alpha and beta are heme-binding nuclear receptors that repress BMAL1 and link the circadian clock to metabolism. Definition and research context.RIA (Radioimmunoassay)RIA is a competitive immunoassay using an I-125 tracer, developed by Yalow and Berson. How it works and why it persists for small peptides.
S
SARM (Selective Androgen Receptor Modulator)A SARM is a non-steroidal androgen receptor ligand designed for tissue-selective activity. Chemistry, the selectivity hypothesis and US regulatory status.SirtuinSirtuins are NAD+-dependent deacylases (SIRT1-7) with distinct subcellular homes. What they do and why NAD+ supply gates their activity.Solid-Phase Peptide Synthesis (SPPS)SPPS builds a peptide chain on resin, C-terminus first, one deprotect-and-couple round per residue. Why coupling efficiency sets the ceiling on purity.SomatostatinSomatostatin is the brake on the growth hormone axis, acting at five SSTR subtypes. Its two forms, 3-minute half-life and research relevance.Species ReactivitySpecies reactivity states which species' target an antibody or kit recognises. Predicted vs tested reactivity, sequence homology and the host-species trap.StabilityStability is how well a peptide keeps its structure over time under defined conditions. The five factors that decide it, ranked by impact.Sterile WaterSterile water contains no preservative, so a reconstituted vial is single-entry. When preservative-free solvent is the right choice in peptide work.SubcutaneousSubcutaneous means into the fatty layer beneath the skin. Why it is the default parenteral route in peptide animal studies, and its volume limits.Sublingual TrocheA troche is a soft lozenge that dissolves under the tongue. How the sublingual route works, why peptide absorption there is limited, and what to check.Synthetic (SPPS)Synthetic peptides are built chemically, residue by residue, on a solid resin. What that means for purity, non-natural residues and what a COA should show.
T
TetrapeptideA tetrapeptide is four amino acids joined by three peptide bonds. Why this length recurs in bioregulators, matrikines and cosmetic peptides.TFA SaltMost synthetic peptides ship as trifluoroacetate salts. How much of the vial mass is counter-ion, and when TFA interferes with cell-based assays.Third-Party TestingThird-party testing means an independent lab with no commercial stake analyses the lot. What it verifies, what it cannot, how to check it.TripeptideA tripeptide is three amino acids joined by two peptide bonds. GHK, KPV, glutathione and TRH explained, plus why chain length drives handling.Triple AgonistA triple agonist activates GIP, GLP-1 and glucagon receptors from one backbone. Why the third arm was added and what research has examined.
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