Research Peptide Glossary: 120+ Terms Explained (A–Z)

This peptide glossary defines more than 120 terms that appear on certificates of analysis, product labels, supplier pages and published papers about research peptides — from acetylation and bacteriostatic water through lyophilisation, net peptide content and zwitterion. Each entry is written for laboratory researchers who need a precise, checkable definition rather than a marketing gloss. Entries are grouped A to Z with anchor links, and cross-reference the relevant GenoPept research guides. Research use only.

Updated 10 September 2026~22 min readReviewed by the GenoPept technical team

How to use this glossary

Every entry has its own anchor, so a term can be linked directly — for example the definition of lyophilised sits at the anchor #term-lyophilised. Definitions are deliberately short and specific, and where a term deserves a full treatment the entry links to the relevant GenoPept research guide rather than repeating it.

The glossary covers four families of vocabulary: peptide chemistry, analytical quality control, laboratory handling, and the regulatory and commercial language that surrounds research-use-only supply. Terms that belong to a specific compound class — incretin, secretagogue, bioregulator — are included where they are widely used across the literature.

Peptide anatomy: the terms on every diagram

Most of the structural vocabulary in this glossary refers to a small number of features on a single molecule. The figure below labels them once so the definitions later can stay short.

Units, concentrations and conversions

The second cluster of vocabulary concerns quantity. Research peptides are supplied by mass, prepared as concentrations, sometimes measured in moles and — for glycoprotein hormones — quantified in International Units instead. The figure and table below fix the relationships.

A

Acetylation

Addition of an acetyl group to a peptide’s N-terminal amino group. It removes the free amine that aminopeptidases require, so acetylated analogues are described in the literature as more resistant to enzymatic trimming than their unmodified parents. Written as “Ac-” before the sequence.

Acetate salt

A peptide supplied with acetate as its counter-ion rather than trifluoroacetate. Salt form affects the mass of the vial contents without changing the peptide, which is why net peptide content and salt form should both appear on a certificate of analysis.

Acylation

Attachment of a fatty acid chain, usually to a lysine side chain, sometimes through a linker. In GLP-1 research peptides acylation promotes reversible albumin binding, which is the main structural strategy for extending circulating lifetime. See the GLP-1 guide.

Agonist

A ligand that binds a receptor and activates it, producing the same class of response as the endogenous signal. A full agonist reaches the maximal response; a partial agonist plateaus below it even at saturating concentrations.

Aggregation

Association of peptide molecules into dimers, oligomers or insoluble particles. It is promoted by agitation, freeze–thaw stress, concentration and unfavourable pH, and it reduces the amount of monomeric peptide available without necessarily changing the total mass present.

Aliquot

A measured portion of a stock solution divided out for single use. Aliquoting before freezing is the standard way to avoid repeated freeze–thaw stress on the whole batch, and it makes every subsequent experiment traceable to one preparation event.

Amidation

Conversion of a peptide’s C-terminal carboxyl group to a carboxamide, written “-NH2” at the end of a sequence. It blocks carboxypeptidase attack and, in many natural peptides such as GnRH and kisspeptin, is required for full receptor potency rather than optional.

Amino acid

The monomer unit of peptides and proteins: a central carbon bearing an amino group, a carboxyl group, a hydrogen and a variable side chain. Twenty are genetically encoded; synthetic peptides may also incorporate non-standard or D-configuration residues.

Amphipathic

Describes a molecule with spatially separated hydrophobic and hydrophilic faces. Amphipathic helices are central to how antimicrobial peptides such as LL-37 interact with membranes, and they also explain why some peptides adsorb strongly to plastic surfaces.

Analogue

A compound structurally derived from a parent molecule by defined modification — a substituted residue, an added chain, a blocked terminus. Analogue is a structural claim, not a pharmacological one: an analogue may be more potent, less potent, or inactive.

B

Bacteriostatic water

Water containing a preservative, conventionally 0.9 per cent benzyl alcohol, which inhibits bacterial growth and so allows multiple withdrawals from one vial. It is the standard laboratory diluent for multi-draw peptide solutions. See the bacteriostatic water guide.

Batch number

The identifier tying a specific production lot to its test results. A certificate of analysis is only evidence about the vial in front of you if its batch number matches the vial label exactly; a mismatched or absent number makes the document a specimen.

Benzyl alcohol

The bacteriostatic agent in bacteriostatic water, typically at 0.9 per cent weight per volume. It suppresses microbial growth in a multi-draw vial. It is not a sterilising agent and does not compensate for poor aseptic technique during withdrawal.

Bioregulator

In this field, a very short peptide — often two to four residues — from the Khavinson research programme, proposed to influence tissue-specific gene expression. Vilon, Epitalon and Pinealon are examples. See the bioregulators guide.

Blend

A vial containing two or more peptides co-lyophilised together. Blends simplify preparation but complicate analysis, because the certificate must resolve and identify each component separately rather than reporting a single combined purity figure.

Buffer

A solution that resists pH change when acid or base is added, made from a weak acid and its conjugate base. Buffer identity affects peptide and cofactor stability measurably, so it belongs in the notebook alongside the concentration.

C

CAS number

A unique identifier assigned by the Chemical Abstracts Service, written as three digit groups such as 137525-51-0. Different salt forms and stereoisomers carry different CAS numbers, so a matching number is a stronger identity check than a matching name.

Certificate of analysis (COA)

The batch-specific document reporting what testing found: identity, purity, appearance, test methods and dates. A credible certificate names the testing laboratory and attaches the raw chromatogram and spectrum. See how to read a COA.

Chelation

Binding of a metal ion by multiple donor atoms within one molecule, forming a ring-like complex. GHK-Cu is the standard example in this field: the tripeptide chelates copper(II), and the resulting complex is what the research literature studies.

Chromatogram

The plot a chromatography detector produces: signal intensity against retention time. Peaks correspond to separated components. Reading the chromatogram — peak shape, resolution, baseline — tells you more about a batch than the single purity percentage derived from it.

Cold chain

The unbroken sequence of temperature-controlled storage and transport between manufacture and use. For lyophilised peptides the requirement is modest compared with biologics, but repeated warm excursions still accumulate, and the certificate cannot report what happened after dispatch.

Concentration

The amount of substance per unit volume of solution, most often expressed for research peptides as mg/mL. It is calculated by dividing the mass in the vial by the volume of diluent added, and it is not a statement about administration.

Counter-ion

The ion paired with a charged peptide to form a neutral salt, commonly trifluoroacetate or acetate. Counter-ions contribute mass to the vial without being peptide, which is why net peptide content can be meaningfully lower than the stated fill weight.

C-terminus

The end of a peptide chain carrying a free carboxyl group, written on the right in conventional sequence notation and given the highest residue number. Amidation converts it to a carboxamide, which blocks carboxypeptidase cleavage.

Cyclic peptide

A peptide in which the chain is closed into a ring, either head-to-tail through the backbone or through a side-chain bridge such as a disulfide or a lactam. Cyclisation constrains conformation and generally increases resistance to enzymatic breakdown.

Cryoprotectant

An excipient such as mannitol, trehalose or sucrose added before freeze-drying to protect the peptide during freezing and to give the lyophilised cake structure. Its presence is one reason a vial’s total mass exceeds its peptide mass.

D

D-amino acid

An amino acid in the mirror-image configuration to the L-form that biology normally uses. Substituting a D-residue at a protease-sensitive position is the classic way to make an analogue resistant to cleavage — triptorelin’s D-Trp at position 6 is the textbook case.

DAC (Drug Affinity Complex)

A reactive chemical group attached to a peptide so that it forms a covalent bond with circulating albumin after administration, greatly extending its functional lifetime. CJC-1295 with DAC is the standard example. See the CJC-1295 and ipamorelin guide.

Deamidation

Loss of the side-chain amide from asparagine or glutamine, converting them to aspartate or glutamate and adding roughly one mass unit. It is pH- and temperature-dependent and is one of the commonest degradation routes in stored peptide solutions.

Deletion sequence

A synthesis impurity in which one residue failed to couple, so the product is one amino acid shorter than intended. Deletion species elute close to the target peak and differ from it by the exact mass of the missing residue.

Desiccant

A moisture-absorbing material packed with lyophilised vials to keep the local atmosphere dry. Because freeze-dried peptide cakes are hygroscopic, keeping the desiccant with the vial in storage is a small habit with a measurable effect on stability.

Diluent

The liquid added to a lyophilised vial to make a solution — bacteriostatic water, sterile water, saline or a defined buffer. Diluent choice affects stability, microbial risk and assay compatibility, and should be recorded with every preparation.

Disulfide bond

A covalent sulfur–sulfur link between two cysteine residues, holding a peptide or protein in a defined fold. Reducing agents break disulfides; oxidising conditions can also cause incorrect pairing, known as scrambling, which changes structure without changing mass.

DPP-4 (dipeptidyl peptidase-4)

An enzyme that removes dipeptides from the N-terminus of susceptible peptides, including native GLP-1. Resistance to DPP-4 is the reason GLP-1 analogues substitute the second residue, most often with the non-standard amino acid Aib.

E

Endopeptidase

An enzyme that cleaves peptide bonds within a chain rather than at its ends. Endopeptidase-sensitive positions are the targets that D-amino acid substitutions and other backbone modifications are designed to protect.

Excipient

Any component of a vial other than the active compound — bulking agents, cryoprotectants, buffer salts. Excipients are legitimate and often necessary, but they mean the fill mass and the peptide mass are different numbers.

Exopeptidase

An enzyme that removes residues from one end of a peptide chain: aminopeptidases from the N-terminus, carboxypeptidases from the C-terminus. Acetylation and amidation exist largely to remove the free termini these enzymes require.

Equimolar

Present in equal numbers of moles. Because peptides differ in molecular weight, an equimolar mixture is not an equal-mass mixture, which matters when interpreting the composition of a blend stated in milligrams.

Elution

The emergence of a separated component from a chromatography column, driven by the mobile phase. In reversed-phase work, elution order broadly reflects hydrophobicity, so a change in elution order between batches is a signal worth investigating.

F

Fmoc

Fluorenylmethyloxycarbonyl, the base-labile protecting group used on the alpha-amino function in the dominant modern solid-phase peptide synthesis strategy. Fmoc chemistry replaced the older Boc approach for most research-scale synthesis because it avoids strong acid at each step.

Fragment

A defined portion of a larger natural peptide or protein, named by its residue range — for example HGH fragment 176-191. Fragments may retain some activities of the parent while lacking others entirely, which is often the point of studying them.

Free base

The uncharged, salt-free form of a compound. Molecular weights quoted for a free base differ from those of its salts, so molar calculations must use the form the certificate of analysis actually identifies.

Freeze–thaw

A stress applied every time a frozen solution is thawed and refrozen. It concentrates solutes at ice boundaries and promotes aggregation and degradation, which is why single-use aliquots are the standard defence. See the storage guide.

G

GHRH

Growth hormone-releasing hormone, the hypothalamic peptide that stimulates pituitary growth hormone release through its own receptor. Sermorelin, tesamorelin and CJC-1295 are GHRH analogues. See the secretagogues guide.

GHRP

Growth hormone-releasing peptide: a synthetic compound acting at the ghrelin receptor GHS-R1a rather than at the GHRH receptor. GHRP-2, GHRP-6, ipamorelin and hexarelin belong to this family, which is pharmacologically distinct from the GHRH analogues.

Glycoprotein

A protein carrying covalently attached carbohydrate chains. hCG and HMG are glycoprotein hormones, and because their activity depends on glycosylation as well as sequence, they are quantified by bioassay in International Units rather than by mass.

Glycosylation

The attachment of sugar chains to a protein, at asparagine residues (N-linked) or serine and threonine residues (O-linked). It influences folding, stability and circulating lifetime, and it is invisible to a simple chromatographic purity figure.

GPCR

G protein-coupled receptor: the seven-transmembrane receptor family that most peptide hormones act through, including the GLP-1, GnRH, ghrelin, melanocortin and kisspeptin receptors. Signalling proceeds through G proteins and, separately, through beta-arrestin recruitment.

Gradient elution

A chromatographic method in which the mobile phase composition changes over the run, typically increasing organic solvent. Gradient conditions determine retention times, so purity figures from different gradients are not directly comparable between laboratories.

H

Half-life

The time for a compound’s concentration to fall by half in a defined system. Reported half-lives depend heavily on species, route and assay, so figures from different studies should be compared with care rather than treated as a fixed property.

Heterodimer

A complex of two different subunits. hCG is the standard example in this glossary: a 92-residue alpha chain shared with LH, FSH and TSH, paired non-covalently with a 145-residue hormone-specific beta chain.

HPLC

High-performance liquid chromatography, the primary purity method for research peptides. In reversed-phase mode, components separate by hydrophobicity on a non-polar column, and purity is reported as the target peak’s share of total peak area.

Hydrolysis

Cleavage of a bond by water. In peptides it breaks the backbone amide link; in nucleotides such as NAD+ it attacks the glycosidic and pyrophosphate bonds. Rate rises with temperature and departs sharply from neutral pH.

Hygroscopic

Readily absorbing moisture from the air. Lyophilised peptide cakes are hygroscopic, which is why a cold vial should reach room temperature before it is opened — otherwise condensation forms directly on the material.

HPG axis

The hypothalamic–pituitary–gonadal axis: kisspeptin neurons to GnRH neurons to pituitary gonadotropins to the gonads. See the reproductive hormone peptides guide for where each compound acts.

I

IU (International Unit)

A measure of biological activity defined against an international reference preparation, used where mass does not predict activity. It has no universal milligram equivalent: the conversion differs for every substance and must come from the specific reference standard.

Impurity profile

The set of non-target species present in a batch and their relative amounts. Two batches with identical headline purity can have very different impurity profiles, which is why the chromatogram matters more than the percentage alone.

Incretin

A gut-derived hormone that potentiates insulin secretion in response to nutrients. GLP-1 and GIP are the two established mammalian incretins, and the incretin analogue class is built on them. See the GLP-1 guide.

In vitro

Literally “in glass”: experiments in cell culture, isolated tissue or purified systems rather than in a living organism. Research-use-only peptides are supplied for in-vitro laboratory and analytical work.

In vivo

Within a living organism. Published in-vivo peptide research is overwhelmingly conducted in rodents, and describing such findings is not a claim that the same effects occur in any other species.

Isoelectric point (pI)

The pH at which a peptide carries no net charge. Solubility is typically lowest at the isoelectric point, so a peptide that will not dissolve may simply be sitting at the wrong pH rather than being degraded.

K

K_d (dissociation constant)

The concentration at which half the available receptors are occupied by a ligand at equilibrium. A lower value means tighter binding. It describes affinity only, and says nothing about whether the ligand activates or blocks the receptor.

kDa (kilodalton)

One thousand daltons, the practical unit for protein masses. Short research peptides are quoted in daltons — BPC-157 at about 1,419 Da — while proteins such as somatropin are quoted in kilodaltons, at roughly 22 kDa.

Kit

A packaged set comprising vials of lyophilised material and, usually, the matching diluent. Somatropin research material is commonly supplied this way, with contents stated in International Units rather than milligrams.

L

LC-MS

Liquid chromatography coupled to mass spectrometry: components are separated in time by the chromatograph and then identified by mass. It is the strongest routine identity method for research peptides. See the purity testing guide.

Ligand

Any molecule that binds a receptor or other binding site. Ligand is a neutral term covering agonists, antagonists, inverse agonists and inert binders; it says nothing about the functional consequence of binding.

Linker

A short chemical spacer joining two parts of a molecule — for example connecting a fatty acid to a lysine side chain in an acylated GLP-1 analogue. Linker chemistry influences both attachment stability and the geometry of albumin binding.

Lyophilisation

Freeze-drying: freezing a solution, then removing water by sublimation under vacuum. It leaves a dry solid that is far more stable than the original solution and that reconstitutes readily when diluent is added.

Lyophilised

Describes material that has been freeze-dried. A lyophilised peptide arrives as a white cake or powder in a sealed vial, is hygroscopic, and should be brought to room temperature before the seal is broken.

Lyophilised cake

The solid structure left in the vial after freeze-drying. A well-formed cake is uniform and holds its shape; collapse, shrinkage or a powdery residue suggests the process or subsequent storage did not go as intended.

M

Mass spectrometry

An analytical method that ionises molecules and measures their mass-to-charge ratio. For peptides it confirms identity by matching the observed mass to the value calculated from the sequence, and it detects mass-shifted impurities such as oxidation products.

mcg (microgram)

One millionth of a gram, or one thousandth of a milligram, also written µg. Concentrations of research peptide solutions are often expressed as micrograms per 0.1 mL because that is a convenient reference volume.

Molarity

Moles of solute per litre of solution. Converting from mg/mL to molarity requires an accurate molecular weight, and using a free-base weight for a salt form — or the reverse — introduces a systematic error into every reported concentration.

Molecular weight

The mass of one mole of a compound, in grams. For peptides it is calculated from the sequence and any modifications. Average and monoisotopic values differ, and a certificate should state which convention its mass spectrometry result uses.

Monoisotopic mass

The mass calculated using the most abundant isotope of each element, rather than the isotope-weighted average. High-resolution mass spectrometers report monoisotopic values, so a small discrepancy against an average molecular weight is expected, not an error.

Mole

The SI unit for amount of substance, containing a fixed number of entities. Because assays respond to numbers of molecules rather than to mass, molar concentrations are the meaningful comparison when two compounds of different weight are studied side by side.

Multi-draw vial

A vial from which more than one withdrawal is intended, which is why a preserved diluent such as bacteriostatic water is used. Each entry through the stopper is a contamination opportunity, so technique and record-keeping matter more than with single-use preparations.

N

NAD+

Nicotinamide adenine dinucleotide, a dinucleotide coenzyme rather than a peptide, acting both as a redox carrier and as a consumed substrate for sirtuins, PARPs and CD38. See the NAD+ research guide.

Net peptide content

The proportion of a vial’s mass that is actually peptide, as distinct from counter-ions, residual water and excipients. It is a different measurement from chromatographic purity, and a batch can score highly on one and modestly on the other.

Nootropic

A descriptive category for compounds studied for effects on cognition, attention or memory. It is a research label rather than a regulatory or pharmacological class. See the Semax and Selank guide.

N-terminus

The end of a peptide chain carrying a free amino group, written on the left in conventional notation and numbered residue one. Acetylation caps it; pyroglutamate formation cyclises it; aminopeptidases attack it when it is free.

Nonapeptide

A peptide of nine residues. The naming series runs di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- and decapeptide, after which chains are usually described simply by their residue count.

O

Oligopeptide

A short peptide, conventionally of roughly two to twenty residues. The boundary with “polypeptide” is a matter of convention rather than chemistry, and different sources place it in slightly different places.

Orthogonal protection

A synthesis strategy using protecting groups removable under mutually independent conditions, so one can be taken off without disturbing another. It is what makes selective side-chain modification — cyclisation, labelling, acylation — practical during solid-phase synthesis.

Oxidation

Loss of electrons; in peptides most often the conversion of methionine to methionine sulfoxide, adding sixteen mass units, or the oxidation of cysteine and tryptophan. Light, air and oxidising buffer components all accelerate it.

P

PARP

Poly(ADP-ribose) polymerase, a family of enzymes that consume NAD+ to build ADP-ribose chains on acceptor proteins during the DNA damage response. PARP activity is one of the main drains on cellular NAD+ described in the ageing literature.

PEGylation

Covalent attachment of polyethylene glycol chains to a peptide, increasing hydrodynamic size and slowing clearance. PEG-MGF is the standard example in this catalogue, distinguished from unmodified MGF by exactly this modification.

Peptide

A chain of amino acids joined by peptide bonds. The distinction from a protein is conventional — usually drawn around fifty residues, or by whether the chain adopts a defined tertiary fold — rather than reflecting any difference in chemistry.

Peptide bond

The amide linkage formed between the carboxyl group of one amino acid and the amino group of the next, with the loss of a water molecule. Its partial double-bond character makes it planar, which constrains how a peptide can fold.

pH

The negative logarithm of hydrogen ion activity, measuring how acidic or basic a solution is. It governs peptide charge, solubility and degradation rate, and it should be recorded alongside buffer identity for any quantitative preparation.

Pharmacophore

The arrangement of chemical features required for a molecule to be recognised by its target and produce a response. Identifying the pharmacophore is what allows a long natural peptide to be shortened to an active fragment.

Potency

The concentration of a compound needed to produce a given effect, usually expressed as EC50 or IC50. A more potent compound achieves the same effect at a lower concentration; potency is separate from the maximal effect achievable.

Preclinical

Research conducted in cells, tissues or animals rather than in humans. Describing what preclinical work reported is a statement about the literature, not a prediction about any outcome in people.

Purity

The share of chromatographic peak area attributable to the target peptide, typically by reversed-phase HPLC with ultraviolet detection. It answers “how much of the peptide present is the right peptide”, not “how much of the vial is peptide”.

Pyroglutamate

A cyclised glutamine or glutamate residue at a peptide’s N-terminus, abbreviated pGlu. It occurs naturally in GnRH and blocks aminopeptidase attack; it can also form spontaneously as a storage artefact in peptides beginning with glutamine.

Q

Quality control (QC)

The testing applied to a batch to confirm it meets its specification — identity, purity, appearance, water content. Quality control is batch-level evidence; quality assurance is the system that makes such evidence trustworthy over time.

Quaternary structure

The arrangement of two or more folded polypeptide chains into a functional complex. hCG’s alpha and beta subunits form a heterodimer, and the complex rather than either chain alone is the active hormone.

R

Racemisation

Unintended conversion of an L-amino acid to its D-form during synthesis, producing a diastereomeric impurity with the same mass as the target. Because mass spectrometry cannot distinguish it, stereochemical purity requires a separate analytical approach.

Receptor

A protein that binds a signalling molecule and converts that binding into a cellular response. Most peptide hormones act at G protein-coupled receptors, though the growth factor peptides act at receptor tyrosine kinases instead.

Reconstitution

Adding a measured volume of diluent to a lyophilised vial to return the material to solution at a known, recorded concentration. See the reconstitution guide and the concentration calculator for the arithmetic.

Residue

An amino acid once incorporated into a peptide chain, so called because forming the peptide bond removes a water molecule. Residue masses, not free amino acid masses, are what a sequence-based molecular weight calculation sums.

Retention time

How long a component takes to pass through a chromatography column under stated conditions. It is a useful identity check within one method but is not transferable between laboratories using different columns or gradients.

RP-HPLC

Reversed-phase HPLC, in which a non-polar stationary phase retains hydrophobic components while a polar mobile phase carries polar ones through. It is the default separation mode for research peptide purity analysis.

RUO (research use only)

A supply category meaning the material is intended solely for laboratory research and analytical work. It is not a medicine, must not be supplied or used for human or veterinary purposes, and cannot be used for diagnosis or treatment.

S

Salt form

The ionic form in which a peptide is isolated, most often as a trifluoroacetate or acetate salt. Salt form changes formula weight and hygroscopicity, so it must be known before any molar concentration is calculated from a mass.

Secretagogue

A compound that causes a gland to release its hormone, rather than being that hormone. Growth hormone secretagogues stimulate endogenous release from the pituitary and are therefore mechanistically distinct from administering the hormone itself.

Sequence

The order of amino acid residues in a peptide, written N-terminus to C-terminus in either three-letter or single-letter code. Sequence plus any stated modifications is what fully defines a synthetic peptide’s identity.

Shelf life

The period a batch is expected to remain within specification under stated storage conditions. It is conditional on those conditions being met, so a shelf-life figure carries no information about material stored differently.

Solubility

The maximum amount of a compound that will dissolve in a given solvent at a given temperature and pH. Peptide solubility varies enormously with charge, and material that resists dissolving is often at or near its isoelectric point.

SPPS (solid-phase peptide synthesis)

The method Merrifield introduced in 1963, in which the growing chain stays anchored to an insoluble resin while reagents are washed through. It is how essentially all synthetic research peptides are made today.

Sterile water

Water that has been sterilised but contains no preservative. It suits single-use preparations, but because nothing suppresses microbial growth after the first entry it is a poor choice for a vial intended for multiple withdrawals.

Stock solution

A concentrated solution prepared once and diluted as needed for individual experiments. Preparing a stock and recording its concentration precisely is what makes downstream dilutions traceable and reproducible.

T

TFA (trifluoroacetic acid)

The acid used both in solid-phase synthesis cleavage and as a chromatographic ion-pairing agent, which is why so many research peptides are isolated as trifluoroacetate salts. Residual TFA contributes mass and can affect sensitive cell-based assays.

Tetrapeptide

A peptide of four residues. Epitalon (Ala-Glu-Asp-Gly) and several Khavinson bioregulators fall into this class, which is short enough that the whole sequence is often used as the compound’s informal name.

Third-party testing

Analysis performed by a laboratory independent of the manufacturer and the supplier. Independence matters because it separates the party with a commercial interest in the result from the party generating it.

Tripeptide

A peptide of three residues. GHK, the copper-binding tripeptide Gly-His-Lys, is the best-known example in cosmetic peptide research and is normally studied as its copper complex GHK-Cu.

Truncation

Loss of one or more residues from an end of a peptide, whether by incomplete synthesis or by enzymatic or chemical degradation. Truncated species show as separate peaks with masses that differ by known residue increments.

U

U-100 syringe

A graduated syringe marked in one-hundredth divisions of a millilitre, so one hundred units correspond to 1 mL. In laboratory work the graduations are read purely as volume markings for measuring solution.

Ultraviolet detection

The most common HPLC detection mode for peptides, usually at 214 nm where the peptide bond absorbs, or 280 nm where aromatic residues do. Detection wavelength affects apparent peak areas and so belongs on the certificate.

Unit

An unqualified “unit” is ambiguous: it may mean an International Unit of biological activity, an enzyme activity unit, or a syringe graduation. Always record which meaning applies rather than the bare number.

V

Vial

The sealed glass container holding lyophilised material, closed with an elastomeric stopper and an aluminium crimp with a flip-off cap. The stopper is designed to be pierced by a needle rather than removed.

Validation

Documented demonstration that an analytical method does what it claims — that it is specific, linear, accurate and reproducible over the range used. An unvalidated method can produce a precise number that means very little.

Viscosity

Resistance to flow. Highly concentrated peptide solutions can become noticeably viscous, which affects pipetting accuracy and is one practical reason to prepare a moderate stock concentration rather than the maximum achievable.

W

Water content

Residual moisture in a lyophilised cake, usually measured by Karl Fischer titration. Higher residual water accelerates hydrolysis and deamidation during storage, so a low, measured value is a genuine quality signal on a certificate.

Working solution

A diluted preparation made from a stock and used directly in an experiment. Working solutions are generally less stable than the stock and should be prepared close to the time of use rather than held.

Wholesale

Supply in bulk quantities, typically to institutional or repeat purchasers under tiered pricing. GenoPept’s terms are set out at the bulk and wholesale page; research-use-only conditions apply identically at any quantity.

X, Y and Z

X-ray crystallography

A structural method that determines atomic positions from the diffraction pattern of a crystal. It is how receptor–peptide complexes are resolved, and it underpins most published statements about how a peptide sits in its binding pocket.

Yield

The proportion of theoretical product actually obtained from a synthesis. In solid-phase synthesis, small per-step losses compound across many couplings, which is why long peptides are harder and more expensive to make at high purity.

Zwitterion

A molecule carrying both positive and negative charges but no net charge overall. Amino acids and many peptides exist as zwitterions at physiological pH, which explains their water solubility and their pH-dependent behaviour in chromatography.