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This glossary defines terms researchers encounter when reading peptide literature, certificates of analysis, and laboratory protocols. Entries are listed alphabetically and focus on the chemistry, analytics, and handling vocabulary used in a research setting. Where a fact is settled, a source is cited; where a claim is not established in the literature, that is stated plainly.

For worked reconstitution math, see the reconstitution calculator. For a one-page summary of the handling vocabulary below, see the research cheat sheet.

How to read the evidence grades used on Peptigo

Several entries below reference an evidence grade. Peptigo uses a simple A–D scale to describe how much published human data exists for a compound. The grade describes the weight of evidence reported in studies, not any outcome, claim, or suitability for any use.

Grade What the literature contains
A Multiple human or clinical studies reported.
B Limited human data, or strong animal data, reported.
C Mainly animal or in-vitro (cell-based) studies reported.
D Theoretical or mechanistic interest only; little or no direct study reported.

Glossary of terms

Acetate salt

A salt form in which acetate ions act as the counterion that balances the positive charge on a peptide. Acetate is obtained by an additional ion-exchange step after synthesis and is often preferred over the trifluoroacetate (TFA) form left by Fmoc cleavage. See counterion and net peptide content (Peptide Limited; Pharmaceuticals, MDPI/PMC).

Aliquot

A precisely measured portion divided from a larger sample for separate storage or analysis. Dividing a reconstituted stock into aliquots lets a researcher thaw only what is needed, leaving the rest frozen and limiting freeze–thaw exposure that can degrade or aggregate proteins (Labguru; PMC).

Amino acid

The building-block molecule of peptides and proteins, carrying an amino group and a carboxyl group. Amino acids join by condensation to form chains, releasing one water molecule per bond (StatPearls, NCBI).

Amino acid residue

An amino acid after it has been incorporated into a chain. Because the linking reaction removes part of each amino acid’s structure, the units within a peptide are properly called residues rather than free amino acids (StatPearls, NCBI).

Bacteriostatic vs. bactericidal

A bacteriostatic agent stops bacteria from multiplying; a bactericidal agent kills them. The distinction explains why bacteriostatic water preserves a solution against growth rather than sterilising it (Pfizer Medical).

Bacteriostatic water (BAC water)

Sterile, non-pyrogenic water for injection containing 0.9% (9 mg/mL) benzyl alcohol as a bacteriostatic preservative, supplied in multiple-dose containers. The benzyl alcohol does not kill bacteria outright but inhibits their growth, which is relevant where a vial is accessed more than once (Pfizer Medical; DailyMed).

Certificate of Analysis (COA)

A document issued by a manufacturer or laboratory recording test results for a specific batch, used to confirm identity, purity, and conformity to specification. A typical COA reports identity, purity and impurity data (often by HPLC), content, and, for sterile material, microbiological or endotoxin results (Dedecke; Wikipedia).

Counterion

An ion that balances the net charge of a peptide so the isolated material is neutral overall. The two most common counterions in synthetic peptides are trifluoroacetate (TFA) and acetate; the choice affects how much of a vial’s mass is peptide versus salt (Peptide Limited; PMC).

Endotoxin

A lipopolysaccharide (LPS) from the outer membrane of gram-negative bacteria, and a type of pyrogen. Endotoxin levels are reported on a COA for material intended for sterile laboratory work and are measured by the LAL assay (FDA; Wikipedia).

Fmoc

9-Fluorenylmethoxycarbonyl, a protecting group placed on the alpha-amino position of an amino acid during solid-phase synthesis. The Fmoc strategy is favoured because the group is removed under mild basic conditions, typically with piperidine (Wikipedia; LibreTexts).

Freeze–thaw cycle

One round of freezing and then thawing a stored sample. Repeated cycles can mechanically stress and denature or aggregate proteins, which is why dividing stock into aliquots is standard practice (PMC; Labguru).

Gauge (needle)

A number describing the outer diameter of a needle on the Birmingham (Stubs) Wire Gauge scale. The scale is inverse: a higher gauge number is a thinner needle, because the number historically counted how many times wire was drawn through progressively smaller dies (International Filter Products).

GHRH (growth hormone-releasing hormone)

A hypothalamic peptide that stimulates the pituitary to release growth hormone. GHRH and its analogues are referenced in the literature as one of the two main receptor pathways through which growth-hormone secretagogues act (Wikipedia).

GLP-1 (glucagon-like peptide-1)

An incretin hormone secreted by intestinal L-cells. In published research GLP-1 is described as augmenting glucose-dependent insulin secretion from pancreatic islets, the basis of the “incretin effect” (StatPearls, NCBI). This entry describes what studies report about the endogenous hormone; it is not a statement about any product or use.

Half-life (t½)

The time required for the concentration of a substance to fall to half of its starting amount. After roughly four half-lives only about 6% remains. Half-life relates directly to volume of distribution and inversely to clearance (StatPearls, NCBI).

HPLC (high-performance liquid chromatography)

An analytical separation technique that partitions compounds between a stationary phase (column packing) and a liquid mobile phase. Reversed-phase HPLC is the most frequently described method for determining the purity of synthetic peptides, often paired with mass spectrometry (PubMed; AltaBioscience).

HPLC purity

A purity figure derived from an HPLC run, expressed as the area of the main peptide peak as a percentage of the total peak area on the chromatogram. It is a relative measure of chromatographic purity and is distinct from net peptide content (Spartan Peptides; PubMed).

Incretin

A gut-derived hormone released after eating that enhances glucose-dependent insulin secretion. GLP-1 is one of the principal incretins described in the literature (StatPearls, NCBI).

IU (International Unit)

A unit that measures the biological activity or potency of a substance rather than its mass. There is no single IU-to-mass conversion; each substance has its own factor set by international consensus (for example, 1 IU of vitamin D equals 0.025 mcg). See mcg (Britannica; Wikipedia).

LAL assay (Limulus amebocyte lysate)

An in-vitro test that detects and quantifies bacterial endotoxin using lysate from horseshoe crab amebocytes, which react with lipopolysaccharide. It is the standard method for endotoxin figures on a COA (Wikipedia; FDA).

Lyophilised (freeze-dried)

Describes material from which water has been removed by sublimation under vacuum from the frozen state, in three stages: freezing, primary drying (sublimation), and secondary drying. Removing water limits hydrolysis, oxidation, and microbial growth, so many peptides are supplied as a lyophilised powder for later reconstitution (Manufacturing Chemist; Chameleon Peptides).

Mass spectrometry (MS)

A technique that detects and identifies molecules by their mass-to-charge (m/z) ratio. For peptides, MS confirms molecular weight and can help verify sequence; HPLC combined with MS is widely described as the standard approach to purity and identity assessment (Thermo Fisher; Wikipedia).

mcg (microgram)

A unit of mass equal to one millionth of a gram (0.001 mg); also written µg. Unlike IU, a microgram measures quantity of material, not biological activity (Britannica).

m/z (mass-to-charge ratio)

The value a mass spectrometer measures: an ion’s mass divided by its charge number. A molecule of mass 1000 carrying one added proton appears at m/z 1001; carrying two protons it appears near m/z 501 (ScienceDirect).

Net peptide content

The percentage of a vial’s mass that is actually peptide, the remainder being counterions and bound moisture. It can be determined by amino acid analysis and is generally lower than the HPLC purity figure because it accounts for salt and water (AmbioPharm; Peptide Limited).

Peptide

A chain of amino acid residues joined by peptide bonds. Sources commonly describe peptides as chains of roughly 2–40 residues, with longer chains termed polypeptides and chains of about 50 or more residues termed proteins; the cut-offs are conventional rather than absolute (Wikipedia; StatPearls, NCBI).

Peptide bond

The covalent amide bond linking the carboxyl group of one amino acid to the amino group of the next, formed with the loss of one water molecule (condensation). It is the backbone linkage of every peptide and protein (Wikipedia; StatPearls, NCBI).

Pyrogen

A fever-inducing substance; bacterial endotoxin (LPS) is the most common pyrogen of concern in sterile preparations. Pyrogen and endotoxin testing are used to characterise material destined for sensitive laboratory applications (FDA).

Reconstitution

The laboratory step of dissolving a lyophilised powder in a defined volume of liquid (such as sterile or bacteriostatic water) to make a solution of known concentration. The chosen volume sets the concentration, so reconstitution is the basis for any downstream dilution math. Use the reconstitution calculator for worked figures (Chameleon Peptides).

Reversed-phase HPLC (RP-HPLC)

The HPLC mode most used for peptides, employing a non-polar C18 or C8 column and a polar mobile phase (typically water and acetonitrile with trifluoroacetic acid). It separates peptides chiefly by hydrophobicity (AltaBioscience; PubMed).

RUO (Research Use Only)

A label category for products in the laboratory research phase that are not represented as effective for diagnosis. The U.S. statement reads “For Research Use Only. Not for use in diagnostic procedures.” RUO material is not for human or veterinary use and is intended only for laboratory research (FDA).

Secretagogue

A substance that stimulates another cell or gland to secrete. A growth-hormone secretagogue, for example, is described in the literature as a molecule that prompts the pituitary to release growth hormone via the ghrelin/GHS receptor or the GHRH receptor (Wikipedia; PubMed).

Sequence

The order of amino acid residues along a peptide chain, read from the N-terminus to the C-terminus and commonly written with one- or three-letter amino acid codes. Sequence defines a peptide’s identity (Wikipedia).

Solid-phase peptide synthesis (SPPS)

A method, introduced by R. B. Merrifield, that assembles a peptide one residue at a time on an insoluble resin, repeating deprotection and coupling cycles before the finished chain is cleaved and purified. It is the dominant route to synthetic research peptides (Wikipedia; Biotage).

Sterile filtration (0.22 micron)

Passing a solution through a membrane with 0.22-micron pores to remove bacteria and particulates by physical exclusion. USP/EP recognise 0.22 µm as a sterilising-grade pore size because most bacteria are larger (about 0.5–5 µm) (Sterlitech; Industrial Pharmacist).

Telomerase

A ribonucleoprotein enzyme that synthesises the repetitive TTAGGG DNA sequences making up telomeres, the protective caps at chromosome ends. It comprises an RNA template and a catalytic protein subunit (TERT). Elizabeth Blackburn, Carol Greider, and Jack Szostak shared the 2009 Nobel Prize in Physiology or Medicine for this work (Britannica; NobelPrize.org).

TFA (trifluoroacetate) salt

The counterion most often left on a peptide after Fmoc-based synthesis, because trifluoroacetic acid is used in the cleavage step. TFA counterions are heavier than acetate, so a TFA-salt vial holds slightly less peptide by mass; for a peptide with several basic residues, TFA can make up roughly 15–25% of the total weight. See counterion and net peptide content (Peptide Limited; PMC).

Research-use-only disclaimer

All products referenced by Peptigo are sold for laboratory research use only (RUO). They are not for human or veterinary use, not drugs, not foods, and not for diagnostic, therapeutic, or cosmetic use. Nothing in this glossary is medical advice or a usage or dosing direction; the entries define vocabulary and laboratory technique only and describe what published studies report. Researchers are responsible for handling materials safely and in compliance with applicable laws and institutional policies.

Sources