Knowledge
Peptide glossary
67 terms from peptide chemistry, analysis and lab work, briefly explained.
Basics: 8Structure and synthesis: 12Lab work and solutions: 15Analysis: 20Documentation: 5Pharmacology terms: 7
A
- Acetylation Structure and synthesis
- Adding an acetyl group, usually at the N-terminus. It raises the molecular mass by 42 g/mol. Variants such as N-acetyl Semax or N-acetyl epithalon are modified forms of the parent peptide. More →
- Aggregation Analysis
- Peptide molecules clumping together, often with hydrophobic sequences. Aggregates make solutions cloudy, and the real concentration is then unknown. More →
- Agonist Pharmacology terms
- A molecule that binds to a receptor and activates it. Dual or triple agonists activate two or three different receptors. More →
- Aib (aminoisobutyric acid) Structure and synthesis
- A non-proteinogenic amino acid with two methyl groups on the alpha carbon. It makes the neighbouring peptide bond hard to cleave. Semaglutide carries Aib at position 8 instead of alanine. More →
- Aliquot Lab work and solutions
- A portion split off from a solution, usually for single use. Aliquots avoid repeated freezing and thawing, which damages peptides in solution.
- Amidation Structure and synthesis
- Replacing the C-terminal carboxyl group with an amide. This removes a negative charge and occurs in many natural peptide hormones. Amidated peptides are often more stable against carboxypeptidases.
- Amino acid Basics
- The building block of peptides and proteins. Each amino acid has an amino group, a carboxyl group and a side chain that sets its properties. Proteins use 20 proteinogenic amino acids, and synthetic peptides often add non-natural ones such as Aib or D-amino acids. More →
- Amino acid analysis Analysis
- A method in which the peptide is fully hydrolysed and the individual amino acids are measured. It gives the peptide content, which HPLC and MS do not.
- Analogue Structure and synthesis
- A molecule that resembles a natural model but is changed on purpose, for example by swapping amino acids or adding a side chain. CJC-1295 is an analogue of GHRH, semaglutide one of GLP-1.
- Area percent Analysis
- The unit of HPLC purity: the main peak's area divided by the area of all peaks. Anything the detector does not see, such as water or salts, is not counted. More →
B
- Bacteriostatic water Lab work and solutions
- Sterile water with 0.9% benzyl alcohol. The additive inhibits bacterial growth, so an opened container can be drawn from several times. In the lab it serves as a solvent. More →
- Benzyl alcohol Lab work and solutions
- The preservative in bacteriostatic water, usually at 0.9%. It can interfere in sensitive cell experiments, where sterile water without additives is the better choice. More →
- Bioregulator Pharmacology terms
- A name for short peptides of two to four amino acids, studied mainly in Russian research, such as epithalon. In the catalogue they form their own research area. More →
C
- C-terminus Structure and synthesis
- The end of a peptide with the free carboxyl group, on the right of the sequence. Many peptides carry an amide there instead of the acid, shown as -NH2 in the sequence.
- Certificate of analysis (CoA) Documentation
- The document with the test results for one specific lot, such as identity, purity and peptide content. It applies to that lot only. More →
- Chromatogram Analysis
- The curve an HPLC run produces: detector signal over time. Each substance shows as a peak. An attached chromatogram makes a purity figure checkable.
- Counterion Analysis
- The ion that balances the charge of a peptide salt, such as trifluoroacetate or acetate. Counterions count towards the weighed mass but not towards the peptide.
D
- D-amino acid Structure and synthesis
- The mirror image of the natural L-amino acid. Proteases recognise D-amino acids poorly, which is why many synthetic peptides such as GHRP-2 or ipamorelin contain D-residues on purpose. More →
- DAC (drug affinity complex) Pharmacology terms
- A group of lysine and maleimidopropionic acid that binds covalently to albumin. It distinguishes CJC-1295 with DAC from the version without. More →
- Deamidation Analysis
- A degradation route in which asparagine or glutamine lose their amide group. The mass rises by about 1 Da. Basic pH and heat speed it up. More →
- Deletion sequence Structure and synthesis
- A synthesis by-product missing one or more amino acids. Deletion sequences are very similar to the target peptide and often appear right next to the main peak in HPLC.
- Desiccator Lab work and solutions
- A tightly closing container with a drying agent. Chilled vials can reach room temperature inside it without taking up moisture from the room air.
E
- Earlier analysis Documentation
- The test result for an older sample. It shows the quality of earlier stock, but it is not a certificate of analysis for the lot delivered today. More →
- Endotoxins Analysis
- Cell wall components of certain bacteria that can strongly distort cell experiments. They are measured with dedicated tests such as the LAL test, not by HPLC.
- ESI-MS Analysis
- Mass spectrometry with electrospray ionisation. Peptides become multiply charged, so the spectrum shows several signals for the same molecule.
- Expiry date Documentation
- The date until which a lot should meet its specification when stored as required. At Alpenpeptid it is shown on the product page next to the current lot.
G
H
- Half-life Pharmacology terms
- The time in which half of a substance is broken down or cleared. Lipidation, D-amino acids or albumin binding, as with DAC, extend it considerably in the literature. More →
- HPLC Analysis
- High-performance liquid chromatography. A sample is pumped under pressure through a separation column, and its components leave at different times. For peptides it mainly serves to measure purity. More →
- Hygroscopic Lab work and solutions
- Taking up water from the air. Lyophilisates are strongly hygroscopic. That is why a cold vial should reach room temperature before opening, so no moisture condenses. More →
I
- In vitro Lab work and solutions
- Latin for 'in glass': experiments outside a living organism, for example on cell cultures or isolated enzymes.
L
- LC-MS Analysis
- Liquid chromatography coupled directly to a mass spectrometer. Each peak gets its mass, so the target peptide and by-products can be identified. Now the usual route to an identity check.
- Lipidation Structure and synthesis
- Attaching a fatty acid to a peptide, often through a linker on a lysine side chain. The fatty acid mediates binding to albumin. Liraglutide, semaglutide and tirzepatide are lipidated peptides. More →
- Lot and lot number Documentation
- A lot is the quantity of a product from one production run. The lot number on the vial, delivery note and CoA links the material to its test documents. More →
- Lyophilisate Lab work and solutions
- The dry powder left after freeze-drying. Most research peptides are supplied as a lyophilisate in a glass vial, because they are much more stable dry than in solution. More →
- Lyophilisation (freeze-drying) Lab work and solutions
- A drying method in which the frozen solution is held under vacuum and the ice evaporates directly. The peptide is left as a loose powder without heating.
M
- MALDI-TOF Analysis
- Mass spectrometry with matrix-assisted laser desorption and time-of-flight analysis. It mostly produces singly charged ions and suits a quick mass check.
- Mass spectrometry (MS) Analysis
- A method that measures the mass-to-charge ratio of molecules. A measured mass that matches the calculated mass supports a peptide's identity. More →
- Molarity Lab work and solutions
- The amount-of-substance concentration in mol per litre. A 1 mM solution of a 1000 g/mol peptide holds 1 mg of peptide per millilitre. More →
- Molecular formula Analysis
- The number of atoms of each element in a molecule, such as C62H98N16O22 for BPC-157. The calculated molecular mass follows from it. More →
- Molecular mass and dalton Analysis
- The mass of a molecule, given in daltons (Da) or g/mol. It is calculated from the molecular formula and measured by mass spectrometry. More →
N
- N-terminus Structure and synthesis
- The end of a peptide with the free amino group. By convention it is written on the left of the sequence. Acetylation at the N-terminus protects many peptides from aminopeptidases.
O
- Oligopeptide and polypeptide Basics
- Oligopeptides consist of a few amino acids, usually up to about ten. Polypeptides are longer chains. The terms have no strict boundary and are used differently across the literature.
P
- Peptide Basics
- A chain of amino acids joined by peptide bonds. The boundary to a protein is usually put at about 50 amino acids. Short peptides are named by length: di-, tri-, tetra- or pentapeptide. More →
- Peptide bond Basics
- The amide bond between the carboxyl group of one amino acid and the amino group of the next. It forms with the loss of water. The peptide bond absorbs UV light around 214 nm, which makes HPLC detection of peptides possible.
- Peptide content Analysis
- The share of peptide in the whole weighed mass. The rest is mainly counterions and water. For peptide salts it is often between about 60 and 90%. More →
- Peptide hormone Basics
- A hormone made of an amino acid chain, such as GLP-1, GHRH or oxytocin. Many research peptides are synthetic analogues of these hormones with a modified sequence.
- Preclinical Lab work and solutions
- Research before any testing in humans, meaning in vitro work and animal models. Preclinical findings do not transfer to humans without further study.
- Protecting group Structure and synthesis
- A chemical group that blocks reactive sites during synthesis, such as Fmoc or Boc. It is removed at the end. If part of it remains, mass spectrometry shows too high a mass. More →
- Protein Basics
- A long amino acid chain, usually more than 50 residues, that folds into a defined three-dimensional structure. Many peptides are fragments or analogues of proteins or peptide hormones.
R
- Receptor Pharmacology terms
- A protein that a messenger binds to, triggering a signal in the cell. In research, peptides are often grouped by the receptor they bind, such as the GLP-1 receptor or GHS-R1a.
- Reconstitution Lab work and solutions
- Dissolving a lyophilisate in a solvent to make a solution of known concentration. The solvent depends on the peptide's sequence and charge. More →
- Research peptide Basics
- A peptide made and sold for laboratory research, for example in vitro experiments. Research peptides are not medicines and are not for use in humans or animals. More →
- Retention time Analysis
- The time after which a substance leaves the HPLC column. It depends on column, gradient and hydrophobicity, and is only comparable within the same method.
- RP-HPLC Analysis
- Reversed-phase HPLC with a non-polar column and a gradient of water and acetonitrile, usually with 0.1% trifluoroacetic acid. More hydrophobic peptides come out later. It is the standard method for peptide purity. More →
- RUO (research use only) Basics
- The label for products intended for research only. It means a product is not intended for diagnostic, therapeutic or any other use in humans or animals.
S
- Safety data sheet (SDS) Documentation
- A document on a substance's hazards, handling, storage and disposal. It is the reference for a lot's storage conditions.
- Sequence Structure and synthesis
- The order of the amino acids in a peptide, read from the N- to the C-terminus. It is written in one- or three-letter code, such as GHK or Gly-His-Lys. The sequence sets mass, charge, solubility and stability. More →
- Solid-phase peptide synthesis (SPPS) Structure and synthesis
- The standard method for making synthetic peptides. The chain grows one amino acid at a time on a resin. At the end the peptide is cleaved off, purified and lyophilised. Incomplete couplings create deletion sequences.
- Sterile water Lab work and solutions
- Germ-free water without a preservative. It suits preparations that are used straight away, or where benzyl alcohol would interfere with the experiment. More →
- Stock solution Lab work and solutions
- A concentrated solution from which working solutions are diluted. For an accurate concentration, the weighed mass is corrected by the peptide content. More →
T
- TFA (trifluoroacetic acid) Analysis
- A strong acid used in synthesis and HPLC purification. Peptides are then often present as trifluoroacetate salts. For cell work an exchange to acetate is sometimes wanted.
V
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For laboratory research use only. Not for use in humans or animals.