The words, defined.

A molecule that binds a receptor and activates it, producing a biological response. Partial agonists activate the receptor less strongly. The counterpart is an antagonist, which blocks or dampens activation.

See also: Receptor, Bioavailability

The building block of peptides and proteins. Twenty standard amino acids are encoded by human genes; a peptide's sequence of amino acids determines its shape and function.

See also: Peptide, Peptide bond

Sterile water containing a small amount of bacteriostatic preservative (typically 0.9% benzyl alcohol), used as a diluent in research settings. Contrast with plain sterile water, which contains no preservative.

See also: Reconstitution

The fraction of an administered compound that reaches circulation in an active form. Route of administration changes bioavailability dramatically, which is why results from one route cannot be assumed for another.

See also: Half-life

A laboratory document reporting which tests were performed on a specific batch and what they found. A COA only verifies the attributes it actually lists — anything not tested is not verified.

See also: HPLC, LC-MS, Purity, Endotoxin

The amount of peptide per unit of liquid, expressed as mg/mL. Concentration equals mass divided by volume, and it is the value every dose-volume calculation is built on.

See also: Reconstitution

Toxic fragments of bacterial cell walls. Endotoxin testing (often via LAL assay) measures bacterial contamination in a sample — an attribute completely separate from purity or identity.

See also: Certificate of analysis (COA), Purity

The time it takes for the amount of a compound in a system to fall by half. Reported half-lives depend on how and in which species they were measured, so they are approximate comparisons, not fixed constants.

See also: Bioavailability

High-performance liquid chromatography — a laboratory technique that separates the components of a mixture. In peptide COAs, HPLC is typically used to measure purity: what percentage of the sample is the target peptide versus impurities.

See also: Purity, LC-MS, Certificate of analysis (COA)

Liquid chromatography–mass spectrometry — combines separation (LC) with mass-based identification (MS). Unlike HPLC alone, LC-MS can confirm that a sample is actually the claimed compound, not just that it is pure.

See also: HPLC, Certificate of analysis (COA)

Freeze-dried. Peptides are usually sold as a lyophilized (dried) powder to preserve them during storage. The powder must be reconstituted with a diluent before it can be measured or studied.

See also: Reconstitution, Bacteriostatic water

A short chain of amino acids joined by peptide bonds, typically around 50 amino acids or fewer. Many hormones and signaling molecules in the body are peptides. Distinguished from proteins (longer, folded chains) and from non-peptide small molecules.

See also: Amino acid, Peptide bond

The chemical link joining two amino acids in a chain. Chains of these bonds are what make a molecule a peptide rather than a loose collection of amino acids.

See also: Peptide, Amino acid

The fraction of a sample that is the target compound, usually reported as a percentage from HPLC analysis. Purity says nothing about identity — a sample can be pure and still be the wrong compound — and percentages from different test methods are not directly comparable.

See also: HPLC, Certificate of analysis (COA), Endotoxin

A cellular protein that recognizes specific molecules — such as peptides — and triggers a response. A peptide's effects depend on which receptors it binds and how strongly it activates them.

See also: Agonist

Dissolving a lyophilized peptide powder in a liquid diluent. Reconstitution changes the concentration of the resulting solution but never the total mass of peptide present.

See also: Concentration, Lyophilized