GLP-2 (tirzepatide) is the name under which PepXtide lists this material. 'GLP-2' is a catalogue name, not a formal nomenclature term; the compound is tirzepatide, also known by the research code LY3298176. Anyone matching a vial to a method or a paper should work from the name tirzepatide, the sequence and the mass. It is supplied for laboratory research use only; not for human consumption.
Structure: a lipidated 39-residue peptide
Tirzepatide is a linear peptide of 39 amino acids with an amidated C-terminus. Its sequence includes non-proteinogenic α-aminoisobutyric acid (Aib) residues. A lysine side chain carries a linker attached to a fatty diacid, which makes the molecule a lipopeptide rather than a plain peptide. This acyl modification matters analytically because it changes how the compound behaves on a reversed-phase column, in solution and on surfaces, as well as changing its mass.
Structural work on the receptor-bound form shows how the peptide backbone sits in the transmembrane bundle and extracellular domain of the receptors (PMID: 35333651). A second structural study compares tirzepatide with a related peptide across the GIP, GLP-1 and glucagon receptors (PMID: 35217653). Both are useful for understanding why sequence integrity at the N-terminus is worth confirming on a certificate.
Complete-molecule mass versus backbone-only figures
A common source of confusion is that two different 'molecular weights' circulate for this compound. One is calculated for the complete molecule, including the linker and fatty diacid substituent, and is approximately 4813 Da (average mass). The other is calculated from the 39-residue backbone alone and is lower by the mass of the side-chain substituent. A backbone-only number is not wrong, but it describes a molecule that is not the one in the vial.
When comparing a certificate with a reference value, check which one is being used. Also check whether the report gives an average mass or a monoisotopic mass. High-resolution instruments typically report monoisotopic values or deconvoluted neutral masses, and these differ from the average figure by a few Da for a molecule of this size. A reading that looks 'off' by the full substituent mass usually means the wrong reference was used, not that the sample is wrong.
Receptor pharmacology as bench measurement
In vitro, tirzepatide has been characterised by receptor binding and by second-messenger readouts such as cAMP accumulation in cells expressing the GIP or GLP-1 receptor. The structural comparison literature relates these in vitro measurements to specific contacts between the peptide and each receptor (PMID: 35333651). Potency values from such assays depend on cell line, receptor expression level, assay format and the presence of albumin, which binds fatty-diacid lipopeptides. EC50 figures from different laboratories should therefore be compared only with those conditions in view. A certificate of analysis does not report receptor activity unless it says so explicitly; it addresses identity and chromatographic profile.
Confirming identity on a certificate
Two measurements carry most of the identity argument. LC-HRMS gives an accurate mass for the intact molecule, which can be compared with the calculated complete-molecule value and read for the charge-state envelope. HPLC with UV detection, run alongside a reference standard, shows whether the main peak elutes at the retention time of the standard and what other peaks accompany it. Mass alone does not distinguish isomers or sequence variants of the same composition, and retention time alone does not prove mass, so the pairing is what matters.
Bioanalytical literature shows that this lipopeptide is amenable to LC-MS/MS quantification with defined transitions and sample preparation (PMID: 41197390). That is a different purpose from batch identity testing, but it illustrates how the molecule fragments and ionises.
On a PepXtide report, read the following: the name of the third-party laboratory that ran the analysis, the Report ID or Laboratory ID, the method description, the observed mass against the calculated mass, and the chromatogram itself. A certificate describes what one laboratory measured on one sample. Some certificates are still pending, and the absence of one should be treated as absence of data, not as a result.
Handling and storage of a lipopeptide
Lyophilised lipopeptide is generally kept cold, dry and protected from light, following the storage statement that accompanies the material. Allow the sealed vial to reach room temperature before opening so condensation does not enter the powder.
For assay work, a stock solution is prepared at the bench in a solvent suited to the downstream experiment. Fatty-acid-modified peptides can adsorb to polypropylene and glass and may self-associate at higher concentrations, so low-binding tubes, recorded solvent composition and small single-use aliquots are sensible. Repeated freeze-thaw cycles are best avoided. Record the preparation date and the Report ID or Laboratory ID alongside each stock so results can be traced back to a specific certificate.
For research use only. This guide covers bench handling of laboratory research materials. It does not describe an application, benefit, dose, route or outcome, and nothing in it is guidance for use in a person or an animal. Nothing sold by PepXtide has been evaluated by the FDA.
Where this applies on the site
The certificate library
Every published certificate, scanned as the laboratory issued it.
Quality control
The method, the laboratory, and the real spread of results.
BPC-157
Has a published certificate to read against this guide.
GHK-Cu
Has a published certificate to read against this guide.
GLP-2 (Tirzepatide) 20mg
Has a published certificate to read against this guide.
Tesamorelin
Has a published certificate to read against this guide.
Glucagon
Named in this guide. Sequence and properties in the library.
GLP-2
Named in this guide. Sequence and properties in the library.