Catalogue / TB-500
TB-500
Also written as Thymosin beta-4 fragment 17-23, Ac-LKKTETQ.
The acetylated seven residue active fragment of thymosin beta-4, not the full 43 residue protein, and the distinction is the single most misrepresented point in this compound.
| Molecular formula | C38H68N10O14 |
| Average mass | 889.01 Da |
| Monoisotopic mass | 888.4916 Da |
| Residues | 7 |
| Termini | N-terminal acetyl, C-terminal free acid |
| Class | Repair and regenerative peptides |
| Determination | Peptide analysis, catalogue compound |
| Price | 341 USD |
Computed at build time from the composition shown on this page, not transcribed from a supplier datasheet.
TB-500 has an average molecular weight of 889.01 daltons and a monoisotopic mass of 888.4916 daltons. Identity is confirmed by matching the measured deconvoluted mass to that figure, and purity is reported separately by reversed-phase chromatography at 214 nm. The two numbers answer different questions and neither substitutes for the other.
| One letter | LKKTETQ |
| Three letter | Leu-Lys-Lys-Thr-Glu-Thr-Gln |
| Modifications | N-terminal acetyl, C-terminal free acid |
The formula and both masses in the table above are derived from this sequence and these terminal modifications. A reader who believes a figure is wrong can check the composition rather than take the number on trust, which is the point of publishing it this way.
A sequence is not an identity result. It is the expected composition against which a measured mass is compared, and the comparison is what appears on the certificate.
| Charge | m/z |
|---|---|
| [M+1H]+ | 889.499 |
| [M+2H]2+ | 445.253 |
These are the ions an electrospray source is expected to produce for a neutral mass of 888.4916 daltons, computed from the monoisotopic mass and the proton mass. They are what a raw spectrum should show before deconvolution.
A report that gives only a deconvoluted mass without the charge states it was derived from cannot be checked. Deconvolution is a calculation, and a calculation whose inputs are not shown is an assertion.
| Material sold as TB-500 is the seven residue fragment. Material sold as thymosin beta-4 is the full 43 residue protein at roughly five times the mass. A mass measurement separates them in one injection; a label does not. |
| The N-terminal acetyl group adds 42 daltons. A non-acetylated synthesis is a different molecule and is detected only if identity is established by mass. |
| Two lysines make the peptide strongly basic and poorly retained. A purity result from an unoptimised C18 gradient will under-report early-eluting impurities. |
Every compound fails in its own way. A generic peptide method applied without regard to these specifics produces a number that looks like a result and is not one.
Fragment peptides derived from larger endogenous proteins. Because they are fragments, a supplier can ship a shorter truncation that still looks correct on a chromatogram.
LC-MS identity with deconvolution, purity by RP-HPLC at 214 nm, and net peptide content where the delivered milligram figure matters.
Where the delivered milligram figure matters rather than the percentage, net peptide content by combustion analysis and water by Karl Fischer are added, and the certificate carries a closed mass balance instead of a single purity number.
| LC-MS identity | Measured mass |
| RP-HPLC purity | Area at 214 nm |
| Net peptide content | Milligrams |
| Water content | Karl Fischer |
| Counter-ion | Ion chromatography |
| Bacterial endotoxins | USP <85> |
What is the molecular weight of TB-500?
The average molecular weight is 889.01 daltons and the monoisotopic mass is 888.4916 daltons, computed from the sequence LKKTETQ shown on this page. Both figures are calculated rather than transcribed, so they can be checked against the stated composition.
How is TB-500 tested for purity and identity?
LC-MS identity with deconvolution, purity by RP-HPLC at 214 nm, and net peptide content where the delivered milligram figure matters. Purity describes the chromatographable fraction only and is not the same quantity as the peptide mass delivered per vial.
What goes wrong when TB-500 is analysed?
Material sold as TB-500 is the seven residue fragment. Material sold as thymosin beta-4 is the full 43 residue protein at roughly five times the mass. A mass measurement separates them in one injection; a label does not.
What does TB-500 analysis cost at ANALYTON?
Peptide analysis, catalogue compound is priced at 341 US dollars, covering the determinations described on this page. Content, safety and elemental determinations are ordered alongside and are priced separately on the price list.
Other compounds in this class
Updated 2026-09-01. Masses computed at build, not transcribed.