TB-500 (Thymosin β4 Fragment 17–23)
The synthetic, N-terminally acetylated heptapeptide Ac-LKKTETQ — 888.99 Da. Not the 43-residue parent protein, and not interchangeable with it.
Monograph
| Compound | TB-500 — thymosin β4 active fragment (residues 17–23) |
|---|---|
| Molecular Formula | C38H68N10O14 |
| Monoisotopic Mass | 888.99 Da |
| Sequence | Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ) |
| Residue Count | 7 (heptapeptide), N-terminally acetylated |
| Purity | ≥ 99.0% (RP-HPLC, UV 220 nm) |
| Identity Confirmation | ESI-MS, theoretical mass match including acetyl mass |
| Appearance | White to off-white lyophilized cake or powder |
| Solubility | Soluble in water and aqueous buffers |
| Storage (lyophilized) | −20 °C, desiccated, protected from light |
| Packaging | Type I borosilicate glass vial, tamper-evident seal |
| Documentation | Lot-specific COA with HPLC chromatogram and MS spectrum |
What TB-500 is
TB-500 is the synthetic, N-terminally acetylated heptapeptide corresponding to residues 17–23 of thymosin beta-4. That short stretch — Leu-Lys-Lys-Thr-Glu-Thr-Gln — is the actin-binding motif of the parent protein, which is why the fragment is studied as a discrete entity rather than as a truncated whole.
The distinction matters analytically and is frequently blurred in commercial listings. Thymosin beta-4 is a 43-residue protein of roughly 4.9 kDa. TB-500 is a 7-residue peptide of 888.99 Da. They are not interchangeable, they do not co-elute, and a COA for one does not verify the other. If a supplier quotes a molecular weight near 4,900 g/mol against a product labelled TB-500, the product is the full protein, not the fragment.
The N-terminal acetyl group is part of the definition, not an optional modification. It blocks the terminal amine, removes the positive charge at the N-terminus, and measurably shifts retention time on reverse-phase columns. A non-acetylated LKKTETQ standard is a different molecule with a mass 42 Da lower (846.97 Da); the two are easily distinguished by ESI-MS, and a supplier that does not state which form they ship has not characterised their material.
Research context
The following summarises mechanisms reported in preclinical and in-vitro literature. It is provided for scientific orientation only and does not describe any approved or established clinical application.
Actin sequestration
The 17–23 fragment binds monomeric G-actin. In cell-free systems this binding shifts the polymerisation equilibrium and is the most direct, best-characterised activity of the sequence — it does not depend on a receptor and can be measured in pure protein preparations.
Cell migration in culture
Scratch and transwell assays report increased directional migration of fibroblasts and keratinocytes exposed to the fragment, consistent with actin cytoskeletal reorganisation at the leading edge.
Cytokine modulation
Several in-vitro studies report downregulation of pro-inflammatory cytokine secretion in stimulated macrophage and epithelial cultures. The effect is concentration-dependent and varies by cell type.
Note on evidence status
Published work on TB-500 is predominantly in-vitro and rodent. The fragment has not completed Phase III human trials and is not approved as a medicine in any jurisdiction.
Analytical verification
Every lot is released against three independent checks:
- Purity — RP-HPLC. C18 column, gradient acetonitrile/water with 0.1% TFA, UV at 220 nm. Main-peak area percentage, acceptance ≥ 99.0%.
- Identity — ESI-MS. Deconvoluted mass compared against theoretical 888.99 Da. The observed mass must also confirm N-terminal acetylation; a value near 846.97 Da indicates unacetylated material and fails release.
- Appearance and solubility. Visual inspection; solubility confirmed in water.
The chromatogram and mass spectrum for your specific lot are bound into its Certificate of Analysis. Look up your lot in the COA registry.
Preparing a standard solution
This protocol is for preparing calibration standards for instrumental analysis. It is not a preparation guide for any biological or human application.
- Equilibrate. Bring the sealed vial to room temperature before opening.
- Dissolve. Add sterile deionised water or an appropriate aqueous buffer down the vial wall. Typical HPLC calibration concentrations fall between 0.1 and 1.0 mg/mL, adjusted to your method.
- Mix gently. Swirl; do not vortex. Shear and air bubbles degrade injection reproducibility.
- Filter if your method requires it. 0.22 µm PVDF or PTFE, matched to column compatibility.
- Use freshly prepared. Aqueous peptide solutions hydrolyse over time; prepare per run.
- Avoid repeated freeze–thaw. If holding a solution, aliquot once and store at −20 °C or below, protected from light.
Frequently asked questions
What is the sequence of TB-500?
Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln — written Ac-LKKTETQ. It is N-terminally acetylated, and the acetyl group is part of the specification.
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a 43-residue protein (~4.9 kDa). TB-500 is the 7-residue fragment corresponding to its residues 17–23 (888.99 Da). They differ in mass by roughly 4 kDa and are not interchangeable.
Why is the molecular weight 888.99 and not 846.97?
846.97 Da is the unacetylated heptapeptide. N-terminal acetylation adds 42.04 Da, giving 888.99 Da. Our lots are acetylated and the mass spectrum is required to confirm it.
What purity do you guarantee?
≥ 99.0% by RP-HPLC per released lot. The measured value for your lot appears on its Certificate of Analysis.
Can I view the COA before ordering?
Yes. Open the batch registry — each record lists lot number, assay date, testing laboratory, method, and measured purity.
Who performs the testing?
Independent third-party laboratories. The testing laboratory and task number are printed on each COA so the record can be cross-checked with the issuing lab directly.
How should the lyophilized powder be stored?
−20 °C, desiccated, protected from light — stable for 24 months from assay date. Ambient is acceptable during transit only.
Is TB-500 approved for human use?
No. It is not approved as a medicine, food, cosmetic, or veterinary product in any jurisdiction. It is supplied strictly as a research reference standard.
Research use only
This product is a chemical reference standard intended exclusively for in-vitro laboratory research and analytical method development. It is not a pharmaceutical, drug, food, food additive, cosmetic, or veterinary product. It has not been evaluated or approved by the FDA, EMA, MHRA, TGA, or any other regulatory authority for any human or animal application, and it must not be administered to humans or animals.
By purchasing, the buyer represents that they are a qualified researcher or institution with the facilities and training to handle biochemical reference materials safely, and that the material will be used only for lawful in-vitro investigation.