TB-500 (Ac-LKKTETQ): Research Reference
Research Use Only. This page is a technical reference for in-vitro laboratory research. Reserve Research compounds are not for human or veterinary use, and nothing here is guidance for administration of any kind.
In simple words
TB-500 is a short chain of 7 amino acids. It is made in a lab. It is a small piece copied from a bigger protein called thymosin beta-4.
That bigger protein holds on to actin. Actin is a building block that gives cells their shape. Scientists use TB-500 in the lab to study this.
Reserve Research sells TB-500 only for lab research. See TB-500 on our product page →
TB-500 is the research-market name for Ac-LKKTETQ (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH), an N-acetylated synthetic fragment of the protein thymosin beta-4 (Tβ4) covering residues 17–23. That seven-residue stretch is the central actin-binding motif of Tβ4, a 43-amino-acid peptide that binds and sequesters monomeric (G-) actin in cells. TB-500 has CAS number 885340-08-9, formula C38H68N10O14 and a molecular weight of about 889.0 g/mol. Full-length Tβ4 is a different, much larger molecule (CAS 77591-33-4, about 4,963.5 g/mol).
TB-500 key facts
| Name | TB-500 |
|---|---|
| Synonyms | Ac-LKKTETQ, N-acetyl thymosin β4 (17–23) |
| Compound class | Synthetic acetylated heptapeptide; fragment of thymosin β4 |
| Sequence | Ac-L-K-K-T-E-T-Q-OH (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH) |
| CAS number | 885340-08-9 |
| Molecular formula | C38H68N10O14 |
| Molecular weight | ≈889.0 g/mol (free peptide) |
| Parent protein | Thymosin β4: 43 amino acids, N-acetylated, ≈4,963.5 g/mol, CAS 77591-33-4 |
| Appearance | White to off-white lyophilized powder |
| Solubility | Water-soluble (vendor data: ≥10 mg/mL in PBS, pH 7.2) |
| Storage (lyophilized) | −20 °C, dry, protected from light |
TB-500 vs. thymosin beta-4
The two names are often used interchangeably, and that causes real confusion in spec sheets and certificates. They are different molecules:
| TB-500 (Ac-LKKTETQ) | Thymosin β4 | |
|---|---|---|
| Length | 7 amino acids | 43 amino acids |
| Sequence | Ac-LKKTETQ-OH | Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES |
| Formula | C38H68N10O14 | C212H350N56O78S |
| Molecular weight | ≈889.0 g/mol | ≈4,963.5 g/mol |
| CAS | 885340-08-9 | 77591-33-4 |
A certificate of analysis for TB-500 should report a mass near 889 g/mol. A mass near 4,963 g/mol means the vial contains full-length thymosin β4 instead.
Mechanism studied in research models
- G-actin sequestration. Thymosin β4 binds monomeric actin and keeps it from polymerizing. An actin-sequestering peptide previously called Fx was shown to be identical to Tβ4 (Safer et al., 1991).
- Actin binding measurements. Binding of Tβ4 to muscle and platelet actin was quantified, with implications for how much unpolymerized actin cells hold in reserve (Weber et al., 1992).
- Endothelial cell migration. Tβ4 increased directional migration of cultured human umbilical vein endothelial cells in Boyden-chamber assays (Malinda et al., 1997).
- The 17–23 motif. LKKTETQ sits at the centre of Tβ4’s actin-binding region, which is why this fragment was chosen for synthesis. The LKKTET core is strongly conserved across β-thymosins.
Most mechanistic literature describes full-length thymosin β4. Far fewer primary studies test the isolated Ac-LKKTETQ fragment.
Laboratory handling and storage
- Lyophilized powder: store at −20 °C, sealed and dry, away from light. Let the vial reach room temperature before opening.
- Solvent: water-soluble. Labs commonly use sterile bacteriostatic water or buffered saline for stock solutions.
- Prepared solutions: keep at 2–8 °C and avoid repeated freeze–thaw cycles.
What a TB-500 certificate of analysis should show
- Identity: mass consistent with ≈889.0 g/mol for Ac-LKKTETQ (not ≈4,963 g/mol, which is full-length Tβ4).
- Purity: chromatographic purity reported for the specific batch.
- Batch traceability: a lot number that matches the vial label.
Every Reserve Research batch is tested by an independent lab. You can look up any batch number on our COA verification page.
Frequently asked questions
What is TB-500?
TB-500 is the research-market name for Ac-LKKTETQ, a synthetic N-acetylated fragment of thymosin beta-4 (residues 17–23). This region is the protein’s central actin-binding motif.
Is TB-500 the same as thymosin beta-4?
No. TB-500 is a 7-amino-acid fragment (≈889 g/mol). Thymosin beta-4 is the full 43-amino-acid protein (≈4,963.5 g/mol). Both names are sometimes used loosely, so check the molecular weight on the certificate of analysis.
What is the CAS number for TB-500?
885340-08-9 for Ac-LKKTETQ. CAS 77591-33-4 belongs to full-length thymosin beta-4.
What is the molecular weight and formula of TB-500?
C38H68N10O14, with a molecular weight of about 889.0 g/mol.
What does thymosin beta-4 do in cells?
It binds monomeric G-actin and keeps it from polymerizing, acting as one of the cell’s main actin-sequestering proteins.
How should TB-500 be stored?
Store the lyophilized powder at −20 °C, dry and protected from light. Keep reconstituted solutions at 2–8 °C and avoid repeated freeze–thaw cycles.
Is Reserve Research TB-500 sold for laboratory research only?
Yes. It is sold strictly for in-vitro laboratory research. It is not a drug or supplement, and it is not for human or veterinary use.
Research-grade TB-500 from Reserve Research
TB-500 is supplied as a lyophilized powder in sealed vials, independently tested batch by batch, with the COA available through the product page and /verify. Related: BPC-157 reference and bacteriostatic water.
References
- Safer D, Elzinga M, Nachmias VT. Journal of Biological Chemistry. 1991;266:4029–4032. doi:10.1016/S0021-9258(20)64278-8
- Weber A, Nachmias VT, Pennise CR, et al. Biochemistry. 1992;31:6179–6185. doi:10.1021/bi00142a002
- Malinda KM, Goldstein AL, Kleinman HK. FASEB Journal. 1997;11:474–481. doi:10.1096/fasebj.11.6.9194528
- Cayman Chemical, TB-500 (acetate) product data: formula, molecular weight and solubility.
Last reviewed: October 2026. This page summarizes published laboratory literature for reference. It makes no claims about the safety or effectiveness of any compound in humans or animals.