By BioLabs Research · Last reviewed: October 8, 2026
TB-500 is a catalog name for a short synthetic peptide related to thymosin beta-4 (Tβ4), a naturally occurring 43-residue peptide [1]. When analytical chemists examined a product sold as TB-500, they identified it as Ac-LKKTETQ: the N-acetylated fragment matching residues 17–23 of Tβ4 [4]. BioLabs Research lists TB-500 as this fragment, supplied for laboratory research only.
TB-500 peptide identity at a glance
| Property | TB-500 (catalog listing) | Thymosin beta-4 (full length) |
|---|---|---|
| Sequence | Ac-LKKTETQ (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH) | 43 residues; full sequence in UniProt P62328 |
| Relation | Tβ4 residues 17–23, N-acetylated | Parent peptide |
| Molecular formula | C38H68N10O14 | C212H350N56O78S |
| Molecular weight | 889.0 g/mol | 4963 g/mol |
| PubChem CID | 62707662 | 45382195 |
| Form supplied | Lyophilized powder | Not sold by BioLabs Research |
Values are from PubChem [5] and UniProt [1]. "TB-500" is used loosely across the market, so confirm the sequence and mass on the MS report for your lot.
Where the actin-binding motif sits
Tβ4 binds single actin molecules (G-actin) and keeps them from assembling into filaments, a process called actin sequestration [1]. In 1991 it was shown to be the same molecule as Fx, a previously described actin-sequestering peptide [2]. Mutational work later mapped part of its actin-binding site to a short motif at residues 17–22 (LKKTET), with lysine 18 among the residues that contact actin [3]. The TB-500 fragment, residues 17–23, spans this motif.
Research context
UniProt summarizes the documented role of Tβ4 as organizing the cytoskeleton [1]. Laboratory studies have used full-length Tβ4 and engineered variants of it to map which residues carry its actin-binding activity [3]. These are findings about molecular mechanism. They are not evidence of safety or efficacy in people.
TB-500 vs thymosin beta-4
- Thymosin beta-4: the full native peptide, 43 residues, about 4963 g/mol.
- TB-500: a synthetic 7-residue fragment matching residues 17–23, about 889 g/mol.
They are not interchangeable in experimental design, and a mass spectrometry result settles which one is in the vial. For a longer walkthrough, see TB-500 vs thymosin β4: which sequence is on the vial and TB-500 and thymosin β4: fragment vs full-length identity.
How to verify a TB-500 lot
A lot's certificate of analysis (COA) should let you check four things:
- Mass spectrometry (MS). The observed mass should match the stated sequence: about 889 Da for Ac-LKKTETQ. A result near 4963 Da describes full-length Tβ4.
- HPLC chromatogram. Purity as area percent at a stated wavelength, with the method identified.
- Lot number and test date. These tie the document to the exact vial you hold.
- Testing laboratory. The certificate should name the lab that ran the analysis. Where a COA is described as third-party, that lab should be independent of both the manufacturer and the seller, and any accreditation it cites, such as ISO/IEC 17025, can be checked in the accreditation body's public directory.
Lot COAs are available on request and are being added to our COA library. For a field-by-field walkthrough, see how to read a peptide COA; for a wider checklist, see how to verify a peptide supplier.
Storage and safety data
TB-500 ships as a sealed, lyophilized solid. Its safety data sheet lists storage at 2–8 °C or below, in the original sealed vial, protected from light and moisture. Download it from the SDS library.
Frequently asked questions
What is TB-500?
TB-500 is a synthetic peptide, Ac-LKKTETQ: an N-terminally acetylated seven-residue fragment matching residues 17–23 of mature thymosin beta-4 (UniProt P62328). Its formula is C38H68N10O14 and its molecular weight about 889.0 g/mol (PubChem CID 62707662). It appears in the analytical literature as a research compound.
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a naturally occurring 43-residue peptide of about 4963 g/mol. TB-500, as characterized in the analytical literature, is Ac-LKKTETQ, a synthetic 7-residue fragment matching residues 17–23, about 889 g/mol. The two are related by sequence but are not the same compound.
What is the sequence of TB-500?
Ac-LKKTETQ (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH), molecular formula C38H68N10O14 and molecular weight 889.0 g/mol per PubChem. Confirm it on the MS report for your lot.
Is TB-500 FDA approved?
No. Drugs@FDA lists no approved drug product containing TB-500 or thymosin beta-4. BioLabs Research sells TB-500 for laboratory research only, not for human or veterinary use.
How do I get a COA for a TB-500 lot?
Request it from the TB-500 product page or the contact form, with the lot number from the vial label. Lot COAs are available on request and are being added to our COA library.
View TB-500 research material →
References
- UniProt Consortium. UniProtKB P62328, Thymosin beta-4 (TYB4_HUMAN). uniprot.org/uniprotkb/P62328
- Safer D, Elzinga M, Nachmias VT. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. J Biol Chem. 1991;266(7):4029–4032. PubMed 1999398
- Van Troys M, Dewitte D, Goethals M, Carlier MF, Vandekerckhove J, Ampe C. The actin binding site of thymosin beta 4 mapped by mutational analysis. EMBO J. 1996;15(2):201–210. PubMed 8617195
- Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500 […]. Drug Test Anal. 2012;4(9):733–738. doi:10.1002/dta.1402. PubMed 22962027
- National Center for Biotechnology Information. PubChem Compound Summaries for CID 62707662 (TB-500, Ac-LKKTETQ) and CID 45382195 (thymosin beta-4). CID 62707662 · CID 45382195