Molecular Structure Explorer
TB-500
Structure of the compound covered in this guide.
Verified structure pending review
Last reviewed: October 2026 · Cleared Peptides research team
Research use only. TB-500 (Thymosin Beta-4): Research Guide is supplied for laboratory research. It is not a drug, food, cosmetic, or dietary supplement. It is not FDA-approved. It is not for human or veterinary administration. This page does not give a dose or a method of administration. A study cited on this page describes that study’s own test article. It does not make this lot an approved medicine. To check a fact, open the PubMed or DOI link, confirm the authors and year, and match the paper’s compound name, CAS number, or sequence to the specification table. The full method is on the research desk page. Identity and purity for a lot are only what that lot’s certificate of analysis reports. An HPLC percentage is not a sterility result and not an endotoxin result unless the certificate prints those tests.
TB-500 is the name commonly used by research suppliers for Thymosin Beta-4 (Tβ4), a 43-amino-acid, N-terminally acetylated peptide. Tβ4 is one of the most abundant intracellular peptides and the principal G-actin-sequestering molecule in many cell types, which makes it a fundamental reference compound in cytoskeleton research.
In this guide:
TB-500 Structure and Identifiers
| Name | Thymosin Beta-4 (TB-500) |
|---|---|
| Synonyms | Tβ4; Thymosin β4 acetate |
| CAS number | 77591-33-4 |
| PubChem CID | 16132341 |
| Molecular formula | C212H350N56O78S |
| Molecular weight | ≈4963.4 g/mol |
| Length | 43 amino acids, N-acetylated (Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES) |
| Physical form | Lyophilized white powder |
Note: some suppliers use “TB-500” for a short synthetic fragment (e.g. Ac-LKKTETQ) rather than the full-length peptide. Cleared Peptides’ TB-500 is the full 43-residue Thymosin Beta-4, confirmed by mass spectrometry on each lot.
Actin-Binding Function
Tβ4 binds monomeric G-actin in a 1:1 complex and inhibits its polymerization into F-actin, maintaining a pool of unpolymerized actin in the cell. The central LKKTETQ motif is the core actin-binding region and the subject of extensive structure–function work.
In-Vitro Research Applications
- Actin polymerization and cytoskeletal-dynamics assays
- Cell-migration and adhesion assays
- Angiogenesis-signaling models in endothelial cells
- Studies of the N-terminal Ac-SDKP tetrapeptide fragment
Available formats: TB-500, BPC-157 + TB-500 blend, GLOW and KLOW. COAs are posted on our COA page.
Research materials referenced in this guide
Analytical testing notes for Thymosin Beta-4 (TB-500)
Thymosin Beta-4 (TB-500) is identified in this guide as CAS 77591-33-4, formula C212H350N56O78S, listed mass ≈4963.4 g/mol. An identity test compares a measurement with those values. A mass spectrum is the usual measurement for a peptide. FTIR, when a certificate uses it, is a supporting infrared fingerprint and is less specific for closely related sequences.
For Thymosin Beta-4 (TB-500), routine chemical characterization is reversed-phase HPLC for area-percent purity and mass spectrometry for identity against the formula and mass in the table above. Oxidizable residues (cysteine, methionine, tryptophan) and deamidating residues (asparagine, glutamine), when the sequence contains them, are typical related-impurity questions for the chromatogram and the mass spectrum.
HPLC purity for this material is an area-percent result at the wavelength and gradient the laboratory states, commonly ultraviolet detection near 214 nm on a reversed-phase column. The instrument is a gradient pump, injector, column oven, and UV or diode-array detector. That percentage is not the number of milligrams in the vial. Water, acetate, trifluoroacetate, and other UV-silent material can dominate the gross weight while the purity figure stays high. Net peptide content, from an assay or amino-acid analysis, is the separate result to read when the certificate reports it.
A sterility test and an endotoxin test are not included in a chemical purity result. The compendial sterility test is a culture method (USP <71>): membrane filtration or direct inoculation into fluid thioglycollate medium and soybean-casein digest medium, incubated for 14 days. A PCR sterility screen uses a thermal cycler to detect microbial DNA and is a different method. The endotoxin test (USP <85> LAL, or USP <86> recombinant Factor C) reports endotoxin units with an incubating reader or a cartridge reader. Use a result only when that method is printed on the lot certificate. One published example in this catalog states that the report does not cover microbial contamination or endotoxins. The full description of equipment, standards, and how US laboratory accreditation works is in peptide analytical testing. Lot records are on the COA page.
Frequently Asked Questions
Is TB-500 the same as Thymosin Beta-4?
TB-500 is a supplier name for Thymosin Beta-4. Ours is the full-length 43-residue acetylated peptide, CAS 77591-33-4.
What does Thymosin Beta-4 do in cells?
In cell biology it sequesters G-actin, regulating the pool of actin available for filament assembly.
Is TB-500 for human use?
No. It is supplied for laboratory research use only.
Written by the Cleared Peptides Research Desk, the editorial desk of Cleared Wellness Group LLC. This is not a personal profile of a physician or a scientist, and it is not a fictional author. The checking method is public on the research desk page. Last reviewed October 2026.
TB-500 research note: this specification is full-length thymosin β4
Research use only. This TB-500 material is specified as thymosin β4 for laboratory research, CAS 77591-33-4. It is not a drug, and the tissue-repair literature is not a dosing guide.
The purchasing error this field actually makes
Two different molecules circulate under overlapping nicknames. One is the 43-residue protein thymosin β4. This catalog’s table specifies that protein: N-terminally acetylated, formula C212H350N56O78S, mass about 4963.4 g/mol, CAS 77591-33-4. The other is a short synthetic fragment built on the actin-binding motif LKKTETQ, often sold acetylated. The fragment is not a rounding error of the protein. A mass spectrometer separates them immediately. A certificate that reports the fragment mass does not confirm this specification, and a certificate that reports 4963 does not confirm the fragment.
Safer, Elzinga, and Nachmias (Journal of Biological Chemistry, 1991) reported that thymosin β4 and the actin-sequestering peptide Fx are the same molecule. That paper is about the protein, not about a seven-residue fragment. PubMed 1999398. Goldstein, Hannappel, and Kleinman (Trends in Molecular Medicine, 2005) review the later literature in which the actin-sequestering protein is also discussed in tissue injury. The review is not a certificate, and its repair language belongs to the studies it cites. PubMed 16099219, DOI 10.1016/j.molmed.2005.07.004.
Actin sequestration is the mechanistic core a reader can check without borrowing clinical language. Thymosin β4 binds monomeric actin and holds a reserve of G-actin. Papers that jump from that biochemical fact to an instruction for a person have left the evidence. This page stops at the biochemical identity.
What the certificate has to show
Identity is a mass consistent with the acetylated 43-residue chain, including the single sulfur in the formula. Area-percent HPLC purity still ignores water and acetate. N-terminal acetylation changes the mass by 42 units relative to the free amino terminus. A close but unacetylated mass is a related species, not an automatic pass. The method is the same one described in the analytical testing guide.
How to verify this note
- Open Safer 1991 and confirm the subject is thymosin β4, the actin-sequestering protein.
- Match CAS 77591-33-4 and mass about 4963.4 g/mol. Reject a LKKTETQ fragment mass as proof of this item.
- Read Goldstein 2005 as a review. Read the certificate as the lot record.
Selected References
Peer-reviewed literature on the compounds discussed in this guide, listed as scientific background for laboratory researchers. Citation does not imply endorsement by the authors or any use other than in-vitro research.
- Nachmias VT. Small actin-binding proteins: the beta-thymosin family. Curr Opin Cell Biol. 1993;5(1):56-62. PubMed 8448031 · DOI
- Dedova IV, et al. Thymosin beta4 induces a conformational change in actin monomers. Biophys J. 2006;90(3):985-92. PubMed 16272441 · DOI
Laboratory note: solubility depends on salt form and solvent. This guide does not state a single solubility figure. Handling of lyophilized material is described in the peptide storage guide.
Research Use Only Notice
This guide is provided for educational and laboratory reference purposes. It summarizes published, primarily in-vitro and structural research literature and does not describe, recommend or imply any use in humans or animals. Products sold by Cleared Peptides are for laboratory research use only; they are not drugs, foods, cosmetics or dietary supplements, are not FDA-approved, and are not intended to diagnose, treat, cure, mitigate or prevent any disease. No dosing, administration or therapeutic information is provided.
