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Research use only
· 7 min read
"TB-500" is the internet's name for two different molecules that differ in mass by a factor of five, and that confusion is built into the label itself. The defined chemical entity registered as TB-500 (CAS 885340-08-9) is a seven-residue acetylated peptide, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, with a molecular weight of about 889 g/mol. Full Thymosin Beta-4 is a 43-residue protein weighing roughly 4,963 g/mol. They are not the same molecule, they do not share a PubChem record, and most of the published research attached to the name concerns the full protein rather than the heptapeptide. Sorting out which is which is the single most useful thing a reference page can do here. Kovalabs supplies TB-500 strictly as a research reagent; everything below describes what published studies investigated, not any human use, benefit or outcome.
| Compound | TB-500 (acetylated thymosin-beta-4 fragment) |
|---|---|
| Synonyms | TB500, TB 500, Ac-LKKTETQ |
| Class | Synthetic N-acetylated heptapeptide; the actin-binding fragment of thymosin beta-4 |
| Amino-acid sequence | Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ) |
| Molecular formula | C38H68N10O14 |
| Molecular weight | 889.0 g/mol (average) |
| CAS number | 885340-08-9 |
| PubChem CID | 62707662 |
| UNII | QHK6Z47GTG |
| Supply status | Research use only - not for human or veterinary use |
The TB-500 record (PubChem CID 62707662, CAS 885340-08-9, UNII QHK6Z47GTG) describes the N-acetylated heptapeptide Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, molecular formula C38H68N10O14, average molecular weight 889.0 g/mol. That LKKTETQ sequence is the actin-binding motif of thymosin beta-4 - residues that, in the parent protein, form the contact surface for monomeric actin. TB-500 is, in effect, that motif synthesised on its own and capped with an acetyl group. There is no cysteine in the sequence, so there is no disulfide bond to maintain.
This is the trap, and it is worth being precise about because it changes which literature applies. The defined TB-500 entity is the heptapeptide above. Full thymosin beta-4 is a separate molecule with its own PubChem record (CID 45382195): a 43-residue protein, molecular formula C212H350N56O78S, molecular weight approximately 4,963 g/mol - more than five times the mass of the heptapeptide. Products sold as "TB-500" are frequently the full protein rather than the fragment, and the in-vivo research catalogued below was largely conducted on full thymosin beta-4. The practical consequence: confirm which molecule a given lot actually is against its certificate of analysis, because an 889 g/mol heptapeptide and a 4,963 g/mol protein are not interchangeable and a mass-spectrometry check distinguishes them instantly.
| Property | TB-500 (defined entity) | Thymosin Beta-4 (full) |
|---|---|---|
| Residue count | 7 (heptapeptide) | 43 (full protein) |
| Sequence | Ac-LKKTETQ | 43-residue chain (contains the LKKTETQ motif) |
| Molecular formula | C38H68N10O14 | C212H350N56O78S |
| Molecular weight | 889.0 g/mol | ~4,963 g/mol |
| PubChem CID | 62707662 | 45382195 |
| Relationship | Acetylated actin-binding fragment | The parent protein |
The thymosin beta-4 mechanism that the structural literature actually resolves is actin handling. Full thymosin beta-4 is described as the principal intracellular sequestering peptide for monomeric (G-)actin, forming a 1:1 complex that holds actin in reserve and influences the monomer-to-filament equilibrium. The LKKTETQ motif preserved in TB-500 is the part of the protein implicated in that actin contact. The biophysical characterisation is direct: De La Cruz et al. (Biophysical Journal, 2000; PMID 10777749) measured how thymosin beta-4 changes the conformation and dynamics of actin monomers in vitro. Review-level treatments of the beta-thymosin family and their actin interactions (Bubb, Vitam Horm 2003, PMID 12852258; Sun et al., Ann N Y Acad Sci 2007, PMID 17495248; Nachmias, Curr Opin Cell Biol 1993, PMID 8448031) situate the peptide in that cytoskeletal role. These describe a molecular mechanism; no human-relevant outcome is asserted from any of them.
The thymosin beta-4 literature is broad and largely concerns the full protein. Each item below is stated as study design and the named topic or endpoint only. No result, effect size or benefit is reproduced.
On doses: the cited works are mechanism and review papers and do not report a single comparable administered dose, and the in-vivo dosing literature concerns full thymosin beta-4 rather than the heptapeptide. Rather than translate or invent figures, no doses table is given here; where a specific study reports a regimen, it is in that study. This is research context, not a set of findings or instructions a reader should act on.
The notes below are general physicochemical and storage information for bench work only. They are not dosing, administration or use instructions, and nothing here describes a preparation for use in humans or animals.
TB-500 is typically supplied as a white lyophilised powder, commonly as the acetate salt. As a short, hydrophilic, cysteine-free peptide it dissolves readily in aqueous laboratory solvents and has no disulfide bond to protect. Standard short-peptide practice applies: store the sealed lyophilate desiccated, cold and out of light, frozen for long-term storage, and equilibrate to room temperature before opening; reconstitute in an appropriate aqueous solvent and aliquot to avoid repeated freeze-thaw cycles. See the reconstitution guide. The single most important bench check for this compound is identity: because "TB-500" is used for both the 889 g/mol heptapeptide and the 4,963 g/mol full protein, the lot certificate of analysis (mass and purity) is what tells you which one you actually have. Researchers working across the tissue-repair set often cross-reference BPC-157 (the two are compared in the BPC-157 vs TB-500 reference) and the copper peptide GHK-Cu, within the tissue-repair research category.
Worth being honest about the tiers. The well-established part is the chemistry: the defined heptapeptide's identity, mass and sequence (Ac-LKKTETQ, 889 g/mol, CID 62707662) are settled, as is the fact that its LKKTETQ motif is the actin-binding region of a protein that genuinely exists in cells. The middle ground is the mechanism: actin sequestration and the conformational changes it produces are characterised in vitro (PMID 10777749), with the broader role surveyed in review papers - but a cell in a dish is not a person, and most of that work concerns the full 43-residue protein, not the heptapeptide sold under this name. The weakest part is human evidence: there is essentially none specific to the 889 g/mol fragment, only mechanism and disease-context reviews of the parent protein. It is not a licensed medicine, and it has not been shown to produce defined outcomes in humans. Curiosity is warranted; certainty is not.
Kovalabs supplies TB-500 strictly as a research chemical for laboratory research use only. It is not a medicine, supplement or veterinary product, is not for human or veterinary use, and nothing on this page constitutes a medicinal, therapeutic, healing, efficacy, dosing or human-outcome claim. It has not been evaluated by the MHRA or any comparable regulator for safety or efficacy in humans or animals. The descriptions above are restricted to chemistry and to study designs and named topics, stated only as what each study investigated. Every batch is third-party tested with a certificate of analysis. Purchasers are responsible for handling, storing and using the material in compliance with all applicable laws and institutional requirements. Full terms are on the research disclaimer page.
Not exactly, and the difference matters. The defined chemical entity TB-500 (CAS 885340-08-9, PubChem CID 62707662) is a seven-residue acetylated fragment, Ac-LKKTETQ, of about 889 g/mol - the actin-binding motif of thymosin beta-4. Full thymosin beta-4 is a separate 43-residue protein (PubChem CID 45382195) of about 4,963 g/mol. Products labelled "TB-500" are sometimes the fragment and sometimes the full protein, so the lot certificate of analysis is the way to confirm which you have.
For the defined heptapeptide entity: PubChem CID 62707662, CAS 885340-08-9, UNII QHK6Z47GTG, molecular formula C38H68N10O14, average molecular weight 889.0 g/mol, sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln. Full thymosin beta-4 is the distinct record CID 45382195 (C212H350N56O78S, ~4,963 g/mol).
Actin handling. Thymosin beta-4 is described as the principal intracellular sequestering peptide for monomeric G-actin, and in-vitro biophysics has measured how it changes actin-monomer conformation and dynamics (PMID 10777749). The LKKTETQ motif retained in TB-500 is the actin-contact sequence. This is a molecular mechanism described in the literature, not a statement of any effect in humans or animals.
As bench handling of a research reagent only. The lyophilised powder is stored sealed, desiccated, cold and out of light (frozen for long-term storage) and equilibrated to room temperature before opening. It is a short cysteine-free peptide, so it dissolves readily in an appropriate aqueous laboratory solvent; aliquot to avoid freeze-thaw cycles. See the reconstitution guide. None of this is a preparation method for any use in humans or animals.
No. TB-500 is supplied as a research chemical for laboratory use only. It is not approved as a medicine by the MHRA or any comparable regulator, is not for human or veterinary use, and nothing on this page is a medicinal, therapeutic, healing or efficacy claim. See the research disclaimer for full terms.
The publication titles below are the original authors' own titles, reproduced so each citation can be verified against PubMed and the cited DOI. They are not statements, conclusions or claims by Kovalabs, and the body of this page describes each study by its design and named topic only.