TB-500 is a name used across the research-peptide market for material related to thymosin beta-4, and that name does not map cleanly onto a single chemical registry entry. Depending on the supplier, “TB-500” has been catalogued as the full-length thymosin beta-4 molecule, as the actin-binding region of that molecule, or as a short synthetic acetylated peptide. This page documents what public registries record under the relevant identifiers and explains why the exact identity of any given lot must be read from its Certificate of Analysis rather than assumed from the market name. TB-500 is not sold on its own at livvmore; it appears only as one component of the co-formulated Wolverine (BPC-157 + TB-500) product, which carries a per-batch COA.
Compound identity and CAS registry
At least two distinct registry records circulate under the TB-500 heading, and they are not interchangeable. The full-length parent molecule, thymosin beta-4 (often written Tβ4), is a 43-residue peptide catalogued under CAS 77591-33-4 and PubChem CID 45382195, with the human sequence filed under UniProt accession P62328; several registry listings file this entry as the acetate form. Separately, the synthetic short peptide most often labelled “TB-500” in supplier catalogues, the N-acetylated heptapeptide Ac-LKKTETQ, carries its own set of identifiers: CAS 885340-08-9, PubChem CID 62707662, ChemSpider 72380051, and UNII QHK6Z47GTG. A third, looser usage describes TB-500 simply as the actin-binding region of thymosin beta-4 without pinning a single registry number.
Because these records describe different molecules, no single CAS number, formula, or sequence can be presented as the definitive identity of “TB-500” in the abstract. The only reliable identity statement for a specific vial is the one printed on that lot’s Certificate of Analysis, which names the measured molecule for that batch.
Molecular formula, weight, and structure
Two molecules sharing one market name means two formula and molecular-weight pairs appear across the registries, and they are far apart rather than being rounding variants of each other. The heptapeptide Ac-LKKTETQ (PubChem CID 62707662) is recorded with molecular formula C38H68N10O14 and a molecular weight near 889.0 g/mol. The full-length thymosin beta-4 molecule (PubChem CID 45382195) is recorded with molecular formula C212H350N56O78S and a molecular weight near 4963 g/mol, with some sources quoting approximately 4921 Da for the unmodified free peptide. The single sulfur atom in the full-length formula reflects the methionine residue present in the complete sequence and absent from the short fragment. A value near 889 and a value near 4900 identify two different compounds, so the figure on a COA is what fixes which one a given lot is.
Amino-acid sequence and modifications
The full thymosin beta-4 sequence, in one-letter notation, is SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES, a chain of 43 residues. Residues 17 through 23 of that sequence spell LKKTETQ. The short synthetic peptide marketed as TB-500 corresponds to this 17 to 23 region carried as an N-acetylated heptapeptide, written Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ); this structure was characterised in the analytical literature by Esposito and colleagues in Drug Testing and Analysis (2012). The N-terminal acetyl group is a defined structural modification of the fragment, not an impurity, and it is reflected in the heptapeptide formula and mass above.
In the research literature the LKKTETQ motif is categorised as the actin-binding region of thymosin beta-4. That classification is a literature category only and is not a statement of any outcome. One common catalogue error is worth noting: some listings describe TB-500 as a “17-amino-acid fragment,” which conflates the residue range 17 to 23 with a peptide length and does not match the seven-residue Ac-LKKTETQ structure.
Appearance, solubility, and storage
Research-grade peptide of either identity is typically supplied as a white to off-white lyophilised powder. Both the short heptapeptide and the full-length peptide are water-soluble as chemical reference materials; where a liquid diluent is referenced, it functions only as a controlled aqueous research reagent for a reference material, not as a preparation step. Held as a sealed lyophilised reference material, peptide of this class is generally kept cold and protected from light and moisture, and a solubilised reference material is protected from repeated freezing and thawing to limit degradation. The exact storage figures for any batch should follow the values recorded on its COA.
Confirming identity and purity by LC-MS
Because the TB-500 name is ambiguous at the registry level, analytical confirmation of what is actually in a vial matters more here than it does for a compound with a single unambiguous entry. The component peptides in the co-formulated Wolverine product are characterised by liquid chromatography paired with mass spectrometry, work carried out at the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core. LC-MS and high-resolution mass spectrometry measure the mass of the material and check it against the expected formula, so a lot can be verified against whichever identity it is meant to carry, the roughly 889 g/mol heptapeptide or the roughly 4963 g/mol full-length peptide, while HPLC reports the chromatographic purity. The per-batch Certificate of Analysis records the batch number, the measured identity, and the purity figure for that specific batch.
Related research peptides in the catalogue
TB-500 is available at livvmore only as one half of the co-formulated Wolverine (BPC-157 + TB-500) product; its composition and per-batch testing are documented on the Wolverine research profile. The other component of that formulation, BPC-157, has its own identity page covering its registry data and sequence. Each component is documented against a per-batch Certificate of Analysis.
For laboratory research use only. Not for human or veterinary use.
Frequently asked questions
Does “TB-500” refer to one specific molecule?
No. The name is used ambiguously in the research-peptide market. Public registries carry at least two separate records under the heading: the full-length thymosin beta-4 peptide (CAS 77591-33-4, PubChem CID 45382195) and the short N-acetylated heptapeptide Ac-LKKTETQ (CAS 885340-08-9, PubChem CID 62707662). A further usage refers only to the actin-binding region of thymosin beta-4. The identity of any specific lot is whatever its Certificate of Analysis states.
What CAS number should I expect to see on a TB-500 Certificate of Analysis?
It depends on which molecule the lot is. The short synthetic heptapeptide is registered under CAS 885340-08-9, while the full-length thymosin beta-4 peptide is registered under CAS 77591-33-4. Read the CAS number, measured mass, and sequence directly from the COA rather than inferring them from the market name.
Why are there two very different molecular weights for TB-500?
Because two different molecules share the name. The Ac-LKKTETQ heptapeptide has a molecular weight near 889.0 g/mol (formula C38H68N10O14), whereas the full-length thymosin beta-4 peptide has a molecular weight near 4963 g/mol (formula C212H350N56O78S). The gap between the two values is not a rounding difference; it distinguishes the two compounds.
Is TB-500 sold on its own at livvmore?
No. TB-500 is offered only as a component of the co-formulated Wolverine (BPC-157 + TB-500) product. That product carries a per-batch Certificate of Analysis documenting the composition and the analytical results.
How is the identity of the TB-500 component confirmed?
The component peptides in the Wolverine formulation are analysed by liquid chromatography and mass spectrometry at the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core. Mass spectrometry checks the measured mass against the expected formula, and HPLC reports chromatographic purity, with the results recorded on the per-batch COA.