TB-500

TB-500 is the most ambiguous name in this catalogue, and the ambiguity is chemical rather than cosmetic. Two different materials are sold under it, and they differ in mass by more than a factor of five. Before anything else on this page is useful, that has to be resolved — so this monograph begins there rather than ending there.

The nomenclature problem

The name is applied commercially to both of the following:

Historically and by registry, “TB-500” denotes the heptapeptide — the acetylated fragment corresponding to residues 17–23 of thymosin β4, which is why it has its own CAS number. Reference houses index the name to the fragment. In practice, however, a large share of the research-peptide market ships full-length 43-residue thymosin β4 in a vial labelled TB-500, sometimes explicitly and sometimes silently. Some catalogues compound the problem by listing “TB500” as a synonym on the thymosin β4 record.

The consequence for anyone reading a specification: a CAS number of 885340-08-9 paired with a molecular weight near 4963 is internally contradictory, and so is the reverse. That pairing appears on competitor listings and is the fastest way to identify a specification nobody checked.

We do not publish a single CAS number or molecular weight for our TB-500 listing. The certificate of analysis for the lot states which material it is, and the certificate is the authority.

One further caution: figures of approximately 843 Da for the fragment and approximately 4921 Da for thymosin β4 circulate widely in vendor articles. Neither agrees with registry values. They should not be used.

Identity and classification

Both materials belong to the β-thymosin family. No receptor or molecular target is assigned to either in reference-supplier catalogue classification, and we make no claim about a target.

Structure

The heptapeptide. N-acetyl-Leu-Lys-Lys-Thr-Glu-Thr-Gln, free C-terminal acid. Seven standard L-residues, N-terminally acetylated, no cyclisation, no disulfide, no non-natural residues. It corresponds to residues 17–23 of the parent protein.

Full-length thymosin β4. A 43-residue N-terminally acetylated polypeptide, sequence Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES. The LKKTETQ motif sits within it at positions 17–23, which is the structural relationship between the two materials: the short one is a literal subsequence of the long one. Note the single methionine at position 6, which is present only in the full-length form and which introduces an oxidation pathway the fragment does not have.

Specification and characterisation

The analytical approach differs sharply between the two, which is a further reason the identity has to be settled first:

• Mass confirmation is the discriminating test. The two masses are so far apart that a single MS measurement settles which material is in the vial. If a certificate reports a mass, it has already answered the question.
• RP-HPLC purity. Detection at 214 nm. Neither material contains tryptophan or tyrosine, so 280 nm detection is uninformative — a point worth knowing before questioning a certificate that omits it.
• For full-length thymosin β4 only: methionine oxidation at position 6 produces a +16 Da sulfoxide. This is a real degradation route for the 43-mer and does not exist for the heptapeptide.
• For the heptapeptide: at seven residues, synthesis is straightforward and a high purity figure is comparatively easy to achieve. A 99% figure means considerably less on a heptapeptide than the same figure on a 43-residue chain, where deletion sequences accumulate.
• Net peptide content and counter-ion. Amino acid analysis and ion chromatography.

Handling and stability

Store sealed at 2–8 °C, dry, protected from light, and equilibrate in a desiccator before opening. Neither material contains cysteine, so disulfide scrambling is not a concern for either. For full-length thymosin β4, minimise oxygen exposure and repeated temperature cycling because of the methionine.

Both are supplied commonly as acetate salts, and both are highly water-soluble — the heptapeptide carries two lysines and a glutamate, and the full-length protein is unusually charged for its size.

Related compounds in this library

No close relative among the other compounds we supply. KPV is the other example here of a short peptide defined as a positional fragment of a larger parent, and the same reading discipline applies to both: a fragment name is meaningless without the residue numbers.

References

Chemical, specification and analytical sources. This list is deliberately limited to chemistry and analytical references.

• MedKoo Biosciences record 41195 — TB500 heptapeptide: CAS, formula, average and exact mass
• ChemicalBook, TB500 product property record — heptapeptide registry confirmation
• PubChem CID 45382195, thymosin β4 — formula and molecular weight
• Cayman Chemical 28605, thymosin β4 acetate — formula, mass, sequence
• ChemicalBook, thymosin β4 record — independent mass confirmation

Cosmic Aminos supplies this material as a laboratory reagent for in-vitro research use only. It is not a drug, food, cosmetic or dietary supplement, is not approved by the Food and Drug Administration for any use, and is not for human or veterinary consumption. No dosing, administration or preparation guidance is provided.