TB-500 research peptide UK: the thymosin beta-4 fragment explained
TB-500 is the Ac-LKKTETQ fragment of thymosin beta-4, not the full protein. Its chemistry, literature, storage.
TB-500 is the research name for a short synthetic fragment of thymosin beta-4, one of the most abundant actin-binding proteins in mammalian cells. It is frequently confused with the full-length protein, sold under inconsistent specifications, and described online with claims that the published literature does not support. This guide sets out what the compound actually is, its chemistry, where it appears in the research literature, how to handle it, and how Alphex TB-500 is verified. All material is supplied for laboratory and in-vitro research only.
What TB-500 is (and what it is not)
Thymosin beta-4 (Tβ4) is a 43-residue protein found in most cell types, where its main known role is sequestering monomeric actin. TB-500 is not the whole protein. It is a synthetic heptapeptide corresponding to residues 17-23 of Tβ4, the sequence Leu-Lys-Lys-Thr-Glu-Thr-Gln (LKKTETQ), supplied with an N-terminal acetyl group: Ac-LKKTETQ. That seven-residue stretch is the actin-binding motif of the parent protein, which is why the fragment was chosen for study.
The distinction matters when reading the literature or comparing suppliers. Studies of full-length thymosin beta-4 are not studies of TB-500, and a supplier listing "TB-500" at a molecular weight near 4,963 g/mol (the full protein) is either mislabelling or selling something different. The fragment has a molecular weight of 889.0 g/mol.
Specification
- Sequence: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ), thymosin beta-4 fragment 17-23
- Molecular formula: C38H68N10O14
- Molecular weight: 889.0 g/mol
- CAS number: 885340-08-9
- Form supplied: lyophilised powder in a vacuum-sealed glass vial, acetate salt
- Purity specification: 99+% by RP-HPLC at 220 nm; identity by ESI-MS within 1 Da of theoretical mass
- Sizes: 5 mg and 10 mg vials
Where TB-500 and thymosin beta-4 appear in the literature
The parent protein has a substantial preclinical and early clinical literature; the 17-23 fragment has a much smaller one, and it is worth keeping the two apart when reviewing sources. Themes in the published work include:
- Actin dynamics. The LKKTETQ motif is the actin-sequestering region of Tβ4, and the fragment has been used in vitro to probe actin binding and cell motility.
- Tissue repair models. Full-length Tβ4 has been studied in animal models of dermal, corneal and cardiac injury; some groups have tested whether the short fragment retains activity in comparable models.
- Cell migration and inflammation markers. In-vitro work has looked at endothelial and fibroblast migration and at inflammatory signalling.
Researchers should note that a fragment retaining a binding motif does not necessarily reproduce the behaviour of the parent protein, and should design controls accordingly. Nothing in this literature establishes any use outside the laboratory.
Handling, storage and reconstitution
Lyophilised: -20 C for long-term storage, 2-8 C for short periods, protected from light and moisture. Allow the vial to reach room temperature before opening.
Reconstitution: TB-500 is water-soluble. Reconstitute in bacteriostatic water for multi-sample stocks or in sterile water or the assay buffer for single use, adding solvent slowly down the vial wall and swirling gently. Because the peptide contains two lysines and a glutamate, solubility is good across the physiological pH range.
In solution: refrigerate at 2-8 C and use within a few weeks; aliquot and freeze at -20 C for longer storage; avoid repeated freeze-thaw. Threonine and glutamine residues make the sequence somewhat susceptible to deamidation over long storage in solution, so older stocks should be re-checked or discarded for sensitive assays. See storage, reconstitution and shelf life.
Net peptide content: account for bound water and acetate counter-ion when preparing concentration-critical assays; gross vial weight is not net peptide.
How Alphex verifies TB-500
Each batch is synthesised to the Ac-LKKTETQ sequence, run on reverse-phase HPLC at 220 nm against a reference standard with a 99+% area purity threshold. The results are issued on a Certificate of Analysis carrying the batch number printed on the vial, with the chromatogram included and the testing laboratory named. Stock is UK-held with same-day dispatch before 2pm Monday to Friday. Full method: how Alphex tests every batch.
The mass-spec identity check is especially relevant for TB-500 because of the confusion with full-length thymosin beta-4 described above: an observed mass of 889 rather than 4,963 is the definitive answer to "which compound is this". If a supplier's COA does not show an observed mass, ask why.
Buying TB-500 in the UK
TB-500 is one of the compounds most often sold with a borrowed or generic COA. Before ordering, check for UK stock, a batch-matched certificate available before purchase, an independent named laboratory, and a chromatogram. The COA guide shows what a genuine document looks like and the tells of a fabricated one, and the supplier checklist covers the rest.
Frequently asked questions
Is TB-500 the same as thymosin beta-4?
No. TB-500 is a seven-residue synthetic fragment (residues 17-23) of the 43-residue protein. They differ in size by a factor of five and should not be treated as interchangeable in study design.
Why is TB-500 sometimes out of stock?
Alphex lists a batch only when a verified lot is physically in UK stock. If the product page shows sold out, the back-in-stock notification will email you when the next verified batch is vialled; we do not list stock we cannot ship the same day.
Can I request the COA before ordering?
Yes: request the in-stock batch COA and we reply with the certificate and chromatogram.
Is TB-500 legal in the UK?
It is legal to purchase and possess for laboratory research and is not a controlled substance. It has no marketing authorisation as a medicine. See UK research peptide compliance.
Alphex TB-500 is supplied for laboratory and in-vitro research by qualified researchers only. It is not authorised for human or veterinary use.
Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.
Published 6 April 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.