Guide
TB-500 (Thymosin β4): A Research Peptide Overview
TB-500 is the name under which synthetic thymosin β4 is sold as a research peptide, and, confusingly, the name some vendors also use for a much shorter fragment of it. This overview covers what the molecule is, the cytoskeletal research it is used in, why the full-length-versus-fragment distinction matters, and how batch testing settles it. It is written strictly for laboratory research context.
What TB-500 is
Thymosin β4 (Tβ4) is a highly conserved 43-amino-acid peptide and the principal G-actin-sequestering peptide in mammalian cells. TB-500 is its synthetic form. It carries CAS number 77591-33-4, the molecular formula C212H350N56O78S, and a molecular weight of 4963.55 g/mol.
Some products sold as "TB-500" are instead a seven-residue fragment (the active-site sequence Ac-LKKTETQ, residues 17–23), which is a different molecule with a different mass. The lot described on our TB-500 page was identity-confirmed as full-length Tβ4.
As a research reference material it is supplied as a lyophilized powder and characterised by HPLC for purity, with identity confirmed against a reference standard.
Why it is studied
In the laboratory, Tβ4 is the canonical model for G-actin binding: it sequesters actin monomers, which makes it a standard tool in actin-polymerization and cytoskeletal-dynamics assays and in cell-migration studies in vitro.
It also appears in endothelial and fibroblast cell-culture models and serves as an analytical reference standard. These are in vitro research applications only, and no medical claims are made here.
Handling and storage
Lyophilized peptides are generally kept cold, dry, and out of light to preserve stability. TB-500 is stored long-term at -20°C (-4°F), protected from moisture and direct light, with original labeling retained so the batch stays traceable.
This overview does not cover preparation or use of any kind. That falls outside laboratory research reference use, and we do not provide that guidance.
Why purity and identity matter
A 43-residue peptide has many places to go wrong in synthesis, deletion sequences and oxidation of its single methionine among them, and the full-length-versus-fragment question means two products with the same name can differ by a factor of five in mass. Purity by HPLC and a confirmed identity answer two different questions, and a serious report carries both.
This is why a per-batch Certificate of Analysis, one tied to the exact lot you receive, is more useful than a generic brand-level document.
How to verify a TB-500 batch
Before relying on any batch, confirm three things: purity (an HPLC percentage), identity (a confirmation against a reference standard, by mass spectrometry or chromatographic retention-time match), and a traceable lot number with a test date. If the supplier lets you look up that batch’s report, you can match the documentation to the vial in hand.
See our guide on how to read a peptide COA for a field-by-field walkthrough.
Regulatory status: common questions
Is TB-500 FDA approved? No. Neither TB-500 nor thymosin β4 is an approved drug in the United States. It is supplied strictly as a laboratory research reference material, and nothing on this site is medical guidance.
Is TB-500 legal in the US? TB-500 is not a scheduled substance under the Controlled Substances Act. It is lawfully supplied as a reference material for laboratory research, and for no other purpose; nothing on this site should be read as a claim otherwise.
Is TB-500 banned in sport? Yes, thymosin β4 and its fragments are prohibited at all times under the World Anti-Doping Agency Prohibited List. That is a sporting-regulation fact, not a statement about any use; the material here is for laboratory research only.
Why a lyophilized vial and not another format? Reference material is quantified by mass and stability-characterised in lyophilized form, which is what a per-batch certificate can actually describe. Other formats fall outside laboratory reference use, so we do not offer them.