Scientist viewing a protein ribbon model with a highlighted fragment, comparing a peptide fragment to the full protein in vitro
Mindful Research

TB-500 vs Thymosin Beta-4: The Fragment, the Full Protein, and the Lab Data

By: Mindful Research Team3 min read

Key takeaways

  • TB-500 is the full-length, N-acetylated thymosin beta-4 (43 residues), not the Ac-LKKTETQ fragment.
  • Identity is fixed by CAS 77591-33-4, formula C212H350N56O78S and MW ~4963 g/mol.
  • The short heptapeptide fragment and the full peptide differ ~10x in mass and are distinguishable by HPLC and MS.
  • Thymosin beta-4 is studied in vitro as a G-actin sequestering peptide in migration and angiogenesis assays.
  • For in vitro research use only.

TB-500 is the synthetic, N-acetylated form of thymosin beta-4 (Tβ4), a single-chain 43-residue peptide (CAS 77591-33-4, C212H350N56O78S, MW ~4963), studied in vitro as an actin-sequestering peptide — not the short Ac-LKKTETQ fragment it is often confused with.

Search the term "tb 500 peptide" and you will find two different molecules described as if they were one: the full-length thymosin beta-4 polypeptide, and a seven-residue fragment of it. For anyone sourcing or characterising a research material, that distinction decides what the certificate of analysis should show. This profile sets out what the compound actually is, in vitro-framed and identity-first.

What is TB-500?

TB-500 is supplied by Happy Peptides as TB-500 as a white lyophilized powder and corresponds to the full 43-amino-acid sequence of thymosin beta-4 with an acetylated N-terminus. Its catalog identity is fixed by CAS 77591-33-4, molecular formula C212H350N56O78S and a monoisotopic-scale molecular weight near 4963 g/mol. The international nonproprietary name (INN) for this peptide is timbetasin; "TB-500" and "Tβ4" are the names more common in research catalogs.

Is TB-500 a fragment or the full protein?

Both descriptions circulate because thymosin beta-4 contains a conserved actin-binding motif, the Ac-LKKTETQ sequence, within residues 17–23. Some suppliers market that short heptapeptide as "TB-500," while others — including this catalog — supply the complete 43-mer. They are not interchangeable: they differ in mass by roughly an order of magnitude, elute differently on HPLC, and give entirely different mass-spectrometry signatures. The only reliable way to know which molecule a vial contains is to read its analytical data.

Attribute Full-length Tβ4 (TB-500) Ac-LKKTETQ fragment
Residues 43 7
Approx. MW ~4963 g/mol ~889 g/mol
Catalog identity CAS 77591-33-4 n/a (fragment)

What in-vitro models is thymosin beta-4 used in?

Thymosin beta-4 is best characterised in the laboratory as a G-actin sequestering peptide: it binds monomeric actin and participates in cytoskeletal dynamics. That biochemistry is studied with scratch and cell-migration assays and with angiogenesis-pathway readouts in cultured cells. These are mechanism and assay-design contexts only; this page makes no claim about outcomes in a living organism.

How does TB-500 compare with BPC-157?

TB-500 and BPC-157 are frequently sourced together because both are studied in tissue-repair research models, but they are structurally unrelated — BPC-157 is a 15-residue pentadecapeptide, see the BPC-157 structural profile. Laboratories comparing them often also work with the two-component BPC-157, TB-500 blend and the single BPC-157 profile.

How is TB-500 handled in the lab?

As a lyophilized powder it is reconstituted for in-vitro work with a suitable solvent such as bacteriostatic water, then aliquoted. Stock concentration is expressed in mg/mL or molarity — worked through in the vial concentration-math guide — and solution behaviour is covered in the stability-in-solution notes.

Related research guides

Research-use note

All materials discussed are supplied for in vitro laboratory research use only, and are not for human or animal use.

Frequently asked questions

Is TB-500 a peptide or a fragment?

TB-500 is the synthetic, N-acetylated form of full-length thymosin beta-4, a 43-residue peptide (CAS 77591-33-4, MW ~4963), not the short Ac-LKKTETQ fragment it is often confused with. TB-500 structure

How can I tell the full peptide from the fragment?

They differ in mass by roughly ten-fold and give different HPLC retention and mass-spectrometry signatures; read the analytical data. HPLC for peptides

What is the molecular weight of TB-500?

The full-length peptide has a molecular weight near 4963 g/mol and formula C212H350N56O78S.

What assays use thymosin beta-4 in vitro?

It is studied in scratch/cell-migration and angiogenesis-pathway assays as a G-actin sequestering peptide. Cell-migration assays

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