TB-500 (Thymosin beta-4)

TB-500 is a trade designation that is used inconsistently in the peptide trade. For analytical work that is precisely the central point: the name alone does not determine the molecular mass.

What is TB-500?

The designation TB-500 refers to thymosin beta-4 or to its actin-binding region. Thymosin beta-4 is a naturally occurring polypeptide of 43 amino acids with N-terminal acetylation and an average molecular mass of approximately 4.9 kDa. The short sequence Leu-Lys-Lys-Thr-Glu-Thr-Gln (LKKTETQ) is described as the actin-binding motif, a heptapeptide with a molecular mass in the range of approximately 0.9 kDa.

Both variants are traded under the designation TB-500: on the one hand the complete acetylated thymosin beta-4, on the other the short fragment. The two substances differ by more than a factor of five in mass. A product designation without a sequence or mass figure is therefore not analytically unambiguous.

Research context

Thymosin beta-4 is described in the cell biology literature as an actin-sequestering protein and has been the subject of preclinical investigations. An approved medicinal product does not exist. For research and comparison purposes it is relevant that publications on thymosin beta-4 cannot readily be transferred to preparations that contain only the heptapeptide motif. Which variant is actually present can only be clarified analytically.

Analytical identification

With TB-500 the mass determination is the decisive step, not the chromatography:

  • LC-MS reliably distinguishes the variants. A polypeptide of around 4.9 kDa produces a multiply charged ion series in electrospray, from which the mass is calculated by deconvolution. A heptapeptide of around 0.9 kDa, by contrast, typically shows a singly or doubly charged signal. The N-terminal acetylation of the complete peptide increases the mass by approximately 42 Da compared with the non-acetylated form and is visible in the mass spectrum.
  • RP-HPLC provides the impurity profile. A clean chromatogram, however, only proves that a dominant peak is present, not which substance that peak is.

This combination is a standard example of why purity and identity are separate questions.

Purity and analytical interpretation

Longer polypeptides such as thymosin beta-4 frequently show broader peaks in RP-HPLC than short peptides, because more conformational states and more synthesis-related by-products occur. With 43 amino acids, deletion sequences differ relatively little in retention time and can lie beneath the main peak. A high area-percent value is therefore less informative for long peptides than for short ones and should be supplemented by mass spectrometric data.

Documentation and batch traceability

Analytical documentation is only meaningful with a batch reference, a statement of method and the associated raw data. For TB-500 it should additionally state the sequence variant actually present, since the trade designation does not do so.

Storage and Stability

As a lyophilised powder, peptides of this class are to be stored dry, cool and protected from light. Common laboratory practice is storage at minus 20 degrees Celsius while avoiding repeated freeze-thaw cycles. These details refer exclusively to the handling of laboratory substances.

Further research resources

Associated catalogue products

This page serves exclusively as scientific and analytical information. It contains no dosage, application or treatment instructions. Products are not intended for use in humans or animals.