Thymosin Alpha-1 vs Thymosin Beta-4: Not the Same Peptide

01 / Overview

Shared name, unrelated molecules

Thymosin alpha-1 and thymosin beta-4 are unrelated peptides. They share the word "thymosin" only because both were first identified in thymosin fraction 5, a crude extract of calf thymus studied in the 1960s and 1970s. Thymosin alpha-1 is a 28-residue peptide studied for its effects on immune signaling; thymosin beta-4 is a 43-residue peptide best known as the main actin-sequestering molecule in many cells.

Where does each peptide come from?

Thymosin alpha-1 was isolated and sequenced in 1977 [1]. It is the N-terminal fragment of a larger precursor, prothymosin alpha, encoded by the PTMA gene, and it is acetylated at its N-terminus. Its synthetic form carries the international nonproprietary name thymalfasin and is registered as a prescription medicine in several countries outside the United States [3].

Thymosin beta-4 is encoded by the TMSB4X gene. In 1991 it was shown to be identical to Fx, a peptide that binds monomeric actin and keeps it from polymerizing [2]. That actin-binding role, not immune signaling, is the central theme of its literature.

How different are the two structures?

They differ in length, sequence and mass. Thymosin alpha-1 has 28 residues and an average molecular weight of about 3108.3 Da. Thymosin beta-4 has 43 residues and a molecular weight of about 4963 Da. There is no sequence family linking them.

Where does TB-500 fit?

TB-500 is neither of the two full peptides. In supplier catalogs it denotes Ac-LKKTETQ, the acetylated fragment covering residues 17 to 23 of thymosin beta-4, with a molecular weight of about 889 Da. It has no relationship to thymosin alpha-1. A mass spectrometry result distinguishes all three immediately: roughly 889 Da, 3108 Da and 4963 Da.

Why does the confusion matter for research material?

Because the names are close, catalog listings, search results and even laboratory request forms occasionally swap them. Checking the stated sequence, the number of residues and the observed mass on the analytical report is the reliable way to confirm which molecule a vial contains.

Frequently asked questions

Is thymalfasin the same as thymosin alpha-1?

Yes. Thymalfasin is the nonproprietary name of synthetic thymosin alpha-1.

Is TB-500 the same as thymosin beta-4?

No. TB-500 is a seven-residue fragment of thymosin beta-4, not the 43-residue peptide.

Does FLASK list both?

FLASK lists Thymosin Alpha-1 and TB-500 as separate materials. Full-length thymosin beta-4 is not currently listed.

Key facts

Thymosin alpha-1 28 residues, N-acetylated · C129H215N33O55 · 3108.3 Da · CAS 62304-98-7 · INN thymalfasin
Thymosin beta-4 43 residues, N-acetylated · C212H350N56O78S · about 4963 Da
TB-500 Ac-LKKTETQ, residues 17-23 of thymosin beta-4 · C38H68N10O14 · 889.0 Da
Genes Alpha-1 derives from prothymosin alpha (PTMA); beta-4 is encoded by TMSB4X

Footnotes & references

Source list

References

Goldstein AL et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proc Natl Acad Sci U S A. 1977;74(2):725-9. PMID: 265536.
Safer D et al. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. J Biol Chem. 1991;266(7):4029-32. PMID: 1999398.
Goldstein AL et al. From lab to bedside: emerging clinical applications of thymosin alpha 1. Expert Opin Biol Ther. 2009;9(5):593-608. PMID: 19392576.

Read the specification and the record

Use the lot record and testing pages for the source analytical documentation.