Thymosin Alpha-1

Overview

Thymosin alpha-1 is a 28-residue peptide originally isolated from thymus tissue and studied as an immunomodulator. It is one of the few compounds in this library whose activity is directed at the immune system itself rather than at a metabolic, endocrine or structural target.

We do not stock it. It is documented partly for that distinct mechanism and partly to clear up a naming problem that affects a compound we do sell.

Chemical identity

• Also known as: thymalfasin, Tα1
• Sequence: Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn
• CAS number: 62304-98-7
• Molecular formula: C₁₂₉H₂₁₅N₃₃O₅₅
• Molecular weight: 3108.3 g/mol
• Classification: Thymic peptide, immunomodulator
• Length: 28 residues, N-terminally acetylated

The composition is unusual. There is no sulfur in the formula — no cysteine, no methionine — and no aromatic residues at all: no tryptophan, tyrosine or phenylalanine. Nine residues are acidic against four basic, giving a net charge around −5. It is a small, strongly anionic, chemically plain peptide with very little in it that can degrade.

Two thymosins that are not related

This needs stating clearly, because the names invite exactly the wrong inference.

Thymosin alpha-1 and thymosin beta-4 — the latter sold as TB-500 — are not variants of one another, not members of a structural family, and not functionally related.

• Thymosin alpha-1: 28 residues, 3,108 g/mol, derived from prothymosin alpha, immunomodulatory.
• Thymosin beta-4: 43 residues, 4,963 g/mol, a separate gene product, binds actin monomers and governs cytoskeletal dynamics.

The shared name is historical. Both were first identified in thymosin fraction 5, a partially purified extract of thymus tissue prepared in the 1960s and 70s, and the components of that fraction were labelled alpha, beta and gamma by their chromatographic behaviour. Those letters describe where a peptide came off a column, not what it is.

The alpha and beta thymosins were subsequently shown to be entirely distinct molecules from different precursors with unrelated functions. The naming stuck anyway.

The practical consequence: a study, a supplier listing or a summary referring simply to “thymosin” is ambiguous, and the two compounds are not interchangeable in any respect. Check which is meant.

Where it comes from

The thymus is where T cells mature and are selected, and it was long suspected of releasing soluble factors that direct that process. Work from the 1960s onward, principally by Allan Goldstein and colleagues, sought to isolate them — producing thymosin fraction 5 and, from it, the individual peptides.

Thymosin alpha-1 is generated by proteolytic cleavage from a larger precursor, prothymosin alpha, which is widely expressed rather than confined to the thymus.

Mechanism of action

The reported mechanism concerns Toll-like receptor signalling, particularly TLR2 and TLR9 — pattern-recognition receptors through which innate immune cells detect microbial material.

Published work describes thymosin alpha-1 acting on dendritic cells through those receptors, promoting their maturation and influencing the direction of the T-cell response that follows. Downstream effects reported include increased T-cell differentiation and activity, and modulation of cytokine production.

The important structural point is that this is not a compound acting on its own tissue targets. It acts on immune cells, which then act on everything else — a signal into a system rather than an effect on an organ. That makes its effects context-dependent in a way that a receptor agonist’s generally are not: what it does depends on the state of the immune system receiving the signal.

Regulatory status

Thymosin alpha-1 is approved as a prescription medicine in a substantial number of countries, marketed as thymalfasin for indications including chronic hepatitis B and C and as an immune adjuvant, and it appears on the World Health Organization’s essential medicines list in some contexts.

It is not approved in the United States, where it has been through clinical investigation without securing approval.

That split is worth noting for what it does and does not mean. Approval in many jurisdictions indicates a substantial dossier exists and regulators have found it persuasive. Absence of US approval indicates one particularly demanding regulator has not. Both facts are informative, and citing either alone gives a misleading picture.

Handling and storage

• Chemically robust. No cysteine, no methionine, no tryptophan — nothing oxidation-prone, nothing photosensitive, no disulphide to maintain. Among the more forgiving peptides documented here.
• Highly water-soluble, given the acidic residues and absence of hydrophobic bulk.
• Lyophilised storage: sealed, refrigerated; freeze for long-term storage.
• Reconstitution: add diluent slowly down the vial wall and allow to dissolve undisturbed.

Purity and analytical verification

Two points, one shared with another compound here and one specific.

N-terminal acetylation is part of the natural molecule rather than a stabilising addition, exactly as for thymosin beta-4. A synthesis omitting it produces a peptide 42 Da lighter, which mass spectrometry resolves easily. A measured mass consistent with 3,108 confirms the acetyl group is present; one near 3,066 does not.

The absence of aromatic residues creates the same detection problem described for BPC-157. With no tryptophan or tyrosine, this peptide does not absorb usefully at 280 nm, so HPLC must run at 214 nm where the peptide bond absorbs — a less selective wavelength at which solvents and non-peptide contaminants also register. A purity figure obtained that way is doing harder work than the same number on a peptide with a strong chromophore, and it is worth asking which wavelength was used.

References

• Goldstein AL, Guha A, Zatz MM, et al. Purification and biological activity of thymosin, a hormone of the thymus gland. Proceedings of the National Academy of Sciences, 1972. PMID 4505657
• Romani L, Bistoni F, Gaziano R, et al. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through Toll-like receptor signaling. Blood, 2004. PMID 14982877
• King R, Tuthill C. Immune modulation with thymosin alpha 1 treatment. Vitamins and Hormones, 2016. PMID 27450734

Summary

Thymosin alpha-1 (thymalfasin) is a 28-residue N-terminally acetylated peptide, CAS 62304-98-7, molecular formula C₁₂₉H₂₁₅N₃₃O₅₅, molecular weight 3,108.3 g/mol, cleaved from the precursor prothymosin alpha. It acts as an immunomodulator through Toll-like receptor signalling on dendritic cells, influencing T-cell maturation and response — a signal into the immune system rather than an effect on tissue. Despite the shared name it is unrelated to thymosin beta-4: the two were named for the thymic extract they were isolated from, not for any shared structure or function. It is approved in many countries though not in the United States. We do not stock it.

This page is provided for research reference. Compounds described in this library are for laboratory research use only, are not drugs, foods or cosmetics, and may not be used for any purpose other than in vitro or non-human laboratory research.