TB-500 (Thymosin Beta-4) · Research brief

Thymosin Alpha 1 vs TB 500: Two Unrelated Peptides

Real Peptides Research TeamEditorial

Updated September 30, 20269 min read

52 WORDS

Short answer

Search thymosin alpha 1 vs TB 500 and you will find page after page treating them as two grades of the same compound. They are not related. Thymosin alpha 1 is a 28-residue immune-signalling peptide; TB-500 is built on thymosin beta 4, a 43-residue actin-binding protein present in nearly every mammalian cell.

Key takeaways

Thymosin alpha 1 and thymosin beta 4 share no sequence homology; the alpha and beta labels come from isoelectric-point fractions of thymosin fraction 5, a calf thymus extract characterised in the 1970s.
Thymosin alpha 1 is 28 residues at roughly 3,108 Da under CAS 62304-98-7, while thymosin beta 4 is 43 residues at roughly 4,963 Da under CAS 77591-33-4.
Research describes thymosin alpha 1 signalling through Toll-like receptors 2 and 9 on dendritic cells, whereas thymosin beta 4 sequesters monomeric G-actin inside the cell.
The TB-500 label is applied inconsistently to both full-length thymosin beta 4 and the acetylated LKKTETQ fragment covering residues 17 to 23.
Thymosin beta-4 is named on the WADA Prohibited List under growth factors; thymosin alpha 1 is not.
Neither compound is an FDA-approved drug in the United States, and both are supplied strictly for laboratory research use.

Our team fields this question almost every week from labs placing a first order, and the confusion makes sense. The shared word thymosin implies a relationship that the chemistry simply does not support.

Thymosin alpha 1 vs TB 500: what is the actual difference?

Thymosin alpha 1 and TB-500 share a family name and nothing else. Thymosin alpha 1 is a 28-amino-acid acetylated peptide (CAS 62304-98-7) studied as a Toll-like receptor-mediated immune modulator. TB-500 derives from thymosin beta 4 (CAS 77591-33-4), a 43-amino-acid peptide studied for actin sequestration and cell migration. Verify the CAS number before procurement.

The misconception worth clearing first is the alpha and beta labelling. Those letters do not signal isoforms of a single protein the way alpha and beta interferon do; they are fractionation labels from a 1970s thymus extract, and they stuck. What follows covers where the naming came from, how the two mechanisms diverge completely, what is actually inside a vial labelled TB-500, and how regulatory and anti-doping status differ.

Where the shared name came from, and why it misleads

In the 1970s, Allan Goldstein and colleagues separated a calf thymus extract called thymosin fraction 5 and sorted the resulting peptides by isoelectric point: the alpha group below pI 5.0, the beta group between 5.0 and 7.0, the gamma group above 7.0. That is the entire basis of the naming convention. Thymosin alpha 1 and thymosin beta 4 came out of the same tube of tissue extract and received adjacent labels for reasons of acid-base chemistry, not shared biology.

The sequences settle it. Thymosin alpha 1 is Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN, 28 residues, roughly 3,108 Da, cleaved from the larger prothymosin alpha precursor. Thymosin beta 4 is 43 residues, roughly 4,963 Da, and it is not thymus-specific at all: it is among the most abundant intracellular peptides in mammalian tissue and is carried at high concentration in platelets. Align the two sequences and nothing useful appears.

The difference between thymosin alpha 1 and TB 500 therefore begins at the most basic level available. They are not homologues, not isoforms, not variants of one molecule. They are two unrelated peptides discovered in the same extract.

Two mechanisms that do not overlap

Thymosin alpha 1 acts outside the cell. Research describes it binding Toll-like receptor 2 and Toll-like receptor 9 on dendritic cells and monocytes, signalling through the MyD88 adaptor protein, and promoting dendritic cell maturation with a Th1-weighted cytokine profile that includes interleukin-2 and interferon gamma. Studies also report effects on natural killer cell cytotoxicity and on T-cell maturation. The published work clusters in infectious disease and immuno-oncology: chronic hepatitis B, sepsis and immune reconstitution, and adjunct investigation alongside cancer therapy.

Thymosin beta 4 acts inside the cell, on the cytoskeleton. Its canonical role is sequestering monomeric G-actin in a one-to-one complex, maintaining the unpolymerised actin pool a cell draws on when it migrates. The literature covers endothelial cell migration and angiogenesis, corneal and dermal repair, and cardiac injury models; the ophthalmic candidate RGN-259 carried full-length thymosin beta 4 into clinical trials for dry eye and neurotrophic keratopathy. Its N-terminal tetrapeptide, Ac-SDKP, is studied separately for antifibrotic signalling.

One is a receptor ligand. The other is a cytoskeletal binding protein. In our experience supplying research labs, once a scientist sees that framing, thymosin alpha 1 and TB 500 stop looking like alternatives to one another.

What is actually inside a vial labelled TB-500

This is where tb 500 vs thymosin beta 4 becomes a procurement problem rather than a naming quibble. TB-500 is most often described as a synthetic acetylated fragment of thymosin beta 4, the seven-residue actin-binding region LKKTETQ spanning residues 17 to 23. Plenty of material sold under the TB-500 label is instead the full-length 43-residue protein. Those are two different molecules with roughly a sevenfold mass difference, different solubility behaviour and different analytical signatures.

The most common procurement error we see is not ordering the wrong peptide. It is ordering the right name, receiving the other molecule, and then comparing results against a study that used the one you did not get. A certificate of analysis carrying HPLC purity and a mass spectrometry result resolves this in seconds, because measured mass cannot lie about which sequence is in the vial.

That is why Real Peptides runs small-batch synthesis with exact amino-acid sequencing and publishes certificates for catalog compounds, thymosin alpha 1 and TB-500 included. Nothing here is dosing, preparation or administration guidance, and we do not provide it: every compound discussed is supplied for laboratory research use only.

Thymosin alpha 1 vs TB 500: side-by-side comparison

The table below sets the two peptides against the attributes that matter when sourcing material or reading a methods section. Identity verification is the row most researchers skip and most regret skipping.

Attribute	Thymosin alpha 1	TB-500 / thymosin beta 4	Bottom line for researchers
Sequence and mass	28 residues, N-terminally acetylated, roughly 3,108 Da, cleaved from the prothymosin alpha precursor	Full-length thymosin beta 4 is 43 residues at roughly 4,963 Da; the TB-500 fragment is commonly the acetylated 7-residue LKKTETQ sequence	The mass figure on a certificate is the single fastest way to confirm which molecule arrived
Origin of the name	Named for the alpha fraction of thymosin fraction 5, a calf thymus extract separated by isoelectric point	Named for the beta fraction of the same extract, though the protein is ubiquitous in mammalian cells and abundant in platelets	The shared prefix reflects 1970s fractionation chemistry, not structural or functional kinship
Reported mechanism	Research describes binding to Toll-like receptors 2 and 9 on dendritic cells and monocytes, with downstream T-cell maturation and Th1 cytokine signalling	Sequesters monomeric G-actin in a one-to-one complex, regulating actin polymerisation and cell migration	One is studied as an extracellular immune signal, the other as an intracellular cytoskeletal regulator
Main research literature	Chronic hepatitis B, sepsis and immune reconstitution, oncology adjunct studies	Corneal and dermal repair, angiogenesis, cardiac injury models, and the ophthalmic candidate RGN-259	Almost no overlap in journals, models or measured endpoints
Regulatory status	Approved outside the United States as thymalfasin (Zadaxin) in a number of countries; not FDA-approved	No approved drug product; investigational in ophthalmology only	Neither is an FDA-approved drug in the United States, and both are research use only here
Anti-doping status	Not named on the WADA Prohibited List	Thymosin beta-4 is named on the WADA Prohibited List under growth factors	Directly relevant if the research model intersects with sport science
Identity risk at procurement	Low; one well-characterised sequence under CAS 62304-98-7	High; the TB-500 label is applied to both the full-length protein (CAS 77591-33-4) and the short fragment	Match CAS number and measured mass before comparing data across studies

What If: Sourcing and Literature Scenarios

What if a supplier lists TB-500 and thymosin beta 4 as the same product?

Treat the listing as unresolved until a certificate of analysis gives you the mass. Some suppliers use TB-500 as a catch-all for full-length thymosin beta 4; others reserve it strictly for the acetylated LKKTETQ fragment. Both are legitimate research compounds, but a result generated with one cannot be replicated with the other. The mass spectrometry trace separates them instantly: roughly 4,963 Da for the 43-residue protein against under 1,000 Da for the seven-residue fragment.

What if a paper cites thymalfasin instead of thymosin alpha 1?

Same molecule, different naming convention. Thymalfasin is the international nonproprietary name for synthetic thymosin alpha 1, marketed outside the United States as Zadaxin. Clinical literature, particularly the hepatitis B and sepsis work, tends to use thymalfasin, while preclinical papers and supplier documentation use thymosin alpha 1 or Ta1. If a database search on one name returns thin results, run it again on the other; CAS 62304-98-7 covers both.

What if two published studies both say TB-500 but report different findings?

Check what each study characterised rather than what it called the compound. Methods sections that state a molecular weight, a CAS number or the explicit residue sequence are comparable to each other; ones that only print the trade-style label TB-500 are not. This ambiguity is the largest single source of contradictory secondary summaries about thymosin beta 4 online, and it is entirely avoidable at the reading stage.

What if a certificate of analysis shows purity but no mass or CAS number?

Do not proceed on purity alone. An HPLC percentage tells you how homogeneous the material is, not what the material is. Identity requires mass spectrometry, and in a peptide family with this much naming overlap, identity is the entire question. Publicly posted certificates let a lab confirm molecular identity before a purchase order goes out rather than after the material is already on the bench.

The Uncomfortable Truth About Peptide Family Names

Here is the honest answer: asking which is better in thymosin alpha 1 vs TB 500 is a category error, roughly like asking whether a smoke alarm outperforms a door hinge. They address nothing in common. No published head-to-head comparison exists and none is likely, because there is no shared endpoint on which to compare them. The family name is a fifty-year-old artefact of how someone separated proteins from a tissue extract. Any vendor, article or forum post implying the two are interchangeable, or that one is an upgraded version of the other, has not read the sequences.

Researchers working with either compound can review the full specification for TB-500 10mg or thymosin alpha 1, read the background write-up on TB-500, check batch documentation on our certificates of analysis page, or browse the wider research peptide catalog.

Thymosin alpha 1 vs TB 500 is one of those comparisons that dissolves the moment you open the primary literature, because there is no contested ground between them to argue over. The more durable lesson is about nomenclature itself. Names inherited from mid-century fractionation chemistry carry no information about structure or function, and a family label has never been a data point. When two compounds share a prefix, the sequence and the measured mass are the only things worth trusting.

References

Peer-reviewed sources on TB-500 (Thymosin Beta-4) indexed in PubMed, listed for research context. Real Peptides supplies TB-500 (Thymosin Beta-4) for laboratory research use only.

Thymosin β4 alleviates sepsis-associated acute kidney injury by suppressing MAPK signaling pathway. Clinical science (London, England : 1979), 2026. PMID 42417058. doi:10.1042/CS20261084
Sprayable bioadhesive microcarriers loaded with Tβ4-Engineered ADSC exosomes for diabetic wound healing. Bioactive materials, 2026. PMID 42383202. doi:10.1016/j.bioactmat.2026.06.024
Thymosin beta 4 as an Alzheimer disease intervention target identified using human brain organoids. Stem cell reports, 2025. PMID 40816274. doi:10.1016/j.stemcr.2025.102601
Mechanistic study of the Tβ4/SLC7A11 signaling pathway regulating breast cancer evolution. Cellular signalling, 2025. PMID 40912522. doi:10.1016/j.cellsig.2025.112111
Thymosin β4 Regulates Tissue Inflammatory Response in Mouse Nonalcoholic Fatty Liver Disease by Promoting Macrophage M2-Type Polarization. Journal of inflammation research, 2025. PMID 40322536. doi:10.2147/JIR.S492814
Injectable Thymosin β4-Modified Hyaluronic Acid Hydrogel with Exosomes for Stem Cell Homing and Neuronic-Angiogenic-Osteogenic Coupled Cranial Repair. ACS nano, 2025. PMID 40528381. doi:10.1021/acsnano.4c10386
Secreted Expression of Thymosin β4 from Pinctada fucata in Pichia pastoris and Its Biological Activity. Biology, 2025. PMID 40427742. doi:10.3390/biology14050553
Thymosin β4 and the anti-fibrotic switch. International immunopharmacology, 2023. PMID 36580759. doi:10.1016/j.intimp.2022.109628

Build a pack

Researching more than one compound?

Build a multi-vial pack and the discount applies automatically as you add doses.

Start a pack

Questions

Thymosin alpha 1 is a 28-amino-acid acetylated peptide (CAS 62304-98-7) that research describes as signalling through Toll-like receptors 2 and 9 on dendritic cells and monocytes. TB-500 is based on thymosin beta 4 (CAS 77591-33-4), a 43-amino-acid peptide whose canonical function is sequestering monomeric G-actin inside the cell. They share no sequence homology and appear in completely separate bodies of research literature.

Not always, and that is the core of the confusion. TB-500 is most commonly described as a synthetic acetylated fragment of thymosin beta 4 covering residues 17 to 23, the LKKTETQ actin-binding region. A great deal of material sold as TB-500 is instead the full-length 43-residue protein, so the only reliable way to know which one you have is the molecular weight reported on the certificate of analysis.

Compare the CAS number and the measured mass on the certificate of analysis against the reference values. Thymosin alpha 1 sits at roughly 3,108 Da under CAS 62304-98-7, and full-length thymosin beta 4 at roughly 4,963 Da under CAS 77591-33-4. HPLC purity alone confirms homogeneity, not identity, so a mass spectrometry result is the part of the certificate that answers the question.

Neither is an FDA-approved drug in the United States. Synthetic thymosin alpha 1 is approved in a number of other countries under the name thymalfasin (Zadaxin), and thymosin beta 4 has been investigated in ophthalmic clinical trials, but in the United States both are supplied for laboratory research use only. FDA reviews of bulk substances used in compounding have grouped both peptides among substances raising significant safety concerns.

No. They bind different targets, act in different cellular compartments and have been studied against entirely different endpoints, so substituting one for the other invalidates any comparison to the source literature. Thymosin alpha 1 work centres on immune signalling models, while thymosin beta 4 work centres on actin dynamics, cell migration and tissue repair models.

These compounds are sold to researchers, laboratories and institutions for in vitro and preclinical research use only, and they are not sold for human or veterinary consumption. Pricing varies by compound, vial size and batch, so the product page and the accompanying certificate of analysis are the reference points for both specification and cost.

No. Real Peptides supplies research-use-only compounds and does not provide dosing, preparation or administration guidance of any kind. What we do publish is the analytical documentation a lab needs to plan its own work: sequence, molecular weight, CAS number, HPLC purity and mass spectrometry identity confirmation on each certificate of analysis.

Thymosin beta-4 is named on the WADA Prohibited List under the growth factors category and is prohibited at all times. Thymosin alpha 1 is not listed as a prohibited substance. This is one of the few practical consequences of the alpha versus beta distinction that reaches outside the laboratory, and it is worth confirming against the current year's list before designing any sport science research.

Both were isolated from thymosin fraction 5, a calf thymus extract characterised in the 1970s, and the peptides within that extract were grouped by isoelectric point: alpha below pI 5.0, beta between 5.0 and 7.0, gamma above 7.0. The naming records a separation technique, not a structural family. Thymosin beta 4 is not even thymus-specific, since it occurs in nearly all mammalian cell types and is abundant in platelets.

Thymosin alpha 1 has the deeper clinical record, largely because it is an approved product outside the United States as thymalfasin and has been studied in chronic hepatitis B, sepsis and oncology adjunct settings. Thymosin beta 4 clinical work is narrower and concentrated in ophthalmology, notably the RGN-259 candidate investigated for dry eye and neurotrophic keratopathy. The short TB-500 fragment specifically has far less published clinical characterisation than either.

RESEARCH USE ONLY · NOT EVALUATED BY THE FDA