Thymosin alpha-1 is a defined peptide: 28 residues, acetylated at the N-terminus, with a sequence published by Goldstein and colleagues in 1977 and a mass of 3108.3. Thymalin is a name that began as a thymic extract, and the current certificate for the catalogue's Thymalin reports a single observed mass of 858.8, which is what a defined synthetic peptide looks like, not a mixture. The two share a source tissue and a syllable and very little else. This post sets them side by side, explains what each certificate reports, and clears up the third name that gets mixed in with them, thymosin beta-4. The catalogue supplies thymosin alpha-1 and Thymalin as lyophilized powders for laboratory research use only.
What is thymosin alpha-1?
A 28-residue peptide first isolated from calf thymus and sequenced in 1977. In the body it is processed from a larger precursor, prothymosin alpha, and it carries an acetyl group on its N-terminal serine. Its International Nonproprietary Name is thymalfasin, which the five-names post lists among the INNs that appear on supplier pages under older names.
Its literature is immunological. Romani and colleagues showed in 2004 that it activates dendritic cells through toll-like receptor signalling, and T-cell maturation assays are the other common setting. Those are cell-level findings in defined models, which is the level at which a research compound is characterised; the trial-data post explains why they stay at that level.
| Thymosin alpha-1 | Thymalin | |
|---|---|---|
| Nature | Defined synthetic peptide | Name from a thymic extract; certificate reports a defined peptide |
| Residues | 28 | Not stated on the product page |
| N-terminus | Acetylated serine | Not stated |
| Formula | C129H215N33O55 | Not stated |
| Mass | 3108.3 (certificate: 3108.3) | 858.8 observed (certificate) |
| INN | Thymalfasin | None |
| Precursor | Prothymosin alpha | Bovine thymus extract, historically |
| Catalogue vial | 10 mg | 20 mg |
| Current lot | TA110-0803 | THYM20-0318 |
| Certificate | COA7585, 17 Aug 2026 | COA3390, 3 Apr 2026 |
What is Thymalin, then?
Historically, an extract. The name comes from a preparation of bovine thymus described in the 1970s, from the same programme that later produced the short synthetic bioregulators covered in the Khavinson series comparison. An extract is a mixture, and a certificate for a mixture would report a distribution of masses and no single purity figure.
That is not what the current certificate reports. COA3390, issued by Bioviridian Inc. on 3 April 2026 for lot THYM20-0318, gives one observed mass by MALDI-MS, 858.8, and a purity of 99.8% by RP-HPLC at 214 nm, with content 18.79 mg against a 20 mg label and endotoxin at or below 0.05 EU/mL. A single mass at 99.8% purity is a defined compound. The honest reading is that the material sold under the Thymalin name is a synthetic peptide of that mass, and the product copy's description of the name's origin should be read as history rather than as a description of the vial. For a methods section, cite the certificate's mass and code, and do not call the material an extract, because the certificate says it is not one.
The mass itself, 858.8, is consistent with a peptide of roughly seven to nine residues. The certificate does not state a sequence, and this post does not guess one.
Why is thymosin beta-4 not in this comparison?
Because it is a different protein with a different job, and it belongs here only because suppliers confuse the three names. Thymosin beta-4 is a 43-residue actin-sequestering protein; TB-500 is the short fragment of it that the catalogue sells. Neither comes from prothymosin alpha, neither is acetylated in the same way, and neither has an immunological literature of the kind thymosin alpha-1 has. The shared surname dates from the 1960s, when the thymus fractions were numbered before their sequences were known.
| Name | Residues | Mass | Precursor | Studied for |
|---|---|---|---|---|
| Thymosin alpha-1 | 28 | 3108.3 | Prothymosin alpha | Dendritic-cell and T-cell signalling |
| Thymosin beta-4 | 43 | About 4963 | Its own gene (TMSB4X) | Actin binding |
| TB-500 | Short fragment of beta-4 | See the TB-500 page | Synthetic | Actin-binding motif studies |
| Thymalin | Not stated | 858.8 observed | Historically an extract | Bioregulator series research |
What does the thymosin alpha-1 certificate report?
Lot TA110-0803, certificate COA7585, issued 17 August 2026 against a 10 mg sample of white lyophilized powder, published unaltered on the certificate page.
| Certificate line | Result | What it tells you |
|---|---|---|
| Identity, LC-MS/MS | Thymosin alpha-1, 3108.3 | Matches the acetylated 28-mer; the unacetylated peptide would be 42 units lighter |
| Content, HPLC quantitation | 10.87 mg | Overage against the 10 mg label |
| Purity, RP-HPLC at 214 nm | 99.78% | One main peak; the one-percent post covers what the remainder usually is |
| Endotoxin | < 0.05 EU/mL | Suitable for the immune-cell assays this compound is used in, where endotoxin would be a confound; see the endotoxin post |
| Heavy metals | Conforms | On the August 2026 layout |
Endotoxin deserves emphasis for this compound in particular. Thymosin alpha-1 is studied for its effect on toll-like receptor signalling, and endotoxin is itself a toll-like receptor 4 agonist. A contaminated vial would produce the response the experiment is looking for, from the wrong molecule. A certificate line below 0.05 EU/mL is what allows the result to be attributed to the peptide.
How is a 3.1 kDa acetylated peptide handled?
It sits between the short peptides and the small proteins. Ten milligrams is 3.2 µmol; in 1 mL that is a 3.2 mM stock. The acetylated N-terminus protects one end from aminopeptidases, as the Semax amidate post explains for a smaller peptide. At 28 residues it can adsorb to plastic in dilute solutions, so working dilutions in cell-culture medium should contain serum or albumin unless the protocol excludes them. The storage guide windows apply, and the reconstituted-lifetime post gives the reasons to aliquot once and freeze.
Frequently asked questions
Is thymosin alpha-1 the same as thymalfasin?
Yes. Thymalfasin is the INN; thymosin alpha-1 is the name from the 1977 isolation. Both describe the acetylated 28-residue peptide with a mass of 3108.3.
Is Thymalin a smaller version of thymosin alpha-1?
No. The certificate's mass, 858.8, is not a fragment of the 3108.3 peptide in any obvious way, and the two come from different research programmes. Treat them as unrelated compounds that share a source tissue.
Why does the Thymalin certificate list four tests and the thymosin alpha-1 certificate five?
Layout by issue date. April 2026 certificates report identity, content, purity and endotoxin; August 2026 certificates add heavy metals. The certificate guide explains each line.
Can I use thymosin alpha-1 in a cell assay that also uses a TLR agonist as a positive control?
That is the standard design in the dendritic-cell literature, and the endotoxin line on the certificate is what makes the negative control meaningful. Record the certificate code in the methods.
Which should a study of thymic peptides choose?
The one whose identity is defined. Thymosin alpha-1 has a published sequence, an INN and a certificate mass that matches both. Thymalin has a certificate mass and a name with history behind it; a study using it should cite the certificate rather than the literature on the extract.
References
- Goldstein AL, Low TL, McAdoo M, et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proceedings of the National Academy of Sciences 1977;74(2):725-729. doi.org/10.1073/pnas.74.2.725
- 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;103(11):4232-4239. doi.org/10.1182/blood-2003-11-4036
- PubChem, National Library of Medicine. Thymosin alpha-1, CID 16130571, C129H215N33O55, 3108.3 g/mol. Read 27 September 2026. pubchem.ncbi.nlm.nih.gov/compound/16130571
Every product mentioned is sold for laboratory research use only and is not for human or animal use. Nothing on this page describes or recommends use of the material sold here in humans or animals.
