Two words that look like variants of one another and are not. Thymulin is a specific nine-residue peptide with a published sequence, a formula and a PubChem entry. Thymalin is the trade name of a thymus extract. Searches for "thymalin vs thymulin" are common enough that the question deserves a direct answer, and the answer leads somewhere the catalogue has to be honest about: the vial sold here as Thymalin carries a certificate whose single observed mass is the mass of thymulin.
This post sets out what each name refers to, what the certificate reports, and what a matching mass can and cannot establish. The thymosin alpha-1 versus thymalin post covers the other comparison people draw, with a 28-residue peptide that is neither of these.
What is thymulin?
A nonapeptide: pyroglutamyl-alanyl-lysyl-seryl-glutaminyl-glycyl-glycyl-seryl-asparagine, usually written pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn. The N-terminal glutamate is cyclised to pyroglutamate, which is why the sequence begins pGlu. Formula C33H54N12O15, average mass 858.9.
It was first described as facteur thymique sérique, FTS, by Jean-François Bach's group, who isolated it from pig serum and reported its sequence in Nature in 1977. A later paper from the same group, in PNAS in 1982, reported that the peptide's activity in their rosette assay depended on bound zinc, and that the zinc-free peptide was inactive in that assay. That zinc dependence is the single most-cited fact about thymulin and the reason the free peptide and the zinc complex are treated as different reagents in the literature.
Thymulin has a defined identity. A certificate for it can report a mass, 858.9, and that mass can be checked.
What is Thymalin?
A name, not a sequence. Thymalin is the Khavinson programme's polypeptide extract of calf thymus, described from the 1970s onward and summarised in Anisimov and Khavinson's 2010 review as the starting material from which the short synthetic thymic peptides, including vilon, were designed. An extract is a mixture. It has a composition, not a formula, and a certificate for it would report a profile, not one mass.
So the two names refer to different kinds of thing: one is a molecule, the other is a preparation.
What does the catalogue certificate report?
COA3390, issued by Bioviridian Inc. on 3 April 2026 for lot THYM20-0318, the lot in every vial sold under the Thymalin name.
| Test | Method | Result |
|---|---|---|
| Identity | MALDI-MS | 858.8 observed |
| Purity | RP-HPLC, 214 nm | 99.8% |
| Content | Gravimetric against label | 18.79 mg against 20 mg |
| Endotoxin | LAL | ≤ 0.05 EU/mL |
A single mass, 858.8, with a single main peak at 99.8% of area. That is the profile of one defined peptide, not of an extract. The thymosin alpha-1 versus thymalin post made this observation when it was written and stopped there, noting that the mass is consistent with a peptide of seven to nine residues and declining to name one. This post goes one step further, because the step is arithmetic.
What does 858.8 match?
Thymulin's formula, C33H54N12O15, has an average mass of 858.9. The certificate observed 858.8. The difference is within what MALDI-MS reports.
| Candidate | Mass | Match |
|---|---|---|
| Thymulin, pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn | 858.9 | yes |
| A thymus extract | no single mass | no |
| Thymosin alpha-1 | 3108.3 | no |
| Vilon, Lys-Glu | 275.3 | no |
What this establishes: the vial contains a single defined peptide whose mass is the mass of thymulin, and does not contain an extract. What it does not establish: the sequence. A mass of 858.8 is consistent with thymulin; it is also, in principle, consistent with other nine-residue arrangements of the same residues, or with different residues that happen to sum to the same mass. MALDI-MS reports the molecular ion, not the fragment ladder; a tandem LC-MS/MS identity, like the ones newer lots on the site carry, would narrow it further. The LC-MS post explains the difference.
The honest reading is this: the name on the vial is the programme's name for an extract, and the certificate describes a defined peptide that is almost certainly thymulin. A researcher who needs thymulin should treat the certificate mass as the relevant fact and the name as a label. A researcher who needs the extract called Thymalin will not find it in this vial, or in any vial that reports a single mass.
What follows for a research design?
Three practical points.
- Zinc. If what is in the vial is thymulin, Dardenne's 1982 result applies: activity in the classic assays depended on bound zinc, and the peptide as lyophilized is the metal-free form. Any assay reproducing that literature needs to add zinc under controlled conditions, and to record it.
- Molar amount. 20 mg at 858.9 g/mol is 23.3 micromoles; the measured content, 18.79 mg, is 21.9. The molarity post has the method.
- Handling. Pyroglutamate at the N-terminus is stable. Asparagine at the C-terminus and the Gly-Gly pair are sites for slow deamidation and for hydrolysis at extremes of pH; keep stocks cold and near neutral. The reconstituted shelf-life post has the general rules. No cysteine, methionine or tryptophan, so no oxidation or light problem.
Why state all this on a supplier's own site?
Because the alternative is a product page that trades on a name and lets the buyer discover the mass. The certificate is published for the opposite reason. If a lot's certificate says something the catalogue name does not, the certificate wins, and the page should say so. The post on reading two certificates side by side and the post on what a certificate does not test for are the same principle applied elsewhere.
Frequently asked questions
Are thymalin and thymulin the same thing?
No. Thymulin is a defined nonapeptide with a published sequence and a mass of 858.9. Thymalin is the name of a calf thymus extract. The vial sold here under the Thymalin name has a certificate mass of 858.8, which is thymulin's mass.
Does the certificate prove the vial is thymulin?
It proves the vial contains one defined peptide of mass 858.8, which is thymulin's predicted mass. A single mass is strong evidence but not a sequence; tandem MS would be stronger.
Is thymulin active without zinc?
In Dardenne and colleagues' 1982 assays, no: the zinc-free peptide was inactive and activity was restored by zinc. Lyophilized peptide is the metal-free form.
Is thymulin the same as thymosin alpha-1?
No. Thymosin alpha-1 is a 28-residue acetylated peptide of mass 3108.3, with a separate literature. The comparison post covers it.
Why not just rename the product?
That is a catalogue decision for the site's owner, not something a journal post can do. What the post can do is state the certificate's finding plainly so that no buyer orders on the name alone.
References
- Bach JF, Dardenne M, Pleau JM, Rosa J. Biochemical characterisation of a serum thymic factor. Nature 1977;266(5597):55-57. doi.org/10.1038/266055a0
- Dardenne M, Pleau JM, Nabarra B, et al. Contribution of zinc and other metals to the biological activity of the serum thymic factor. Proceedings of the National Academy of Sciences 1982;79(17):5370-5373. doi.org/10.1073/pnas.79.17.5370
- PubChem, National Library of Medicine. Thymulin, CID 71300623, C33H54N12O15, 858.9 g/mol. Read 2 October 2026. pubchem.ncbi.nlm.nih.gov/compound/71300623
- Anisimov VN, Khavinson VK. Peptide bioregulation of aging: results and prospects. Biogerontology 2010;11(2):139-149. doi.org/10.1007/s10522-009-9249-8
- Bioviridian Inc. Certificate of analysis COA3390, lot THYM20-0318, issued 3 April 2026. Verification code on the certificate. bioviridians.com/coa-search.html
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.
