Selank is a seven-residue synthetic peptide: tuftsin, the four-residue fragment Thr-Lys-Pro-Arg that occurs naturally in the Fc region of immunoglobulin G, extended with the same Pro-Gly-Pro tail that stabilises Semax. Its mass is 751.9, its CAS number 129954-34-3. It is studied for anxiolytic and neuroimmune signalling, almost entirely in rodent and cell models from Russian laboratories, and the finding most often cited is a change in the expression of GABA-related genes. This post gives the sequence and its origin, what the literature does and does not cover, how Selank differs from the Semax it is so often sold beside, and what the current certificates report for the three formats the catalogue supplies it in: powder, blend with Semax and spray.
What is the sequence, and where does it come from?
| Part | Residues | Origin |
|---|---|---|
| Tuftsin | Thr-Lys-Pro-Arg (TKPR) | Residues 289 to 292 of the IgG heavy chain, released from the Fc region by enzymatic cleavage in the spleen; described in 1970 as a stimulator of phagocytosis |
| Tail | Pro-Gly-Pro (PGP) | Synthetic addition; the same tail used on Semax, chosen because prolines resist peptidase cleavage |
| Selank | Thr-Lys-Pro-Arg-Pro-Gly-Pro | C33H57N11O9, 751.9 |
Tuftsin itself has a half-life of seconds to minutes because peptidases remove it from both ends. The tail was added to protect the C-terminus; the Semax amidate post explains the same design decision for the other peptide that carries it, and the half-life post the general logic. The sequence post covers the one-letter code, TKPRPGP.
At neutral pH Selank carries a free N-terminal amine, a lysine, an arginine and a free C-terminal acid, so it is net positive and very water-soluble. There are no cysteines, no methionine, no tryptophan: none of the residues that oxidise, which makes it one of the more stable short peptides in the catalogue in solution.
What does the literature actually cover?
Three things, and it is worth being exact because "nootropic" is a marketing word, not a mechanism.
GABAergic gene expression. Filatova and colleagues, in IMR-32 neuroblastoma cells, reported that Selank changed the expression of genes involved in GABAergic neurotransmission, and compared the pattern with GABA itself and with olanzapine. This is the cell-level result a laboratory can reproduce, and it is the reason GABA signalling appears on the product page.
Behavioural models. A long series of rodent studies from the Institute of Molecular Genetics and related groups report anxiolytic-type behaviour in standard assays, and Kolik's group reported effects on hippocampal BDNF content in an ethanol-impairment model. These are animal findings, which the trial-data post explains do not transfer to a plate.
Neuroimmune signalling. Tuftsin's original activity is on phagocytes, and Selank inherits an immune literature, mostly cytokine-expression work in rodent models.
What is missing: independent replication outside the originating groups, and any mechanism tied to a defined receptor. The receptor table lists Selank without a single confirmed target, which is the honest entry. A methods section should cite the primary papers and record that.
How does Selank differ from Semax?
They are sold together, they share a tail, and they are different compounds in different systems.
| Selank | Semax | |
|---|---|---|
| Head | Tuftsin, TKPR, from immunoglobulin G | ACTH 4-7, MEHF, from adrenocorticotropic hormone |
| Tail | Pro-Gly-Pro | Pro-Gly-Pro |
| Sequence | TKPRPGP | MEHFPGP |
| Mass | 751.9 | 813.9 |
| Oxidisable residue | None | Methionine at position 1 |
| Charge at pH 7 | Positive (Lys, Arg) | About neutral |
| Literature focus | GABAergic expression, anxiety models, immune signalling | BDNF and trkB expression, neuroprotection models |
| Certificate | COA7627 | COA7586 |
The shared tail is why the two can be co-lyophilized without one degrading the other, which the shared-bottle post works through in detail. It is not evidence they do the same thing.
What do the certificates report?
Three formats, two certificates. All are published unaltered on the certificate page.
| Format | Lot | Certificate | Identity | Content | Purity (RP-HPLC, 214 nm) | Endotoxin |
|---|---|---|---|---|---|---|
| Selank 10 mg powder | SEL10-0803 | COA7627, 17 Aug 2026 | LC-MS/MS, 751.9 | 10.93 mg | 99.83% | < 0.05 EU/mL |
| Selank + Semax 5 mg + 5 mg | SEMSEL5-0803 | COA7604, 17 Aug 2026 | LC-MS/MS, 813.9 and 751.9 | 5.15 and 5.37 mg | 99.76% (one figure for the mixture) | < 0.05 EU/mL |
| Selank spray, 0.5 mg/mL | See product page | None on file |
Two notes. The blend's single purity figure describes the chromatogram of the mixture, not each peptide, which the blend certificate post explains. And the spray has no certificate at present; its page says so, and the powder's certificate does not stand in for it, because a solution at 0.5 mg/mL is a different preparation with its own lot.
How many molecules are in 10 mg?
| Vial | Moles | In 1 mL | In 2 mL |
|---|---|---|---|
| 10 mg | 10 mg ÷ 751.9 g/mol = 13.3 µmol | 13.3 mM | 6.65 mM |
The spray, at 0.5 mg/mL, is 0.665 mM and delivers 50 µg, about 66 nmol, per actuation. The concentration table lists the powder with the other catalogue vials.
How is it handled?
As an easy short peptide. It dissolves immediately in water or reconstitution solution, does not aggregate, and has no oxidisable residue. The free termini are exposed to exopeptidases in serum-containing medium, so its lifetime in a culture well is limited; the tail slows that, it does not stop it. The storage guide windows apply, and the reconstituted-lifetime post puts a peptide like this at the longer end of them.
Frequently asked questions
What is tuftsin?
A natural tetrapeptide, Thr-Lys-Pro-Arg, cut from the Fc region of immunoglobulin G. It was described in 1970 as a stimulator of phagocytosis. Selank is tuftsin with a stabilising tail.
Is Selank a nootropic?
That is the category the catalogue shelves it under, because it is the word buyers use. Its literature is anxiety-model and gene-expression work in animals and cells, from a small number of groups. Cite those papers, not the category.
Is the spray the same as the powder?
Same molecule, different preparation and lot, and no certificate on file for the spray yet. The solution-format post explains why some compounds are offered ready-dissolved.
Why does the blend certificate give one purity figure?
Because purity is read from one chromatogram of the mixture. The two identity masses and two content figures are the component-specific lines; the blend certificate post covers the limit.
What should the methods section record?
"Selank (TKPRPGP, CAS 129954-34-3)", the supplier, lot SEL10-0803, certificate COA7627, the observed mass, and the stock concentration in molar terms. The methods-section post has the template.
References
- Filatova E, Kasian A, Kolomin T, et al. GABA, Selank, and olanzapine affect the expression of genes involved in GABAergic neurotransmission in IMR-32 cells. Frontiers in Pharmacology 2017;8:89. doi.org/10.3389/fphar.2017.00089
- Kolik LG, Nadorova AV, Antipova TA, et al. Selank, peptide analogue of tuftsin, protects against ethanol-induced memory impairment by regulating of BDNF content in the hippocampus and prefrontal cortex in rats. Bulletin of Experimental Biology and Medicine 2019;167(5):641-644. doi.org/10.1007/s10517-019-04588-9
- PubChem, National Library of Medicine. Selank, CID 11765600, C33H57N11O9, 751.9 g/mol, CAS 129954-34-3. Read 28 September 2026. pubchem.ncbi.nlm.nih.gov/compound/11765600
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.
