Selank and Semax are usually mentioned in the same breath. They are the same length, they come from the same research tradition, they are often supplied in the same formats, and they share a structural trick at the C-terminus. They are also built from completely different parent molecules and are studied along different pathways. This article separates them.
Two sequences, one shared tail
Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues, Thr-Lys-Pro-Arg, are tuftsin, a tetrapeptide described in 1970 as a fragment of the heavy chain of immunoglobulin G with phagocytosis-stimulating activity in vitro. The last three residues, Pro-Gly-Pro, were appended by the synthetic chemists.
Semax is Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues, Met-Glu-His-Phe, are positions four through seven of adrenocorticotropic hormone, the fragment usually written as ACTH(4-7). Semax is therefore described in the literature as an ACTH(4-10) analog in which the C-terminal residues have been replaced by the same Pro-Gly-Pro tail.
That shared tail is the point of the design. Native short peptides are cleared quickly by aminopeptidases and carboxypeptidases. The proline-rich C-terminus resists enzymatic trimming, which extends the measurable half-life of both molecules substantially relative to their parent fragments while leaving the biologically interesting N-terminal tetrapeptide exposed. Two different messages, one delivery chassis.
Where the literature comes from
Both compounds were developed at the Institute of Molecular Genetics in Moscow and characterized largely in Russian-language journals from the late 1980s onward, with a steady flow of English-language publications appearing from the 1990s. This matters when reading the field. The body of work is large but unevenly translated, study designs vary in size and rigor, and independent replication outside that tradition is thinner than for a Western-developed compound of similar age. Claims should be read against that background rather than treated as settled.
Pathways studied for Semax
The most reproduced finding is transcriptional. In rat studies, Semax administration has been associated with increased expression of brain-derived neurotrophic factor and its receptor TrkB in the hippocampus, with changes reported within hours. Related work reports rapid induction of neurotrophin messenger RNA in cultured glial cells. Semax is also studied in rodent models of cerebral ischemia, where the measured endpoints are infarct volume, neurological scoring and gene-expression profiles in the affected tissue rather than anything resembling a clinical outcome.
A second thread concerns the melanocortin family. Because the parent fragment comes from ACTH, the compound has been examined for melanocortin-receptor-linked and neurotrophic effects, notably without the corticotropic activity of the full hormone. The ACTH(4-10) region is the part associated with behavioral and neurotrophic effects in the older peptide literature, and the analog was built to isolate that region.
Pathways studied for Selank
Selank is investigated along two main lines. The first is GABAergic. Rodent transcriptome work reports changes in the expression of genes involved in GABA-A receptor subunit composition and GABA transport in brain tissue after Selank administration, which is the mechanistic story most often offered for its behavior in anxiety models such as elevated plus maze and open field.
The second is enzymatic. Work on human blood plasma reported that Selank inhibits enkephalin-degrading enzymes, slowing the breakdown of endogenous enkephalins. That is an indirect mechanism: the peptide is not proposed to bind an opioid receptor itself, but to change how long the native ligands persist. Tuftsin heritage also keeps immunological endpoints in the picture, with studies examining interleukin expression and immune-cell activity in cell and animal models.
Side by side
| Attribute | Selank | Semax |
|---|---|---|
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Met-Glu-His-Phe-Pro-Gly-Pro |
| Parent molecule | Tuftsin, an IgG heavy-chain fragment | ACTH(4-10), a pituitary hormone fragment |
| Stabilizing motif | C-terminal Pro-Gly-Pro | C-terminal Pro-Gly-Pro |
| Primary pathways studied | GABAergic gene expression, enkephalin degradation, immune signaling | BDNF and TrkB expression, neurotrophic and ischemia models |
| Typical rodent endpoints | Anxiety-model behavior, cytokine profiles | Learning and memory tasks, infarct volume, gene expression |
| Oxidation-sensitive residue | None | N-terminal methionine |
Why they are studied together
The pairing is a design convenience rather than a synergy claim. The two compounds address different systems with the same backbone chemistry, the same solubility behavior and the same handling requirements, so a protocol that covers one covers the other. Laboratories comparing a neurotrophic axis against a GABAergic axis can hold the vehicle, the format and the schedule constant and vary only the peptide. That is why a combined Selank and Semax preparation exists alongside the single-compound vials in the spray formats.
The nasal format in research
Much of the published work on both compounds uses intranasal delivery in animals. The rationale in the literature is the olfactory and trigeminal route, which is studied as a way for a small hydrophilic peptide to reach central tissue without crossing from systemic circulation. That is a research delivery format with its own dosimetry problems, not a convenience feature. Our comparison of intranasal and injectable formats in research covers the trade-offs, and spray preparations use a diluent formulated for that format rather than standard bacteriostatic water.
Handling is otherwise routine. Both arrive as lyophilized powder and follow the same rules set out in our storage and stability guide. The one compound-specific note is Semax and its N-terminal methionine, which is oxidation-prone. Oxidized methionine shows up as a distinct minor peak on the chromatogram, so the certificate is worth reading closely. See how to read a COA.
Frequently asked questions
Are Selank and Semax related molecules?
Only in design. Both are seven residues and both carry the same C-terminal Pro-Gly-Pro stabilizing motif, but their active N-terminal fragments come from unrelated parent proteins and they are studied along different pathways.
Why is so much of the literature in Russian?
Both were developed and characterized in Moscow, and the primary publication record grew up in that language. English-language reviews and primary papers exist and are increasing, but coverage is incomplete and replication outside that tradition remains limited.
Does the Pro-Gly-Pro tail change activity?
It is intended mainly to resist enzymatic degradation and extend measurable half-life. Some reports suggest the tail is not entirely inert and may contribute to observed effects, which is an open question in the literature rather than a settled point.
References
- Najjar and Nishioka, 1970, Nature, Tuftsin: a natural phagocytosis stimulating peptide.
- Dolotov and colleagues, 2006, Brain Research, Semax, an analogue of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus.
- Zozulya and colleagues, 2008, Bulletin of Experimental Biology and Medicine, The inhibitory effect of Selank on enkephalin-degrading enzymes as a possible mechanism of its anxiolytic activity.
- Volkova and colleagues, 2016, Frontiers in Pharmacology, Selank administration affects the expression of some genes involved in GABAergic neurotransmission.
Research use only. This article summarizes published laboratory and preclinical research. Homegrown Peptides products are not for human or animal use, are not drugs, and are not intended to diagnose, treat, cure or prevent any disease. Nothing here is medical advice or a protocol.
