Hub · Peptide Quality & Verification
Selank vs Semax: are they the same peptide?
Selank and Semax are different peptides (short chains of amino acids, the building blocks of proteins) sharing one ending: both have seven amino acids and end in proline-glycine-proline (Pro-Gly-Pro), per PubChem, a public chemistry database (records 11765600 and 9811102). Selank's first four come from tuftsin, a fragment of an antibody (an immune-system protein), and Semax's first four from adrenocorticotropic hormone (ACTH), a chemical messenger (Volkova et al., 2016; Stavchansky et al., 2022).
01Same peptide?Contents
Your body links amino acids into chains in a set order, and a change in that order makes a different chain. Selank and Semax look alike because two short chains end the same way. This page, part of the peptide quality and verification hub, checks that resemblance against published papers and PubChem.
A match at one end tells you something real, and no more. The table below reads both chains position by position, one amino acid at each. Comparing the studies comes last, because each paper asks its own question.
Key facts
| Selank sequence | Threonine-Lysine-Proline-Arginine-Proline-Glycine-Proline (three-letter codes Thr-Lys-Pro-Arg-Pro-Gly-Pro; one-letter code TKPRPGP) — PubChem |
|---|---|
| Semax sequence | Methionine-Glutamic acid-Histidine-Phenylalanine-Proline-Glycine-Proline (Met-Glu-His-Phe-Pro-Gly-Pro; MEHFPGP) — PubChem |
| PubChem record numbers | Selank 11765600; Semax 9811102 |
| Shared ending | Pro-Gly-Pro, positions 5 to 7 — PubChem |
| Selank formula | C33H57N11O9 (a count of each kind of atom in one molecule: 33 carbon, 57 hydrogen, 11 nitrogen, 9 oxygen) — PubChem |
| Semax formula | C37H51N9O10S (37 carbon, 51 hydrogen, 9 nitrogen, 10 oxygen, 1 sulfur) — PubChem |
| Selank CAS number | 129954-34-3 (Chemical Abstracts Service registry number) — PubChem |
| Semax CAS number | 80714-61-0 — PubChem |
| First four amino acids from | Selank: tuftsin (Thr-Lys-Pro-Arg; Volkova et al., 2016); Semax: ACTH(4–7), amino acids 4 to 7 of ACTH (Stavchansky et al., 2022) |
Are Selank and Semax the same peptide?
Selank and Semax are not the same peptide. The two chains match at three of seven positions and differ at four (PubChem compound records 11765600 and 9811102). Selank starts with threonine, lysine, proline and arginine, and Semax starts with methionine, glutamic acid, histidine and phenylalanine. Their molecular formulas differ as well. A molecular formula counts each kind of atom in one molecule, with C for carbon, H for hydrogen, N for nitrogen, O for oxygen and S for sulfur. Selank is C33H57N11O9, and Semax is C37H51N9O10S, the only one of the pair with a sulfur atom (PubChem).
A certificate of analysis (the supplier's per-batch test sheet) is explained in how to read a certificate of analysis. Form Laboratories lists both names in its research catalogue, for example Semax reference material.
Where do the two sequences come from?
Selank is built on tuftsin and Semax is built on ACTH, and each carries the same Pro-Gly-Pro ending. Tuftsin is a fragment of four amino acids, threonine-lysine-proline-arginine (Thr-Lys-Pro-Arg), from the heavy chain, the larger protein chain, of immunoglobulin G, an antibody type (Volkova et al., 2016). Selank is a synthetic analogue, a lab-made relative of that natural molecule, with Pro-Gly-Pro added at the finishing end of the chain, the C-terminus (Volkova et al., Frontiers in Pharmacology, 2016). Semax joins ACTH(4–7), meaning amino acids 4 to 7 of the ACTH chain, to the same C-terminal Pro-Gly-Pro (Stavchansky et al., Genes, 2022).
Selank was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences (Volkova et al., 2016). Each peptide also has its own starting-reference page: the Selank research guide and the Semax research guide.
What does the shared Pro-Gly-Pro tail do?
Papers describe the Pro-Gly-Pro (PGP) tail as a stability feature. A 2016 paper reports that PGP was added to Selank to improve metabolic stability, meaning resistance to breakdown by the body's enzymes (proteins that cut other molecules) (Volkova et al., 2016). A 2022 paper calls PGP an active factor of resistance to the biodegradation (breakdown in living systems) of peptide drugs (Stavchansky et al., Genes, 2022). In that rat study, PGP alone showed effects unlike Semax's, mostly leaving unchanged the gene activity (how strongly genes are switched on) measured after an induced stroke, a brain blood vessel blocked for a short time on purpose (Stavchansky et al., 2022).
The same study also tested Pro-Gly-Pro-Leu, a four-amino-acid relative of the tail that adds leucine (Leu), and again saw effects unlike Semax's (Stavchansky et al., 2022).
Evidence limits
Can research on Selank and Semax be compared directly?
Research on Selank and Semax cannot be compared directly from the studies cited here, because each asks a different question in a different system. A 2022 study measured gene activity in rat brain after an induced stroke in animals given Semax (Stavchansky et al., Genes, 2022). A 2016 study measured gene activity in the frontal cortex, the front part of the brain, of rats given Selank (Volkova et al., 2016). A 2018 laboratory study examined Selank's molecular effects on GABA receptors, the docking sites for GABA, a chemical messenger that dampens nerve-cell activity (Vyunova et al., Protein and Peptide Letters, 2018). No study cited here tests both peptides together.
Animal and laboratory results do not show effects in people. On scheduling, a search of the Poisons Standard (Australia's national list sorting medicines and poisons into schedules, tiers of control), October 2026 instrument F2026L01327 (the official document holding the lists, in the Federal Register of Legislation), checked 1 October 2026 UTC (world standard time), found no individual entry for Semax or Selank. An absent entry is not permission, and the search draws no conclusion on class membership, a named group of related substances. The research material is not a medicine and is not for human use.
Comparison
Counted from the start of the chain (the N-terminus), with amino-acid codes from the 1984 international naming recommendations (IUPAC-IUB). Sequences and formulas come from PubChem; origins come from Volkova et al., 2016 and Stavchansky et al., 2022.
| Position in the chain | Selank | Semax | Same or different |
|---|---|---|---|
| 1 (start) | Threonine (Thr, T) | Methionine (Met, M) | Different |
| 2 | Lysine (Lys, K) | Glutamic acid (Glu, E) | Different |
| 3 | Proline (Pro, P) | Histidine (His, H) | Different |
| 4 | Arginine (Arg, R) | Phenylalanine (Phe, F) | Different |
| 5 | Proline (Pro, P) | Proline (Pro, P) | Same |
| 6 | Glycine (Gly, G) | Glycine (Gly, G) | Same |
| 7 (end) | Proline (Pro, P) | Proline (Pro, P) | Same |
| Source of positions 1–4 | Tuftsin | ACTH(4–7) | Different |
| Molecular formula | C33H57N11O9 | C37H51N9O10S | Different |
FAQ
Are Selank and Semax the same?
Selank and Semax are two different seven-amino-acid peptides, according to PubChem. They share only their last three amino acids and differ at the first four (PubChem).
Is Selank a version of Semax?
Neither peptide is derived from the other. Selank was designed from tuftsin (Volkova et al., 2016), while Semax was designed from ACTH(4–7) (Stavchansky et al., 2022).
What do the letters in TKPRPGP and MEHFPGP mean?
Each letter is an amino acid's one-letter code: T is threonine, K lysine, P proline, R arginine, M methionine, E glutamic acid, H histidine, F phenylalanine and G glycine (IUPAC-IUB, European Journal of Biochemistry, 1984).
Part of
Peptide Quality & VerificationHow research peptide material is tested, what a certificate of analysis actually records, and how a buyer checks that a vial matches its paperwork. Every article in this hub is about verification, not about use.
Citations
4 sourcesVolkova A et al. Frontiers in Pharmacology. 2016;7:31.
doi:10.3389/fphar.2016.00031Stavchansky VV et al. Genes. 2022;13(12):2380.
doi:10.3390/genes13122380Vyunova TV et al. Protein and Peptide Letters. 2018;25(10):914-923.
doi:10.2174/0929866525666180925144642IUPAC-IUB Joint Commission on Biochemical Nomenclature European Journal of Biochemistry. Nomenclature and symbolism for amino acids and peptides, 1984;138:9-37.
doi:10.1111/j.1432-1033.1984.tb07877.x
Form Laboratories supplies research-use-only reference material. This article is an educational summary of published third-party literature. It is not medical advice, not a use instruction, and research material is not for human or animal use.