Semax and Selank are often mentioned together, and for a good structural reason. Both are seven-residue synthetic peptides, both were developed at the same Moscow institute, and both end in the same three amino acids. This guide puts their identity data side by side so you can tell them apart at a glance.
Two Different Starting Points
Each peptide begins with a short sequence taken from a larger, naturally occurring molecule.
Semax: built on an ACTH fragment
Semax starts with Met-Glu-His-Phe, part of the adrenocorticotropic hormone (ACTH) fragment 4-10. The published literature describes Semax as an analog of ACTH(4-10).
Selank: built on tuftsin
Selank starts with Thr-Lys-Pro-Arg, the full sequence of tuftsin. Tuftsin is a tetrapeptide that sits inside the Fc region of the heavy chain of immunoglobulin G. It was described by Najjar and Nishioka in 1970.
One Shared Ending: Pro-Gly-Pro
Both peptides finish with the same C-terminal tripeptide, Pro-Gly-Pro (PGP).
| Semax | Selank | |
|---|---|---|
| Origin of first four residues | ACTH(4-7) | Tuftsin |
| Full sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Length | 7 residues | 7 residues |
| CAS number | 80714-61-0 | 129954-34-3 |
| Molecular formula | C37H51N9O10S | C33H57N11O9 |
| Molar mass | 813.9 g/mol | 751.9 g/mol |
Peptides that contain Gly-Pro or Pro-Gly motifs are grouped in the literature as glyprolines. A 2022 paper by Moscow researchers who work on these peptides describes the PGP tripeptide as a factor in a peptide's resistance to biodegradation. In plain terms, the literature links the shared tail to stability, while the first four residues give each peptide its own identity.
Where They Came From
Published work on both peptides lists the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow as the authors' home institute.
What the Published Research Looked At
The literature on these two compounds is mainly preclinical. Examples include:
- Semax: a 2001 study measured neurotrophin gene messages (mRNA) in glial cells cultured from newborn rats. A 2006 study measured related gene and protein markers in rat hippocampus.
- Selank: a 2018 study used radioligand binding assays on brain cell membranes to examine how the peptide interacts with receptor binding sites.
These are cell, tissue and animal experiments. They show what researchers measured under specific laboratory conditions. They are not evidence of any effect in people, and we make no such claims.
Telling Them Apart on the Bench
Because the two names are similar and both end in PGP, mix-ups are easy. A few habits help:
- Check the molar mass on the analytical report: about 813.9 g/mol for Semax versus about 751.9 g/mol for Selank. Mass spectrometry separates them clearly.
- Label aliquots with the full compound name, never an abbreviation.
- Keep the lot number with every aliquot and solution.
See How to Read a Peptide Analytical Report for what each section of the report tells you.
Storage
Both are supplied as lyophilized powders. Store sealed vials cold, dry and away from light, and follow Storing Lyophilized Peptides in the Lab for handling after opening.
FAQ
Are Semax and Selank the same compound? No. They share only the last three residues. Their first four residues, sequences and molar masses differ.
What does Pro-Gly-Pro mean? Proline-Glycine-Proline, the three amino acids at the C-terminal end of both peptides.
What is tuftsin? A four-residue peptide, Thr-Lys-Pro-Arg, found within immunoglobulin G. Selank begins with this sequence.
Sources
- Najjar VA, Nishioka K. Nature, 1970. PubMed 4097539: https://pubmed.ncbi.nlm.nih.gov/4097539/
- Fridkin M, Najjar VA. Critical Reviews in Biochemistry and Molecular Biology, 1989. PubMed 2667894: https://pubmed.ncbi.nlm.nih.gov/2667894/
- Shadrina MI et al. Neuroscience Letters, 2001. PubMed 11457573: https://pubmed.ncbi.nlm.nih.gov/11457573/
- Dolotov OV et al. Brain Research, 2006. PubMed 16996037: https://pubmed.ncbi.nlm.nih.gov/16996037/
- Vyunova TV et al. Protein and Peptide Letters, 2018. PubMed 30255741: https://pubmed.ncbi.nlm.nih.gov/30255741/
- Stavchansky VV et al. Genes (Basel), 2022. PubMed 36553646: https://pubmed.ncbi.nlm.nih.gov/36553646/
- PubChem compound records: https://pubchem.ncbi.nlm.nih.gov/compound/Semax and https://pubchem.ncbi.nlm.nih.gov/compound/Selank
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For in-vitro laboratory research only. Not for human or animal use.
