Semax vs Selank: Structure, Identity and Research Models

Semax and Selank are distinct heptapeptides

Semax and Selank are different seven-residue peptides. Semax is MEHFPGP; Selank is TKPRPGP. They share the terminal sequence Pro-Gly-Pro (PGP), but the four residues before it come from different peptide families. That difference changes the complete sequence, elemental formula, molecular mass, and analytical identity.

A technically valid comparison identifies the material used in each paper, the experimental model, the measured endpoint, and the evidence connecting a tested lot to the named compound.

Field Semax Selank
Three-letter sequence Met-Glu-His-Phe-Pro-Gly-Pro Thr-Lys-Pro-Arg-Pro-Gly-Pro
One-letter sequence MEHFPGP TKPRPGP
Residue count 7 7
Molecular formula C37H51N9O10S C33H57N11O9
Average molecular weight 813.9 g/mol 751.9 g/mol
PubChem CID 9811102 11765600
CAS Registry Number 80714-61-0 129954-34-3
Parent-peptide relationship ACTH(4-7) followed by PGP; commonly described as an ACTH(4-10) analogue Complete tuftsin sequence TKPR followed by PGP

These values describe the unmodified neutral sequences in the cited PubChem records. A salt, terminal modification, fragment, or related analogue requires its own identity record.

The shared PGP segment does not make them interchangeable

Semax:  M E H F P G P
Selank: T K P R P G P
                -----
                shared terminal PGP

Semax begins with MEHF, the ACTH(4-7) sequence. Selank begins with TKPR, the complete tuftsin sequence. The shared terminal PGP explains why the compounds are often discussed together, but it does not transfer a result from one complete peptide to the other.

  • Native corticotropin(4-10) is MEHFRWG, not MEHFPGP. Semax is related to that ACTH region but is not the native sequence.
  • Tuftsin is TKPR, not TKPRPGP. Selank contains tuftsin as its first four residues and adds PGP.

A paper about native ACTH, corticotropin(4-10), tuftsin, or a shorter fragment is supporting context, not direct evidence about the full Semax or Selank sequence.

Their research literatures emphasize different models

Semax papers accessible through PubMed include rat cerebral-ischemia models, rat brain-region protein and transcript measurements, and rat brain-slice calcium experiments. Selank papers include mouse-spleen transcription panels, a human neuroblastoma cell-line study, isolated brain-membrane binding, and strain-dependent rodent behavioral designs.

Those categories are not evidence of two settled mechanisms. Transcript abundance, selected protein levels, membrane binding, intracellular calcium, and behavior are different endpoints. A pathway label shared by two papers does not make their experiments equivalent.

The individual Semax identity guide and Selank identity guide map representative studies and their limitations in more detail.

What direct comparison studies actually measured

Only a small subset of papers put both peptides into the same experimental design.

Kost et al., 2001, PMID 11443939

System and comparison
In-vitro assay of enkephalin-degrading enzymes in human serum; Semax and Selank were tested in the same biochemical system
What it can establish
A concentration-dependent difference under that enzyme assay
What it cannot establish
A human clinical effect, a complete mechanism, or equivalence in another assay

Slominsky et al., 2017, PMID 28702721

System and comparison
Behavioral readouts in rats with 6-OHDA-induced parkinsonism; both peptides were included
What it can establish
Model-specific, nonuniform behavioral observations in that rat design
What it cannot establish
A general ranking of the compounds or transfer to people

Panikratova et al., 2020, PMID 32342318

System and comparison
Resting-state fMRI functional-connectivity comparison in 52 healthy participants, including Semax, Selank, and placebo groups
What it can establish
Differences in a narrow imaging endpoint involving predefined brain regions
What it cannot establish
Clinical benefit, cognitive performance, symptom treatment, or long-term outcome

The 2001 paper is a biochemical experiment using human serum, not a trial in people. The 2020 paper involved human participants, but its reported endpoint was short-window resting-state functional connectivity. It did not establish that either compound improves cognition, treats anxiety, or produces a durable outcome.

The rat paper also reported nonuniform endpoints across the two peptides. A direct comparison can remain narrow, model-dependent, and unsuitable for ranking materials outside that design.

Analytical reports must remain compound- and lot-specific

Semax and Selank have different sequences, formulas, and molecular masses. A Semax identity result cannot authenticate Selank, and a Selank report cannot authenticate Semax. Each material requires its own lot-matched record.

  1. Match the material name and physical lot code to the report.
  2. Confirm that the report identifies the tested sample and laboratory.
  3. Read identity, chromatographic purity, and quantitative content as separate fields.
  4. Check the method and report limitations before using a result as an acceptance criterion.

Use BulkGLP’s current and historical batch records to find the applicable report. The peptide COA guide explains what common analytical fields can and cannot show.

How to select a material for a replication study

Start with the source paper. Record the exact sequence or named material, chemical form if stated, comparator, biological model, tissue or cell line, collection window, assay, controls, and statistical plan. Then set lot-specific identity and quantitative acceptance criteria that match the experiment.

If a paper names Semax, substituting Selank changes the experimental material. If it names Selank, substituting Semax does the same. The shared PGP segment is not a basis for interchangeability.

Semax and Selank comparison questions

Are Semax and Selank the same peptide?

No. Semax is MEHFPGP; Selank is TKPRPGP. They share only the terminal PGP segment.

Why are Semax and Selank often grouped together?

Both are synthetic heptapeptides with a terminal PGP sequence and overlapping research history. That shared context is useful for comparison, but it does not make their parent sequences or evidence records equivalent.

Does the shared PGP sequence mean one peptide’s results apply to the other?

No. A result belongs to the complete tested molecule, assay, model, and endpoint. It should not be transferred on the basis of a shared three-residue segment.

Can one analytical report support both compounds?

No. Their complete sequences and expected molecular masses differ. Each compound and lot needs its own traceable analytical record.

Does the comparison establish a desired human effect?

No. It distinguishes molecular identity and experimental evidence. The cited designs do not support a personal-use prediction or effects-based recommendation.

Primary and authoritative sources

  1. NLM PubChem: Semax, CID 9811102
  2. NLM PubChem: Selank, CID 11765600
  3. NLM PubChem: Corticotropin(4-10), CID 123787
  4. NLM PubChem: Tuftsin, CID 156080
  5. Kost et al. (2001), PMID 11443939
  6. Slominsky et al. (2017), PMID 28702721
  7. Panikratova et al. (2020), PMID 32342318
  8. Medvedeva et al. (2014), PMID 24661604
  9. Kolomin et al. (2011), PMID 21609736
  10. Filatova et al. (2017), PMID 28293190

Get 10% Off Your Order!

Join our list and get an instant discount code.

You're In!

Use this code at checkout:

Get 10% Off
Get 10% Off
0