Structural and analytical reference
A structural reference for Semax and Selank: seven-residue sequences, parent-fragment relationships, terminal modifications and lot-specific identity checks.
Semax and Selank are different seven-residue peptides. Both end in Pro-Gly-Pro, but their first four residues and parent-fragment relationships differ.
The sequences side by side
| Attribute | Semax | Selank |
|---|---|---|
| One-letter sequence | MEHFPGP | TKPRPGP |
| Three-letter sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Residue count | 7 | 7 |
| Parent-fragment context | ACTH(4–7) joined to Pro-Gly-Pro | Tuftsin-related Thr-Lys-Pro-Arg joined to Pro-Gly-Pro |
| Shared segment | C-terminal Pro-Gly-Pro | C-terminal Pro-Gly-Pro |
Sequences are written from the N-terminus to the C-terminus. The shared ending does not make the complete molecules equivalent. Both the order and identity of all residues matter.
What the names leave unspecified
A basic sequence label does not establish the supplied salt form, counterion content, water content or terminal derivatization. An N-acetyl or amidated derivative is a modified chemical identity and should be named explicitly. Evidence for the unmodified sequence should not be assigned automatically to that derivative.
Semax is commonly described as an ACTH(4–10) analogue, but its sequence is not the native ACTH(4–10) sequence. The more specific ACTH(4–7)-PGP notation makes the design relationship clearer. Selank has a different starting fragment.
A useful molecular-profile review
- Start with the complete seven-residue sequence rather than the shared PGP ending.
- Confirm whether both termini are unmodified or explicitly derivatized.
- Match the expected mass to that chemical identity and the reported mass convention.
- Separate chromatographic area purity from the amount of peptide in the powder.
HPLC retention depends on the analytical method. A retention time from a different column, gradient or instrument is not a standalone identity test. Mass evidence adds another analytical view, but its assignment still needs the correct structural expectation.
Reading a supplier record
A strong comparison uses records from the actual materials being considered. Check the report issuer, tested sample label, lot number and method details. The paper that defines a sequence is an identity reference; it does not certify the supplier batch.
SRL publishes available Semax and Selank sample reports. Compare each report with its own lot label, and confirm current fulfillment information separately. Neither a shared format nor a shared percentage is evidence of chemical interchangeability.
Frequently asked questions
Why do both sequences end in PGP?
The published designs both include the Pro-Gly-Pro segment. Their complete sequences and structural origins still differ.
Does a seven-residue count imply the same molecular mass?
No. Residues have different compositions, and modifications can further change the molecular profile.
Is N-acetyl Semax the same entry as Semax?
An acetyl modification changes the declared structure. Record it explicitly and require corresponding identity evidence.
Continue learning
Compare parent Semax and terminal modifications in Semax vs N-Acetyl Semax Amidate.
Sources and scope
- Semax primary laboratory study (2022). Sequence and ACTH-fragment relationship.
- Selank primary IMR-32 cell study (2017). Sequence and tuftsin-related design; no biological outcome claims are made here.
This original SRL reference uses the linked scientific and labeling records for molecular or analytical context. It does not reproduce an experimental protocol or certify a supplier batch. Prepared October 2, 2026.
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