Semax and ACTH Fragments: Why ACTH(4–7)-PGP Is a Distinct Peptide Record
Semax is commonly defined in the scientific literature as ACTH(4–7)-PGP: the four-residue ACTH fragment Met-Glu-His-Phe extended by Pro-Gly-Pro. It is not the same peptide as ACTH(4–10), which continues with Arg-Trp-Gly instead of the PGP tail. The shared ACTH-derived prefix does not make the sequences interchangeable.
The distinction should appear in every Semax product record, source table, mass calculation, stability experiment, and literature search. A shorthand reference to “an ACTH fragment” is incomplete unless the residue range and extension are stated.
Write the sequences before comparing evidence
ACTH(4–7) corresponds to Met-Glu-His-Phe. Semax adds Pro-Gly-Pro to that tetrapeptide, producing Met-Glu-His-Phe-Pro-Gly-Pro. ACTH(4–10) instead contains Met-Glu-His-Phe-Arg-Trp-Gly. Both are seven residues long, but residue count is not identity.
Studies indexed by NIH PubMed explicitly describe Semax as ACTH(4–7)PGP or use that identity in transcriptomic experiments. A separate NIH PubMed transcriptome study reports model- and time-specific molecular measurements after ACTH(4–7)PGP exposure. These papers support the named research material and their stated rat models; they do not validate other ACTH fragments or a commercial lot.
The PubChem Semax record provides a chemical-identity reference. Database entries are useful for synonyms and structure checks, but a product or batch still requires its own documentation.
Why the PGP tail matters
Replacing the ACTH(8–10) segment Arg-Trp-Gly with Pro-Gly-Pro changes composition, exact mass, charge distribution, hydrophobicity, protease susceptibility, fragmentation pattern, and potentially the products observed during degradation. It also changes which literature can be matched directly.
The article on Semax parent peptide and fragment profiles explains why detecting an intact signal is different from identifying degradation products. A PGP-containing fragment cannot be assumed to come from ACTH(4–10), and an ACTH(4–10) paper cannot automatically supply a stability profile for Semax.
Evidence map for the two records
| Feature | Semax / ACTH(4–7)-PGP | ACTH(4–10) | Why it matters |
|---|---|---|---|
| Sequence | MEHFPGP | MEHFRWG | Same length, different last three residues |
| Shared region | ACTH residues 4–7 | ACTH residues 4–7 | Supports lineage, not equivalence |
| C-terminal segment | Pro-Gly-Pro | Arg-Trp-Gly | Changes mass, charge, hydrophobicity, and fragments |
| Literature match | Papers that specify ACTH(4–7)PGP or Semax | Papers that specify ACTH(4–10) | Source assignment must follow exact material |
| Analytical confirmation | Intact mass plus sequence-resolved evidence | Intact mass plus sequence-resolved evidence | Nominal residue count is insufficient |
The broader Semax and Selank source-matching guide shows how similar research categories can conceal different sequences. The Semax transcriptome guide focuses on statistics and model limits after the material identity is established.
How to audit a Semax reference
Start with the name used by the paper, then find the exact sequence or supplier description. Check whether the material is Semax, ACTH(4–7), ACTH(4–10), another melanocortin fragment, or a labeled analogue. Record species, tissue, time point, route or exposure method, comparator, and endpoint. If sequence information is absent, mark the identity as uncertain rather than filling it from a neighboring paper.
For the Peptide Bioregulators collection, links should remain material-specific. Semax and Selank can appear in the same research category without sharing sequence, receptor evidence, or degradation products. The COA library should likewise be read by exact product and lot.
Research limitations
ACTH fragment nomenclature varies across older papers, translations, and catalogs. This article uses sequence as the controlling identity. The cited rat-model and molecular studies do not establish human or veterinary use, do not prove equivalence among ACTH fragments, and do not verify a current NEXTWAVE PEPTIDES batch.
Frequently asked questions
Is Semax simply ACTH(4–10)?
No. Both are seven residues long and share ACTH(4–7), but Semax ends in Pro-Gly-Pro while ACTH(4–10) ends in Arg-Trp-Gly.
Does the name ACTH(4–7)-PGP specify the complete sequence?
It specifies the ACTH-derived tetrapeptide plus the PGP extension. A full record should still state terminal groups and the molecular form used.
Can intact mass distinguish the two peptides?
Their compositions and exact masses differ, so accurate intact mass can help. Sequence-resolved fragmentation provides stronger confirmation of the residue order.
Can evidence for ACTH(4–10) be cited as Semax evidence?
Only as background clearly labeled for ACTH(4–10). It should not be presented as direct Semax evidence without an explicit bridge and appropriate limitations.