Semax is a synthetic heptapeptide, Met-Glu-His-Phe-Pro-Gly-Pro, built from the ACTH(4-7) fragment with the tripeptide Pro-Gly-Pro added at the C-terminus. It is a melanocortin-derived sequence that lacks the full melanocortin receptor pharmacophore, and it is used in neuronal and glial cell culture as a tool compound in studies of BDNF and TrkB expression and of neurotrophin-linked signalling. NuVion supplies Semax as a laboratory chemical for in vitro research use only.
Key facts
| Type | Synthetic peptide, ACTH(4-7) analogue with a C-terminal Pro-Gly-Pro extension |
| Amino acid count | 7 |
| Sequence | H-Met-Glu-His-Phe-Pro-Gly-Pro-OH (MEHFPGP) |
| Molecular formula | C37H51N9O10S |
| Molecular weight | Approximately 813.9 g/mol |
| CAS number | 80714-61-0 |
| Synonyms | ACTH(4-7)PGP, Met-Glu-His-Phe-Pro-Gly-Pro |
| Supplied form | Lyophilised powder in a sealed vial |
Structure and chemistry
Adrenocorticotropic hormone is a 39-residue peptide cut from proopiomelanocortin. Residues 4 to 10, Met-Glu-His-Phe-Arg-Trp-Gly, were the starting point for a family of short analogues, and Semax keeps only residues 4 to 7 of that stretch. The His-Phe-Arg-Trp motif at ACTH positions 6 to 9 is the minimal pharmacophore for melanocortin receptor binding. Semax contains the His-Phe half and not the Arg-Trp half, so it does not act as a conventional melanocortin receptor agonist and has no corticotropic activity in steroidogenesis assays on adrenocortical cells. That separation is the point of the design: it retains a melanocortin-derived N-terminal sequence without the receptor activity of the parent hormone.
The Pro-Gly-Pro extension is a glyproline, a motif found in collagen degradation products. Proline residues flanking the C-terminus block most carboxypeptidases and many endopeptidases, so the heptapeptide survives longer in serum-containing medium and in tissue homogenate assays than the unextended ACTH(4-7) tetrapeptide. Cleavage that does occur tends to trim from the N-terminus, giving des-Met Semax (Glu-His-Phe-Pro-Gly-Pro) and shorter fragments, with Pro-Gly-Pro itself released as a stable end product. When peptide identity matters in a time-course experiment, these fragments are the species to look for by LC-MS.
Two side chains govern the chemistry in the vial and in solution. The methionine at position 1 is readily oxidised to the sulfoxide, which adds 16 Da and shows as a shoulder or an earlier-eluting peak on a reversed-phase gradient, so oxidising conditions and prolonged exposure to air in solution are worth avoiding. The histidine at position 3 sits behind a free alpha-amino group, the Xaa-Yaa-His arrangement known as an ATCUN motif, which chelates Cu(II) in a square-planar complex through the N-terminal amine, two backbone amide nitrogens and the imidazole. Semax-copper complexes have been characterised spectroscopically, and the motif also means copper contamination in buffers can change what is measured. The phenylalanine at position 4 gives weak absorbance near 258 nm, though quantification is normally done at 214 nm.
Mechanism of action
The mechanism described most consistently in cell models runs through the neurotrophin system. Exposure of neuronal and glial cultures to Semax raises transcript levels for brain-derived neurotrophic factor (BDNF) and for its receptor TrkB, measured by qPCR, with matching changes in protein by Western blot or ELISA on culture supernatant. BDNF binding dimerises TrkB and triggers autophosphorylation of tyrosines in its cytoplasmic domain, which creates docking sites for Shc and PLCγ. From there the pathway splits three ways: Ras to Raf to MEK to ERK1/2, PI3K to Akt, and PLCγ to diacylglycerol and inositol trisphosphate. ERK and Akt signalling converges on the transcription factor CREB, and because the BDNF gene is itself CREB-responsive, the arrangement forms a positive feedback loop that is often the readout of interest in these experiments.
Transcriptomic profiling of neuronal and glial cultures gives a wider view. RNA sequencing after exposure shows coordinate changes in genes for neurotrophins and their receptors, for neurotransmitter synthesis and transport, and for transcription factors of the immediate early group such as c-Fos and members of the JNK-linked cascade. Protein-level work in the same systems tracks phosphorylated JNK and CREB. These are transcriptional and phosphorylation readouts in cultured cells, and they describe the state of the pathway itself.
The receptor through which Semax initiates this is not established. It has no useful affinity for MC1R to MC5R in binding assays, and it does not raise cAMP in melanocortin receptor reporter lines the way alpha-MSH does, so the melanocortin receptors are ruled out as the route. Candidate explanations under study include action on a distinct surface site, effects of the released Pro-Gly-Pro fragment, and metal-dependent chemistry through the ATCUN motif. In practice the peptide is used as an empirical tool for moving neurotrophin gene expression in culture while that question stays open.
Research applications
Semax sits in NuVion’s Neuroscience category. Typical study contexts include:
- BDNF and NTRK2 transcript measurement by qPCR in primary cortical or hippocampal neuron culture and in glial culture
- TrkB autophosphorylation and downstream ERK1/2, Akt and CREB phosphorylation by Western blot, with TrkB kinase inhibitors as controls
- Neurite outgrowth and differentiation assays in PC12 and SH-SY5Y cells, scored by image analysis
- RNA sequencing and pathway analysis of neuronal and glial cultures, including under low-oxygen culture conditions
- Melanocortin receptor binding and cAMP accumulation assays, where Semax serves as a structurally related inactive comparator to alpha-MSH
- Peptidase stability work comparing ACTH(4-7) with the Pro-Gly-Pro-extended sequence, and copper binding studies of the ATCUN motif by UV-visible, CD and EPR spectroscopy
Handling in the laboratory
Semax is supplied as a lyophilised powder in a sealed vial. Reconstitute with bacteriostatic water run down the wall of the vial; the volume for a given working concentration can be calculated with the reconstitution calculator. The peptide is charged and hydrophilic and dissolves without organic solvent. Keep the sealed vial dry and away from light, refrigerated as stated in the product documentation. Refrigerate the reconstituted solution and use it within the period on the documentation, and split it into single-use aliquots so the stock is not put through repeated freeze-thaw. Because the methionine oxidises, prepare working dilutions close to the time of use, keep headspace air contact short, and use metal-free or chelator-containing buffers if trace copper would interfere. The compound is characterised by RP-HPLC for purity and by mass spectrometry for identity.
Testing and supply from NuVion
NuVion’s Semax comes from GMP-audited manufacture and is independently tested by Janoshik Analytical. Most batches are tested, and the Certificate of Analysis for a tested batch, reporting RP-HPLC purity and mass spectrometry identity, is published on the Semax product page and in the certificates of analysis library. It is supplied lyophilised in sealed vials and dispatched from within Australia.
Related compounds
The nearest sibling in the same category is Selank, a tuftsin-analogue heptapeptide that also carries a C-terminal Pro-Gly-Pro extension and is studied in GABAergic and enkephalin-degradation assays. Pinealon, the tripeptide Glu-Asp-Arg, is used in gene expression work in neuronal cell models.
Frequently asked questions
What is Semax used for in research?
It is used in neuronal and glial cell culture to study BDNF and TrkB expression and the ERK, Akt and CREB signalling downstream of TrkB. It also appears in transcriptomic profiling of neuronal cultures, in neurite outgrowth assays, and as a melanocortin-derived comparator peptide in receptor binding and cAMP assays.
What does the Pro-Gly-Pro extension do?
It is a proline-rich C-terminal cap that blocks carboxypeptidase attack and slows enzymatic breakdown of the peptide in serum-containing medium and tissue homogenates. Comparing Semax with plain ACTH(4-7) in a stability assay is a standard way to demonstrate the difference.
Is Semax a therapeutic good in Australia?
No. NuVion supplies Semax as a laboratory chemical for in vitro research, and it is not for human or veterinary use. The regulatory position is stated in the research use only notice at the end of this article.
How should Semax be stored?
Keep the sealed vial of lyophilised powder dry, away from light and refrigerated as stated in the product documentation. After reconstitution with bacteriostatic water, refrigerate the solution and use it within the period on the documentation. Aliquot the solution for single use, since the methionine residue makes repeated handling in solution a source of oxidised peptide.
Research use only. This product is a laboratory chemical supplied for in vitro research. It is not included in the Australian Register of Therapeutic Goods and has not been assessed by the Therapeutic Goods Administration for quality, safety or efficacy. It is not for human or veterinary use, and nothing on this page is a representation about therapeutic use.
