Semax is a synthetic ACTH(4-10) heptapeptide that shows how a short natural fragment can be redesigned for stability in the laboratory. Natural peptide fragments tend to break apart within minutes once enzymes reach them. That fragility is the central chemistry problem this molecule was built to solve.

The answer was a small addition to the end of the chain. Understanding that addition, and the sequence it protects, explains why Semax has become a recurring subject in published peptide research. This article stays on the molecule itself: its structure, the extension that stabilizes it, and what laboratory studies have measured about how it interacts with cells and receptors.

At Janera Science, every compound we supply is defined first by its chemistry. Semax is a clear case study in why sequence design matters, so it is worth examining closely.

What Semax Is: A Heptapeptide Built From an ACTH Fragment

Semax is a synthetic heptapeptide that pairs the core of an adrenocorticotropic hormone fragment with a short stabilizing tail. A heptapeptide is a peptide made of seven amino acids joined by peptide bonds. The molecule was first synthesized in 1982 at the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow (Wikipedia, 2026).

That origin places Semax alongside several other compounds to come out of Russian molecular-genetics research, including Selank. The two share more than a birthplace, as the sections below show.

The parent molecule: ACTH(4-10)

Adrenocorticotropic hormone (ACTH) is a 39-amino-acid signalling peptide. Researchers have long studied short internal segments of it, and the segment spanning residues 4 through 10 is written as ACTH(4-10). Its sequence is Met-Glu-His-Phe-Arg-Trp-Gly.

Semax does not copy that full stretch. It keeps the first four residues, the ACTH(4-7) core (Met-Glu-His-Phe), and then departs from the parent sequence entirely. What replaces the rest is the key to the molecule.

The Semax sequence and molecular identity

The full sequence of Semax is Met-Glu-His-Phe-Pro-Gly-Pro, often abbreviated MEHFPGP. The first four residues come from ACTH; the final three, Pro-Gly-Pro, are a synthetic addition.

The table below lists the molecular identity data that appears on analytical documentation for the compound.

The single sulphur atom in the formula comes from the N-terminal methionine residue. That methionine, together with the histidine two positions along, gives the molecule chemistry that reaches well beyond its length, which is where the research survey later in this article begins.

The Pro-Gly-Pro Extension: Engineering Stability Into a Fragment

The three residues at the end of Semax carry the whole design. Pro-Gly-Pro is a proline-glycine-proline tripeptide added to the C-terminus to slow enzymatic breakdown of the peptide. Removing it returns the molecule to something close to the fragile parent fragment.

Why the native fragment degrades quickly

Small peptides are exposed. Their ends and their internal bonds are open to a wide range of enzymes called peptidases, which cleave peptide bonds and cut the chain into pieces. A free ACTH(4-10) fragment is cleared rapidly once these enzymes act on it.

For a molecule meant to survive long enough to reach and bind a target in a research model, rapid cleavage is the limiting factor. A stabilizing strategy has to protect the vulnerable end of the chain.

How Pro-Gly-Pro resists peptidases

Proline is an unusual amino acid. Its side chain loops back and bonds to its own backbone nitrogen, forming a rigid ring that most peptidases struggle to accommodate. Placing proline at and near the C-terminus creates steric hindrance, a physical crowding that blocks the enzyme from fitting the bond it would otherwise cleave.

The effect is measurable. In a study of Semax binding to rat forebrain plasma membranes, the peptide showed a half-life longer than one hour in the presence of those membranes, and its breakdown produced the smaller fragments HFPGP and PGP through dipeptidylaminopeptidase activity (Bioorganicheskaia Khimiia, 2004). The pattern of fragments confirms that degradation works inward from the chain rather than tearing through the protected proline tail at once.

A shared stabilization strategy with Selank

The same Pro-Gly-Pro tail appears on Selank, the other well-known heptapeptide from the same Russian research programme. Selank places the extension on the tuftsin sequence; Semax places it on the ACTH(4-7) core. The parent sequences differ, yet the stabilization approach is identical.

This is a deliberate molecular-design pattern. Take a short natural sequence with interesting properties, then cap it with Pro-Gly-Pro so it lasts long enough to study. Reading the two molecules side by side makes the strategy easier to recognize.

What the Substitution Changes: Loss of Corticotropic Character

Swapping the C-terminal residues does more than add stability. It also changes what the molecule can no longer do.

The parent hormone ACTH acts strongly at the melanocortin-2 receptor in the adrenal cortex, and the residues Arg-Trp-Gly contribute to that hormonal signalling. Semax removes those residues. The published literature therefore describes Semax as a noncorticotropic analog of ACTH(4-10), meaning the adrenal, hormone-releasing character of the parent is absent from the shortened, Pro-Gly-Pro-capped molecule (Neurochemical Research, 2005).

This is a structural point about sequence and receptor chemistry. The four ACTH-derived residues at the front and the synthetic tail at the back give the molecule a distinct profile from the full hormone. Semax is studied as its own research compound, defined by its own sequence.

Published Laboratory Research on Semax's Molecular Interactions

The literature on Semax spans membrane binding, gene and protein expression, and coordination chemistry. The studies below are laboratory research in cell and animal models, reported here to describe what has been measured at the molecular level. None of it describes use in humans.

Membrane binding and biodegradation

The rat forebrain membrane study cited above measured binding as well as breakdown. Labelled Semax bound the plasma membranes in a time-dependent, specific, and reversible way, with a dissociation constant of about 2.4 nanomolar (Bioorganicheskaia Khimiia, 2004). A dissociation constant in the low nanomolar range indicates a tight, well-defined binding interaction rather than loose association.

Neurotrophic factor signalling: BDNF and TrkB

One line of research has examined how Semax relates to brain-derived neurotrophic factor (BDNF), a protein that supports nerve cell function, and its receptor TrkB. In rat hippocampus, a single administration of Semax was reported to raise BDNF protein levels and increase tyrosine phosphorylation of the TrkB receptor, alongside higher BDNF and trkB messenger RNA (Brain Research, 2006).

Phosphorylation of TrkB is the first step in that receptor's signalling. Measuring it indicates the peptide was linked to activation of the receptor pathway in the tissue studied. The change involved receptor signalling as well as receptor quantity.

Monoaminergic markers

Other rodent-model work has looked at monoamine systems, the neurotransmitter networks built around dopamine and serotonin. Semax was reported to alter dopaminergic and serotoninergic markers in rat brain tissue (Neurochemical Research, 2005). This places the molecule's measured activity across more than one signalling system, which is why the literature describes its profile as multi-target.

Metal-ion coordination chemistry

The histidine and methionine residues make Semax an interesting subject for coordination chemistry, the study of how molecules bind metal ions. Semax binds copper(II) with high affinity and has been reported to protect cultured cells against copper-induced toxicity in laboratory testing (Journal of Inorganic Biochemistry, 2014).

A follow-up study mapped the binding chemistry in detail. The N-terminal amino group and the histidine imidazole act as anchoring points for copper(II) and zinc(II), and acetylating the N-terminus shifted the copper coordination from a four-nitrogen geometry to a three-nitrogen arrangement (Journal of Inorganic Biochemistry, 2016). These results tie the metal-binding behaviour directly to two specific residues in the seven-amino-acid chain.

Handling, Synthesis, and Verification Context

A molecule this defined only stays defined if it is made and checked properly. Semax is produced by solid-phase synthesis, the standard method for assembling peptides one residue at a time on a solid support, then supplied as a lyophilized, or freeze-dried, powder for stability. The lyophilized powder form keeps the peptide dry and shelf-stable until a researcher reconstitutes it.

Confirming that a vial contains the correct seven-residue sequence at high purity requires analytical testing. HPLC and mass spectrometry together verify purity and molecular identity, and the results appear on a lot-specific Certificate of Analysis. You can review those documents on the Janera Science lab results page and learn how to interpret one in our guide to reading a COA.

Every compound described here, Semax included, is supplied strictly for in-vitro laboratory research. Our guide on research use only sets out what that means and who may purchase.

Frequently Asked Questions

What is Semax made of?

Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues come from the ACTH(4-7) core of the adrenocorticotropic hormone fragment ACTH(4-10), and the final three are a synthetic Pro-Gly-Pro tripeptide. Its molecular formula is C37H51N9O10S (PubChem, 2026).

How is Semax different from ACTH(4-10)?

Semax keeps the ACTH(4-7) residues Met-Glu-His-Phe and replaces the Arg-Trp-Gly portion of ACTH(4-10) with Pro-Gly-Pro. That substitution slows enzymatic breakdown and removes the corticotropic character of the parent, so the literature classifies Semax as a noncorticotropic analog (Neurochemical Research, 2005).

Why does Semax contain Pro-Gly-Pro?

The Pro-Gly-Pro tripeptide is added to the C-terminus to resist peptidase enzymes. Proline forms a rigid ring that creates steric hindrance against enzymes that would otherwise cleave the chain, which extends the peptide's measured half-life in laboratory conditions (Bioorganicheskaia Khimiia, 2004).

Is Semax related to Selank?

Both are heptapeptides developed through Russian molecular-genetics research, and both use the same Pro-Gly-Pro C-terminal extension for stability. Their parent sequences differ, since Selank is built on tuftsin and Semax on an ACTH fragment, but the stabilization strategy is shared.

What have laboratory studies measured about Semax?

Published research in cell and animal models has reported specific, reversible binding to brain plasma membranes, changes in BDNF and TrkB expression and receptor phosphorylation in rat hippocampus, effects on dopaminergic and serotoninergic markers, and high-affinity binding to copper(II) and zinc(II) ions (Brain Research, 2006). These are laboratory findings and do not describe use in humans.

How is Semax purity verified?

Purity and identity are confirmed by high-performance liquid chromatography (HPLC) and mass spectrometry, with results recorded on a lot-specific Certificate of Analysis. Each lot supplied by Janera Science is independently tested before release.

Key Takeaways

• Semax is a synthetic ACTH(4-10) heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro, combining the ACTH(4-7) core with a synthetic Pro-Gly-Pro tail (PubChem, 2026).

• The Pro-Gly-Pro extension is the stabilizing feature, using proline's rigid ring to resist peptidases and extend the peptide's measured half-life (Bioorganicheskaia Khimiia, 2004).

• Replacing Arg-Trp-Gly removes the corticotropic character of the parent hormone, so the literature describes Semax as a noncorticotropic analog (Neurochemical Research, 2005).

• Semax and Selank share one stabilization strategy applied to different parent sequences, a pattern that runs through this family of research peptides.

• Published laboratory research spans several molecular systems, including membrane binding, BDNF and TrkB signalling, monoaminergic markers, and copper and zinc coordination (Journal of Inorganic Biochemistry, 2016).

All Janera Science compounds are supplied strictly for in-vitro laboratory research use only. They are not for human or veterinary use and have not been evaluated by the FDA.