Semax Peptide: Sequence, ACTH(4-7) Origin, Stability and Analysis

The Semax peptide is a synthetic heptapeptide, Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP), with the formula C37H51N9O10S and a molar mass of about 813.9 g/mol. Its first four residues are the 4-7 fragment of adrenocorticotropic hormone (ACTH), and a C-terminal Pro-Gly-Pro tripeptide takes the place of the Arg-Trp-Gly that follows in the natural sequence. It was developed in the 1980s at the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow, and in rat blood and serum it proved more stable than the natural ACTH(4-10) fragment against most of the enzymes that degrade it [1, 2].

Semax at a glance

Source: PubChem CID 9811102 for formula, mass and CAS; monoisotopic mass calculated from the formula; references 1, 2 and 8.

Research materials: Vortex supplies Semax as a lyophilised research reagent: Semax 10mg. Lab reports: /coa/.

What Semax is: the ACTH(4-7) origin

ACTH is a 39-residue peptide. Its N-terminal region begins Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly, so residues 4 to 10, the fragment called ACTH(4-10), read Met-Glu-His-Phe-Arg-Trp-Gly. The same seven residues also occur in melanocyte-stimulating hormone, which is why older papers write ACTH/MSH(4-10) [2].

Semax keeps only the first four of those residues, Met-Glu-His-Phe, which is ACTH(4-7). The Arg-Trp-Gly that follows in ACTH is replaced by Pro-Gly-Pro. Semax is still widely called “an ACTH(4-10) analogue”, including in paper titles [1, 2], because it was designed as a modified version of that fragment. Strictly, it is ACTH(4-7) joined to Pro-Gly-Pro, and some papers write it that way: ACTH(4-7)PGP.

Semax has no unusual chemistry. All seven residues are standard L-amino acids, both ends are unmodified, and there are no disulfides or cyclisation. Two of the residues are proline, which shapes both its conformation and its resistance to enzymes. How residues are joined and how sequences are written is covered in what are peptides.

Why Pro-Gly-Pro: peptidase stability

Short peptides in serum are cut quickly by peptidases. ACTH(4-10) is no exception. The Pro-Gly-Pro tail was added to slow that breakdown, and the degradation papers measured how far it succeeded and where Semax is still cut.

Where Semax is cut

Potaman and colleagues followed ACTH(4-10) and Semax in rat blood and serum by HPLC [1]. A bestatin-sensitive aminopeptidase accounted for about a third to a half of the serum’s degrading activity. It removed the first and second N-terminal residues, Met and Glu, in turn, giving relatively stable shorter peptides. Against the other enzymes involved, Semax was more stable than ACTH(4-10) [1]. A follow-up inhibitor study in rat serum quantified the contributions [2]. Bestatin inhibited up to 66% of the total degrading activity against both peptides, puromycin about 33% and lisinopril, an angiotensin-converting enzyme inhibitor, about 15%. The authors concluded that aminopeptidases and angiotensin-converting enzyme carry out most of the hydrolysis [2].

Proline explains much of this pattern. Many peptidases cannot cut next to a proline residue, so a C-terminal Pro-Gly-Pro protects that end. The N-terminus stays exposed, so Semax is still trimmed from the front.

Products and pathways with membranes and cultured cells

With plasma membranes prepared from rat basal forebrain, tritium-labelled Semax had a half-life of more than an hour. Dipeptidyl aminopeptidases were identified as the main enzymes, cutting Semax successively to the pentapeptide His-Phe-Pro-Gly-Pro and the tripeptide Pro-Gly-Pro [4]. Zolotarev and colleagues developed an isotope-labelling HPLC method to follow the same process with glial and neuronal cell cultures from the same region [5]. Loss of the N-terminal Met-Glu and of the C-terminal Gly-Pro, giving pentapeptides, was the main process in all the preparations tested, and the product pattern differed between glial and neuronal cultures [5].

Changing the first residue

Because the N-terminus is where aminopeptidases start, Shevchenko and colleagues replaced Met1 with Ala, Gly, Thr or Trp and measured breakdown by an N-aminopeptidase [3]. The Ala, Gly and Thr analogues were more stable than Semax, and their first product was His-Phe-Pro-Gly-Pro. The Trp analogue gave both Glu-His-Phe-Pro-Gly-Pro and His-Phe-Pro-Gly-Pro in similar amounts. All the analogues could act as inhibitors of Semax proteolysis [3].

Source: abstracts of references 1 to 5, checked on PubMed.

Semax variants: N-acetyl Semax and the amidate

Two modified forms circulate under related names. Both are different molecules from Semax, with different formulas and masses, and a lab report has to say which one was tested.

• N-acetyl Semax (Ac-Semax). An acetyl group caps the N-terminal amine. This removes the positive charge at that end and blocks the aminopeptidases that start at a free N-terminus.
• N-acetyl Semax amidate. Acetylated at the N-terminus and amidated at the C-terminus (-CONH2 in place of -COOH), which also removes the negative charge at the C-terminal end.

Source: calculated from the formulas with standard atomic masses. Acetylation adds C2H2O (+42.011 Da); C-terminal amidation replaces OH with NH2 (−0.984 Da).

The acetyl and amidated forms differ by less than 1 Da, about the same as the spacing of the natural ¹³C isotope peaks. A low-resolution spectrum can confuse them, so distinguishing the two needs adequate mass resolution and attention to the isotope pattern. On reversed-phase HPLC, acetylating the N-terminus removes a charged group and changes retention, so the forms usually separate [10].

The acetyl group also changes how the peptide holds metal ions. Magrì and colleagues compared copper(II) and zinc(II) binding by Semax and Ac-Semax [8]. Cu(II)-Semax has a CuN4 chromophore, with the free N-terminal amine as an anchor. With that amine capped, the main Ac-Semax complex at neutral pH was a distorted CuN3O species with a weak axial interaction from the methionine sulfur, and its formal redox potential was more positive. The Semax copper complex was redox-stable and did not react with ascorbic acid, unlike the acetylated form’s complex. Both peptides formed zinc(II) complexes of comparable strength [8]. Copper-peptide coordination in general is covered in our copper peptides explainer.

What the Semax literature looks like

A PubMed search on 21 October 2026 returned 209 records that mention Semax in the title or abstract, 133 of them with Semax in the title. Most come from a small number of Moscow groups, and many are in Russian-language journals or their English translations. The record falls into five broad groups: degradation and peptidase chemistry, binding to membrane preparations, gene-expression measurements in cultured cells and tissue samples, metal coordination chemistry, and rodent pharmacology. This article does not summarise the rodent pharmacology. Its scope is identity, chemistry, and molecule- and cell-level measurements.

What cell and molecular studies of Semax have measured

Each finding below is stated in the model the authors used. These are measurements in cell-free systems, cell cultures or tissue preparations. They do not describe outcomes in an organism.

Specific binding to membrane preparations

Dolotov and colleagues incubated tritium-labelled Semax with plasma membranes from rat basal forebrain [4]. Binding was time-dependent, specific and reversible, and it depended on calcium ions. They reported a dissociation constant of 2.41 ± 1.02 nM and a binding-site concentration of 33.5 ± 7.9 fmol per mg of protein [4].

Neurotrophin mRNA in cultured glial cells

Shadrina and colleagues measured nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNA in glial cells cultured from the basal forebrain of newborn rats after Semax was added [6]. Both mRNAs changed, with the largest change at 30 minutes: BDNF mRNA was eight times the control level and NGF mRNA five times [6].

Inhibition of serum peptidases

Kost and colleagues tested Semax and Selank, a related heptapeptide (Thr-Lys-Pro-Arg-Pro-Gly-Pro) that ends in the same Pro-Gly-Pro, against enkephalin-degrading enzymes in human serum [7]. Semax inhibited them with an IC50 of 10 µM and Selank with an IC50 of 20 µM, compared with 10 mM for puromycin. The pentapeptide fragments of both also inhibited the enzymes, while the tri-, tetra- and hexapeptide fragments did not [7].

Source: abstracts of references 4, 6, 7 and 8, checked on PubMed.

Analytical verification of Semax

Identity by mass spectrometry

Electrospray ionisation brings peptides into the gas phase intact, usually carrying more than one proton [9]. Semax has a basic N-terminal amine and a histidine, so in acidic LC-MS conditions it appears mainly as [M+H]⁺ at m/z 814.36 and [M+2H]²⁺ at m/z 407.68. Tandem MS breaks the backbone into b and y fragment ions. Cleavage on the N-terminal side of proline is typically enhanced, so fragments ending in Pro-Gly-Pro and starting at Pro5 are prominent and confirm the C-terminal tail.

Purity by HPLC

Reversed-phase HPLC with UV detection separates Semax from synthesis-related impurities such as deletion sequences, and from variants. Column chemistry, organic solvent and N-terminal acetylation all shift peptide retention and selectivity [10]. Purity is reported as the main peak’s share of total peak area. It is a relative figure and does not measure water or counter-ions. Our explainer on HPLC peptide purity covers how the number is produced.

The oxidation signature

Methionine is among the residues most prone to oxidation, together with cysteine, histidine, tryptophan and tyrosine, and transition-metal ions and light both promote it [11]. Semax has a methionine at position 1 and a histidine at position 3. Oxidising the methionine to its sulfoxide adds 16 Da (an [M+H]⁺ near m/z 830.35), and the more polar sulfoxide usually elutes earlier on reversed-phase HPLC. A small early peak with that mass is the first thing to look for in an aged sample.

Stability chemistry of lyophilised Semax

The main solid-state reactions of peptides are deamidation, peptide-bond cleavage, oxidation, the Maillard reaction, beta-elimination and aggregation, with temperature, moisture and the physical state of the solid as the main drivers [12]. Semax has no asparagine or glutamine, so deamidation is not a concern. Its methionine is the most oxidation-prone site, and its free N-terminal amine can take part in Maillard chemistry if reducing sugars are present. Cold, dry storage away from light limits both. The background is in storing lyophilised peptides.

Checking a lot of Semax

The Semax 10 mg report on the Vortex COA page covers batch PS07-SX10. It was issued by ILS Laboratories to a wholesale partner facility for that batch and tested on 08/11/2026; the page labels it as a partner-facility report. It lists:

• Purity (HPLC): 99.18%
• Identity (HPLC): confirmed
• Net content: 10.57 mg in a vial labelled 10 mg
• Also listed: heavy metals (ICP-MS), sterility (PCR), endotoxin (USP <85>) and a contaminant screen

Identity on this report is by HPLC, which means the sample’s retention time matched a reference standard. That is a different test from LC-MS, which measures mass directly and is the method that separates Semax from its acetylated and amidated variants. The report carries a COA number and an access code for the lab’s verification portal, linked from the /coa/ page. For a field-by-field walk-through, see how to read a peptide COA.

Frequently asked questions

What is Semax?

Semax is a synthetic heptapeptide, Met-Glu-His-Phe-Pro-Gly-Pro, with a molar mass of about 813.9 g/mol (C37H51N9O10S, CAS 80714-61-0). It joins the ACTH(4-7) fragment to a Pro-Gly-Pro tail. It was developed in the 1980s at the Institute of Molecular Genetics in Moscow.

Why does Semax end in Pro-Gly-Pro?

The Pro-Gly-Pro tail replaces the Arg-Trp-Gly of ACTH(4-10) to slow enzymatic breakdown, since many peptidases cannot cut next to proline. In rat serum, Semax was more stable than ACTH(4-10) against most degrading enzymes, although aminopeptidases still trim it from the N-terminus.

How do N-acetyl Semax and N-acetyl Semax amidate differ from Semax?

N-acetyl Semax carries an acetyl group on the N-terminal amine (C39H53N9O11S, about 856.0 g/mol). The amidate is also amidated at the C-terminus (C39H54N10O10S, about 855.0 g/mol). They are different molecules from Semax, and acetylation also changes how the peptide binds copper(II).

How is the identity of Semax confirmed?

LC-MS confirms identity by mass: Semax gives [M+H]⁺ at m/z 814.36 and [M+2H]²⁺ at m/z 407.68, and tandem MS confirms the sequence. HPLC identity compares retention time with a reference standard. Only a mass measurement separates Semax from its acetylated and amidated variants directly.

About this article: Written by the Vortex Research Editorial Team. Sources are peer-reviewed papers indexed in PubMed, chosen for degradation chemistry, binding, coordination chemistry and cell-level measurements. Each PMID was checked against PubMed for title, journal and year, and each sentence citing a paper was matched to its abstract. Identity data come from the PubChem record, quoted without linking. Variant masses were calculated from their formulas. Publication counts come from a PubMed search run on 21 October 2026.

Research materials: Semax 10mg is supplied as a lyophilised research reagent. Published lab reports are at /coa/.

References

1. Potaman VN, Alfeeva LY, Kamensky AA, Levitzkaya NG, Nezavibatko VN. N-terminal degradation of ACTH(4-10) and its synthetic analog semax by the rat blood enzymes. Biochem Biophys Res Commun. 1991;176(2):741-746. PMID: 1851003. doi:10.1016/s0006-291x(05)80247-5
2. Potaman VN, Alfeeva LY, Kamensky AA, Nezavibatko VN. Degradation of ACTH/MSH(4-10) and its synthetic analog semax by rat serum enzymes: an inhibitor study. Peptides. 1993;14(3):491-495. PMID: 8392718. doi:10.1016/0196-9781(93)90137-6
3. Shevchenko KV, V’iunova TV, Nagaev IIu, Andreeva LA, Alfeeva LIu, Miasoedov NF. [Proteolysis of semax analogues with different N-terminal amino acids by aminopeptidases]. Bioorg Khim. 2011;37(4):475-482. PMID: 22096989. doi:10.1134/s1068162011040133
4. Dolotov OV, Zolotarev IuA, Dorokhova EM, Andreeva LA, Alfeeva LIu, Grivennikov IA, Miasoedov NF. [The binding of Semax, ACTH 4-10 heptapeptide, to plasma membranes of the rat forebrain basal nuclei and its biodegradation]. Bioorg Khim. 2004;30(3):241-246. PMID: 15344653. doi:10.1023/b:rubi.0000030127.46845.f0
5. Zolotarev YA, Dolotov OV, Inozemtseva LS, et al. Degradation of the ACTH(4-10) analog Semax in the presence of rat basal forebrain cell cultures and plasma membranes. Amino Acids. 2006;30(4):403-408. PMID: 16773243. doi:10.1007/s00726-006-0328-8
6. Shadrina MI, Dolotov OV, Grivennikov IA, et al. Rapid induction of neurotrophin mRNAs in rat glial cell cultures by Semax, an adrenocorticotropic hormone analog. Neurosci Lett. 2001;308(2):115-118. PMID: 11457573. doi:10.1016/s0304-3940(01)01994-2
7. Kost NV, Sokolov OIu, Gabaeva MV, et al. [Semax and selank inhibit the enkephalin-degrading enzymes from human serum]. Bioorg Khim. 2001;27(3):180-183. PMID: 11443939. doi:10.1023/a:1011373002885
8. Magrì A, Tabbì G, Giuffrida A, et al. Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties. J Inorg Biochem. 2016;164:59-69. PMID: 27586814. doi:10.1016/j.jinorgbio.2016.08.013
9. Fenn JB, Mann M, Meng CK, Wong SF, Whitehouse CM. Electrospray ionization for mass spectrometry of large biomolecules. Science. 1989;246(4926):64-71. PMID: 2675315. doi:10.1126/science.2675315
10. Mant CT, Cepeniene D, Hodges RS. Reversed-phase HPLC of peptides: assessing column and solvent selectivity on standard, polar-embedded and polar endcapped columns. J Sep Sci. 2010;33(19):3005-3021. PMID: 21038458. doi:10.1002/jssc.201000518
11. Li S, Schöneich C, Borchardt RT. Chemical instability of protein pharmaceuticals: mechanisms of oxidation and strategies for stabilization. Biotechnol Bioeng. 1995;48(5):490-500. PMID: 18623513. doi:10.1002/bit.260480511
12. Lai MC, Topp EM. Solid-state chemical stability of proteins and peptides. J Pharm Sci. 1999;88(5):489-500. PMID: 10229638. doi:10.1021/js980374e

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