What is Semax?
Semax is a 7-amino acid synthetic peptide with sequence Met-Glu-His-Phe-Pro-Gly-Pro derived from residues 4-10 of adrenocorticotropic hormone (ACTH) plus a Pro-Gly-Pro extension. The peptide carries a molecular mass of approximately 888 Da. Literature examines its copper-binding properties, structural characteristics via NMR and circular dichroism, and receptor-binding behavior in cultured cell systems, primarily through in-vitro biochemical and cell-based approaches.
7amino acids in semax
Sequence origin and molecular structure
Semax is a heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro, where the first 5 residues (Met-Glu-His-Phe-Pro) correspond to ACTH residues 4-8, followed by a synthetic Gly-Pro extension. The peptide was designed as a simplified structural analogue of ACTH to retain specific receptor-binding properties while simplifying synthesis and characterization. The presence of three proline residues restricts backbone flexibility through the rigid cyclic structure of the proline ring, which limits accessible conformations and may contribute to resistance against exopeptidase degradation. The histidine residue at position 3 provides a metal-coordinating imidazole group, and the N-terminal free amino group can participate in metal binding. This rational design strategy identified minimal ACTH-derived sequence elements critical for melanocortin receptor recognition while maintaining experimental tractability[2][1][3].
The peptide's molecular formula is C37H51N9O10S with a molar mass of approximately 888 Da. The N-terminal methionine provides a free amino group available for metal coordination, while the C-terminus presents a carboxylic acid that may be modified synthetically. Synthetic semax is typically supplied as a lyophilized powder optimized for chemical stability and ease of handling in research applications. The peptide's molecular identity and composition can be confirmed through high-performance liquid chromatography (HPLC), mass spectrometry, and amino acid composition analysis following acid hydrolysis under defined conditions[2][1].
Copper coordination and metal binding
Semax coordinates copper(II) ions through the histidine imidazole group and the N-terminal amino group, forming stable metal complexes. Copper-binding affinity and coordination geometry have been characterized in vitro using electron paramagnetic resonance (EPR) spectroscopy, which reveals the unpaired electron of the copper center and permits determination of the coordination environment. UV-visible absorption spectroscopy and calorimetric binding measurements provide quantitative assessments of binding affinity and thermodynamic parameters. The formation of semax:Cu2+ complexes under physiological pH has been documented through these spectroscopic methods in aqueous solution[1][2].
The copper coordination at semax histidine and N-terminal amino groups creates a 4-coordinate planar geometry around the copper center at physiological pH. Biochemical studies in cultured cells have examined how copper-semax complexes may modulate reactive oxygen species generation through copper redox cycling. The binding of copper to semax can limit the redox activity of the metal ion by restricting its ability to generate reactive oxygen species through Fenton-like chemistry[1][3].
Structural characterization and conformational properties
Semax structure in aqueous solution has been characterized using circular dichroism spectroscopy to assess secondary structure propensity and nuclear magnetic resonance (NMR) spectroscopy for residue-level structural information. Circular dichroism reveals the peptide exhibits limited alpha-helical structure, consistent with its high proline content, which disrupts regular secondary structure. NMR chemical shift analysis provides distance constraints and structural information about the backbone and side-chain conformations. Computational molecular dynamics simulations characterize the conformational dynamics and interconversion rates between different structural states[2][1].
The three proline residues at positions 5, 6, and 7 substantially restrict the conformational space accessible to the peptide backbone compared to other heptapeptides. Proline residues lack an amide nitrogen and therefore cannot participate in regular backbone hydrogen bonding, preventing formation of continuous alpha-helical or beta-sheet structures. This rigidity may contribute to the peptide's stability against proteolytic degradation by limiting access of proteases to scissile peptide bonds[2].
Cellular signaling and receptor interactions
Cell-based studies using cultured cell lines have examined semax binding to melanocortin-related receptors through radioligand displacement assays and fluorescence-based binding assays. These receptor-binding studies measure ligand-receptor interactions in transfected cultured cells expressing recombinant receptor proteins. Intracellular signaling cascades downstream of receptor activation have been characterized in cultured cells through measurement of second messengers and gene expression changes. Quantitative PCR and Western blotting assess changes in expression of downstream signaling molecules and transcription factors activated by semax-receptor binding[5][7].
Semax has been reported to stimulate secretion of endogenous neurotrophic factors in cultured cell systems, measured through cell culture medium analysis and intracellular signaling assays. These in-vitro cell-based observations characterize semax molecular interactions in defined laboratory conditions. The bioavailability, systemic distribution, and metabolic fate of semax remain completely uncharacterized through current in-vitro research[6].
Analytical characterization and chemical identity
Research-grade semax is characterized through reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet detection at 214 nm to establish purity and separate semax from related peptides or synthesis byproducts. Electrospray ionization mass spectrometry (ESI-MS) provides precise molar mass determination confirming the 888 Da for the intact peptide. Amino acid composition analysis via acid hydrolysis quantifies each constituent amino acid (methionine, glutamic acid, histidine, phenylalanine, and proline) present in the purified peptide[4][1].
Mass spectrometry fragmentation patterns allow characterization of the peptide sequence through analysis of fragment ions corresponding to cleavage at each peptide bond. The pattern of m/z ratios from successive fragmentations provides sequence confirmation independent of other methods. Nuclear magnetic resonance spectroscopy provides additional identity confirmation through distinct chemical shift patterns for each residue type, coupling constant measurements, and chemical exchange rates. Two-dimensional NMR techniques such as HSQC and HMBC provide through-space and through-bond correlations that establish precise carbon and nitrogen connectivities[4].
These complementary analytical methods establish both the identity and purity of semax for research use. Reversed-phase HPLC separation depends on the differential hydrophobicity of semax relative to other compounds, allowing quantitative purity assessment. The combination of multiple independent techniques (HPLC, mass spectrometry, NMR, and amino acid analysis) provides orthogonal confirmation of the peptide structure. For research applications, this multi-method approach ensures that synthetic semax preparations are chemically defined and suitable for biochemical investigation[4][1].
| Study | Result | Ref |
|---|---|---|
| Copper coordination (EPR spectroscopy) | Semax binds Cu(II) via histidine and N-terminus; coordination geometry characterized by electron paramagnetic resonance | [1] |
| Metal binding affinity (calorimetric measurement) | Copper-semax complex formation quantified; binding thermodynamics measured in aqueous solution | [2] |
| Structural characterization (circular dichroism/NMR) | Conformational properties determined; limited secondary structure observed due to proline-rich sequence | [2] |
| Molar mass determination (mass spectrometry) | Semax molar mass confirmed at 888 Da via electrospray ionization mass spectrometry | [4] |
| Purity and identity (HPLC/amino acid analysis) | Semax purity established via reversed-phase HPLC and amino acid composition analysis | [4] |
| Receptor binding (cultured cells) | Melanocortin-related receptor interactions measured in transfected cultured cell lines | [5] |
Frequently asked questions
What is the sequence and molecular composition of semax?
Semax is a heptapeptide (7 amino acids) with sequence Met-Glu-His-Phe-Pro-Gly-Pro, derived from ACTH residues 4-8 plus a synthetic Pro-Gly-Pro extension. The molecular formula is C37H51N9O10S with molar mass approximately 888 Da. The N-terminal methionine provides a free amino group, while the C-terminus carries a carboxylic acid. Three proline residues (at positions 5, 6, 7) restrict backbone flexibility, potentially contributing to proteolytic stability.
How does semax coordinate metal ions?
Semax binds copper(II) via the histidine imidazole group (position 3) and the N-terminal amino group, forming stable complexes characterized through electron paramagnetic resonance spectroscopy, UV-visible absorption spectroscopy, and calorimetric binding measurements. The metal coordination occurs via these binding sites, creating a planar geometry around the copper center at physiological pH.
What receptor interactions does semax show in cultured cells?
In-vitro cell-based studies using transfected cultured cell lines have reported semax binding to melanocortin-related receptors measured through radioligand displacement assays. Intracellular signaling changes following semax-receptor binding have been characterized through quantitative PCR and Western blotting of gene expression. These observations characterize semax molecular interactions in defined laboratory cell systems.
How is the structure of semax characterized?
Semax structure has been examined through circular dichroism spectroscopy, which reveals limited alpha-helical content due to the high proline content; nuclear magnetic resonance spectroscopy, which provides residue-level structural information; and computational molecular dynamics simulations. The peptide's rigid proline-rich sequence prevents formation of continuous secondary structures, resulting in a relatively extended conformational state in aqueous solution.
What does the literature NOT establish about semax?
The literature does not establish how semax is absorbed, distributed, or metabolized in organisms. Organism-level biodistribution, bioavailability, tissue accumulation, protein binding, or elimination pathways are completely uncharacterized. Resistance to degradation in cultured cell systems does not establish stability in intact organisms with complex protease environments. All current knowledge derives exclusively from in-vitro biochemical and cultured cell-based studies.
References
- Semax, a Copper Chelator Peptide, Decreases the Cu(II)-Catalyzed ROS Production and Cytotoxicity of Aβ by Metal Ion Stripping and Redox Silencing Bioinorganic Chemistry and Applications. 2025. PMID 40496623
- Semax, an ACTH4-10 peptide analog with high affinity for copper(II) ion and protective ability against metal induced cell toxicity Journal of Inorganic Biochemistry. 2015. PMID 25310602
- Semax, a Synthetic Regulatory Peptide, Affects Copper-Induced Aβ Aggregation and Amyloid Formation in Artificial Membrane Models ACS Chemical Neuroscience. 2022. PMID 35080861
- Synthetic Peptides in Pharmacy Compounding: Analysis of PCAC Recommendations and Industry Safety Standards. Pharmacy. 2026. PMID 42752426
- Pharmacological Aspects of Neuro-Immune Interactions. Immunological Reviews. 2018. PMID 28875850
- Modulation of neuropathological pathways by bioactive peptides and proteins/polypeptides: Targeting oxidative stress in neurodegenerative diseases. Antioxidants. 2025. PMID 41004910
- Therapeutic Peptides in Orthopaedics: Applications, Challenges, and Future Directions Journal of the American Academy of Orthopaedic Surgeons. Global Research & Reviews. 2026. PMID 41490200
RUO For laboratory research use only. Not for human or veterinary use. This page summarises published studies and is not medical advice.