What Is 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.In vitro · PMID 25310602In vitro · PMID 40496623In vitro · PMID 35080861

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 verified through high-performance liquid chromatography (HPLC), mass spectrometry, and amino acid composition analysis following acid hydrolysis under defined conditions.In vitro · PMID 25310602In vitro · PMID 40496623

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.In vitro · PMID 40496623In vitro · PMID 25310602

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.In vitro · PMID 40496623In vitro · PMID 35080861

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.In vitro · PMID 25310602In vitro · PMID 40496623

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.In vitro · PMID 25310602

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.Review · PMID 28875850Review · PMID 41490200

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.Review · PMID 41004910

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.Review · PMID 42752426In vitro · PMID 40496623

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 verification 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.Review · PMID 42752426

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 verification of the peptide structure. For research applications, this multi-method approach ensures that synthetic semax preparations are chemically defined and suitable for biochemical investigation.Review · PMID 42752426In vitro · PMID 40496623

The studies at a glance

In-vitro biochemical studies examining semax structure, metal coordination, and cellular signaling

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