Semax vs Selank: ACTH(4-10) vs Tuftsin Analogue Compared

Semax reproduces a contiguous seven-residue segment of adrenocorticotropic hormone (ACTH), specifically positions 4 through 10, and is frequently catalogued as ACTH(4-7)PGP to reflect the proline-glycine-proline C-terminal motif. Selank, by contrast, is a synthetic analogue of tuftsin (Thr-Lys-Pro-Arg), a tetrapeptide derived from the Fc fragment of immunoglobulin G; the TP-7 construct appends a Pro-Gly-Pro tripeptide to the tuftsin sequence to yield the Thr-Lys-Pro-Arg-Pro-Gly-Pro sequence studied in the cited rat work. The two peptides share no contiguous parent-protein origin and are not fragments of the same larger molecule.

The proline architecture differs in placement. Semax carries a terminal Pro-Gly-Pro triad (positions 5–7), a motif that in the N-acetylated form coordinates Cu(II) and Zn(II) ions in a bidentate fashion documented in a 2016 coordination-chemistry study [4]. Selank distributes its three prolines across positions 3, 5, and 6, interrupting the backbone at two internal points rather than clustering them at the C-terminus. This positional difference alters the conformational envelope each peptide presents to a binding partner, even though the total residue count is identical.

In preclinical models, Semax has been examined within the ACTH/MSH receptor-signalling family. A 2025 study in Bulletin of Experimental Biology and Medicine characterised intracellular calcium dynamics in rat brain neurons following Semax exposure, positioning the peptide as a modulator of Ca²⁺-dependent signalling rather than a direct agonist at a single receptor [1]. Earlier work mapped a protein-expression profile in a rat cerebral ischaemia-reperfusion model [2] and a gene-expression signature spanning immune and vascular pathways in focal ischaemia [3], both consistent with a broad, multi-node effect on neuronal and glial transcriptional programmes.

Selank's preclinical literature clusters around the tuftsin / CCK-B / opioid-interacting axis. A 2022 rat study documented attenuation of morphine-withdrawal behavioural signs [5], and a 2019 hippocampal study linked Selank exposure to BDNF expression changes in the context of ethanol-induced memory impairment [6]. A 2011 Genetika paper examined chemokine, cytokine, and receptor gene expression in response to Selank and its fragments [7], placing the peptide within an immune-modulatory transcriptional context distinct from the calcium-signalling readouts reported for Semax.

The practical distinction for a research protocol is that the two peptides interrogate different downstream cascades: Semax work in the cited literature centres on Ca²⁺ handling and neurovascular gene expression, while Selank work centres on opioid-receptor-interacting behaviour, BDNF-dependent synaptic plasticity, and cytokine/chemokine transcription.

The N-acetylated form of Semax was characterised for its Cu(II) and Zn(II) coordination geometry in a 2016 Journal of Inorganic Biochemistry study [4]. The terminal Pro-Gly-Pro motif provides the bidentate donor set, and the acetylation at the N-terminus removes the free amine that would otherwise compete for the metal centre. No equivalent metal-coordination study has been published for Selank in the cited set, and the interspersed proline positions in Selank do not present the same contiguous bidentate arrangement. This is a structural distinction relevant to any in-vitro assay where trace-metal chelation or metal-dependent enzyme activity is a confound.

A 2006 comparative screen in Izvestiya Akademii Nauk evaluated anticoagulant effects of several proline-containing oligopeptides, including both Semax and Selank, in a preclinical setting [8]. The study is cited here solely as evidence that the two peptides were tested side-by-side in the same assay format; it does not establish a shared mechanism of action. The shared feature is the proline-rich backbone, which constrains conformational entropy and may influence binding kinetics to a range of protein surfaces, but the specific endpoints measured in that screen (clotting-time parameters) are orthogonal to the calcium, BDNF, and cytokine readouts described above.

Both compounds are stocked by HEEZ Research as lyophilized peptides with analytical purity above 99% by HPLC and per-batch COAs published online, intended for laboratory research use. The preclinical literature cited here is exclusively rat-based or in-vitro; no human efficacy, safety, or dosing data are presented or implied.

For a laboratory protocol, the choice between the two depends on the signalling axis under investigation.

Calcium-handling or neurovascular gene-expression assays — for example, ischaemia-reperfusion cell models or Ca²⁺-imaging in primary neurons — align with the Semax literature [1][2][3].

Opioid-withdrawal behavioural paradigms, BDNF-dependent memory tasks, or cytokine/chemokine transcriptional screens align with the Selank literature [5][6][7].

Metal-coordination or inorganic-chemistry characterisation of a proline-rich C-terminal motif is specific to the N-acetylated Semax construct [4].

Comparative anticoagulant screening of proline-oligopeptide backbones can include both [8].

The ACTH(4-10) analogue listing and the tuftsin-analogue listing each carry their own Batch COA and purity specification, so a protocol can reference the exact lot used without cross-contamination of records.

What is the mechanistic difference between Semax and Selank in preclinical models?

Semax is studied as an ACTH(4–10) analogue modulating intracellular calcium dynamics and neurovascular gene expression in rat brain, while Selank is studied as a tuftsin analogue affecting opioid-withdrawal behaviour, BDNF expression, and cytokine transcription in rat hippocampus and peripheral tissue. The two peptides act on non-overlapping signalling cascades in the cited literature.

Do Semax and Selank share a parent protein?

No. Semax derives from a contiguous segment of ACTH (positions 4–10). Selank is a synthetic analogue of tuftsin (Thr-Lys-Pro-Arg), a separate tetrapeptide derived from immunoglobulin G. The two parent sequences are unrelated, and the peptides are not fragments of the same larger molecule.

Are both peptides seven residues long?

Yes. Both are linear heptapeptides with free termini and no lipid modification, cyclisation, or non-proteinogenic residue. The difference lies in proline placement: Semax clusters three prolines at the C-terminus (positions 5–7), while Selank distributes them across positions 3, 5, and 6.

Is there a head-to-head preclinical comparison of the two?

A 2006 comparative screen measured anticoagulant effects of several proline-containing oligopeptides, including both Semax and Selank, in a preclinical assay [8]. No other study in the cited set tests both peptides in the same experimental paradigm.

What purity and documentation does HEEZ Research provide for each?

Both are supplied lyophilized at analytical purity above 99% by HPLC, with per-batch COAs published online and third-party testing. They are intended for laboratory research use only.

Can the two be used in the same in-vitro assay?

The cited literature does not describe a combined-treatment protocol. A researcher designing a comparative assay would need to establish independent dose-response curves for each peptide, given their distinct receptor-class contexts and the absence of a published interaction study.