Semax/Selank Blend

This preparation combines two separately defined synthetic heptapeptides at a fixed ratio. Semax is Met-Glu-His-Phe-Pro-Gly-Pro, built on the ACTH(4-7) tetrapeptide core. Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, built on the tuftsin tetrapeptide core. Being a mixture, it has no CAS number, no molecular formula and no molecular weight of its own.

The two share an unusual amount of design logic. Each is a short bioactive tetrapeptide extended at the C-terminus by the same Pro-Gly-Pro tripeptide, added for the same reason: to resist the exopeptidase activity that would otherwise clear a free tetrapeptide almost immediately. Both emerged from the same research tradition and the same structural strategy.

What they do not share is a target. The parent sequences are unrelated, one derived from a pituitary hormone fragment and the other from an immunoglobulin fragment, and the pathways described for each in the literature do not overlap. A shared stabilising extension is not a shared mechanism.

No primary literature examines this combination as a combination. The available evidence consists of two separate bodies of work on the individual peptides, and any expectation about the mixture is inference across them.

Reported work on Semax centres on neurotrophic gene and protein expression in rodent brain tissue and cultured neurons, including brain-derived neurotrophic factor and its receptor, along with melanocortin-linked signalling inherited from the ACTH-derived core. Reported work on Selank centres on enkephalin-degrading enzyme activity, GABA-A receptor subunit expression, monoamine turnover and cytokine transcript levels. Both literatures are concentrated in a small number of groups and substantially published in Russian-language journals.

The similarity between the two components is an analytical problem rather than a convenience. Both are heptapeptides, their masses differ by roughly sixty daltons, and they share the same C-terminal tripeptide, so their chromatographic behaviour is closer than that of most blend components. Co-elution or partial overlap is a real possibility with a generic gradient.

The shared Pro-Gly-Pro compounds this. Both peptides carry proline isomerism that broadens and splits peaks, so two partially overlapping broadened peaks can integrate into figures that do not represent the true ratio. Ultraviolet peak area alone is not a reliable basis for composition here, and the situation is worse because the two differ in chromophore content, Semax carrying histidine and phenylalanine while Selank carries no aromatic residue at all, so equal masses do not give equal absorbance.

The analysis that actually characterises this material is liquid chromatography with mass spectrometric detection, using extracted ion chromatograms for each component so that identity and quantity are established by mass rather than by retention time and absorbance. Column temperature should be controlled and stated for the same proline-related reason that applies to each peptide individually.