Selank vs Semax: Two Heptapeptides With Different Cores

Selank and Semax are both seven-residue synthetic peptides developed in Russia, and both end in Pro-Gly-Pro. Their first four residues come from different natural peptides. Selank is built on tuftsin, Thr-Lys-Pro-Arg, a fragment of immunoglobulin G. Semax is built on Met-Glu-His-Phe, residues 4 to 7 of adrenocorticotropic hormone. They have different sequences, molecular weights of about 751.9 Da and 813.9 Da, and different literatures.

Why do both end in Pro-Gly-Pro?

The Pro-Gly-Pro tail was used as a stabilizing extension. Short natural fragments such as tuftsin and ACTH(4-7) are degraded quickly in biological fluids, and proline-rich sequences resist many peptidases. The degradation of Semax in the presence of rat brain cell cultures has been studied directly [1].

What does each literature cover?

Semax studies, mostly in rodents, examine neurotrophin expression and cholinergic neurons, for example regulation of brain-derived neurotrophic factor and its receptor in the rat hippocampus [2]. Selank studies, also mostly in rodents, examine anxiety-related behavior, memory impairment models and neurotrophic factor content in rats [3]. Both bodies of work come largely from Russian research groups. They are animal and cell findings.

How are they distinguished in the laboratory?

Their masses differ by about 62 Da, and their compositions differ: Semax contains methionine, histidine and phenylalanine, which absorb ultraviolet light and are prone to oxidation at the methionine; Selank contains no aromatic residues and no methionine. Mass spectrometry identifies them unambiguously.

Frequently asked questions

Is there a blend of Selank and Semax?

Some suppliers sell both peptides in one vial. Each component keeps its own identity and should be reported separately on the analytical report.

Are N-acetyl versions the same compounds?

No. N-acetyl and amidated versions of either peptide have different end groups and different masses and should be treated as separate compounds.

Does FLASK list both?

Yes: Selank 10 mg and Semax 10 mg, each with sequence, formula and CAS number on the product page.