Selank and Semax USA

Selank and Semax share a length, a C-terminal Pro-Gly-Pro tail and a shelf in most catalogues, and that is where the resemblance ends. They come from different parent molecules, differ by 62 Da, and one of them carries a methionine that the other does not. For a laboratory that is the practical difference. This page covers both compounds, the one analytical point that separates them, and ordering within the United States.

Parent molecules

Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro: the tetrapeptide tuftsin, a fragment of immunoglobulin G, extended with Pro-Gly-Pro. Monoisotopic mass is close to 751 Da. It contains no aromatic residue and no methionine.

Semax is Met-Glu-His-Phe-Pro-Gly-Pro: residues 4 to 7 of ACTH extended with the same Pro-Gly-Pro tail. Monoisotopic mass is close to 813 Da. It contains an N-terminal methionine and a phenylalanine.

The Pro-Gly-Pro extension is a stabilising motif that slows removal of residues by exopeptidases, and it is the reason both were designed as they were. Selank and Semax as derivatives of endogenous peptides covers the design logic; Selank, tuftsin and the Pro-Gly-Pro tail and Semax, the ACTH fragment and methionine oxidation take each compound in detail.

The methionine is the difference

Methionine oxidises to the sulfoxide in the presence of dissolved oxygen, adding 16 Da and shifting the peak earlier on a reversed-phase column. In Semax the methionine is at the exposed N-terminus. A fresh Semax certificate shows a main peak at about 813 Da with, at most, a small shoulder at about 829; a report with a large +16 peak is describing material that has aged. Selank has no equivalent concern. In practice, Semax solutions should be made in degassed water or buffer, aliquoted, frozen and used within a short period, while Selank solutions are more forgiving. Both are stable as lyophilised powder at minus 20 °C. Oxidation and other impurities describes the peak pattern.

Detection and quantitation

Neither peptide has a tryptophan or tyrosine, so neither absorbs usefully at 280 nm. Semax’s phenylalanine gives weak absorbance near 257 nm that is not useful for quantitation. Purity has to be measured at 210 to 220 nm, and the certificate should say so. Identity is confirmed by an observed mass within a few daltons of 751 or 813 Da.

Both are small enough that the counter-ion and water are a noticeable share of gross vial mass. Selank, with a lysine and an arginine, carries two counter-ions per molecule in the salt form; Semax carries one on the histidine and has a glutamate that partly offsets it. Where quantitation matters, use the net peptide content figure if reported. Net peptide content explained covers the conversion.

Sizes we supply

• Selank 5 mg and Selank 10 mg.
• Semax 10 mg.

All are lyophilised at 99%+ purity. Published certificates are on the certificates page, and vials are matched to their report by cap and crimp colour.

Ordering in the USA

Orders ship domestically within the United States, so there is no import processing and no customs hold. USPS, UPS and FedEx services are offered at checkout, dispatch is within one business day and typical transit is two to five days. The per-milligram price list shows all three vials on one scale.

Research use only

Selank and Semax from ExoLabz are laboratory reference materials for in vitro and analytical research. They are not drugs and not for human or veterinary use, and we do not provide dosing or administration information. The purity guarantee applies to every vial.