Selank vs Semax: sequences, parent peptides and identity data

Both peptides attach Pro-Gly-Pro to the C-terminus of a short natural fragment. PGP belongs to the glyproline family of small proline-containing peptides, which a 2002 review in Pathophysiology describes as including PG, GP and PGP and as arising from collagen and elastin turnover and from dietary protein hydrolysates.

Selank starts from tuftsin, the tetrapeptide Thr-Lys-Pro-Arg (PubChem lists tuftsin under CAS 9063-57-4). Research papers on Selank describe it as a synthetic tuftsin analogue; a 2011 study in Regulatory Peptides from the Institute of Molecular Genetics of the Russian Academy of Sciences uses exactly that description.

Semax starts from the ACTH(4-7) fragment, Met-Glu-His-Phe. A 2024 paper in the European Journal of Pharmacology describes Semax as ACTH(4-7)-Pro-Gly-Pro, a noncorticotropic synthetic analog of the ACTH(4-10) fragment.

The two materials differ by about 62 Da (813.9 vs 751.9 g/mol), far more than any normal measurement error, so an LC-MS or MALDI identity result separates them without ambiguity. The observed singly or doubly protonated ion should sit at the value in the table for the compound named on the vial.

HPLC purity cannot distinguish them on its own. A clean single peak says the sample is mostly one substance, not which substance it is. A COA for either peptide should therefore pair the purity result with a mass result.

1. Compound name and labeled quantity match the vial
2. Observed mass matches 752.4 ([M+H]+) for Selank or 814.4 ([M+H]+) for Semax, or the matching doubly charged ion
3. HPLC purity reported with the method and a chromatogram
4. Lot number on the report identical to the lot on the vial

Semax begins with methionine, whose sulfur is easily oxidized to methionine sulfoxide. Oxidation adds 15.995 Da (Unimod accession 35), so an oxidized Semax impurity appears near m/z 830.35 for the singly protonated ion and usually as a separate HPLC peak. Selank has no methionine, cysteine or tryptophan, so this specific impurity does not apply to it.

For any oxidation-prone peptide, lab records should note storage temperature, light protection and how long a stock solution was kept, because those conditions affect what a later re-test will show. Our storage reference covers this for lyophilized material.

This is a structural and analytical comparison for laboratory work. It does not describe effects, uses or administration in people or animals. Catalog materials are sold for qualified in-vitro and analytical research only.