Selank: Molecular Characterization and Peptide Chemistry — A Research Reference

The sequence is threonine-lysine-proline-arginine-proline-glycine-proline, written TKPRPGP in single-letter code, with a molecular weight of approximately 752 daltons.

The first four residues are tuftsin — threonine-lysine-proline-arginine — a tetrapeptide corresponding to residues 289 through 292 of the heavy chain of immunoglobulin G, released from the parent protein by proteolysis rather than encoded as a standalone gene product. It was identified and named in 1970 [1], and its chemical synthesis and characterization were reported shortly afterward, establishing the sequence independently of the isolation work [2].

The remaining three residues are the appended proline-glycine-proline. Proline is the one amino acid whose side chain closes back onto its own backbone nitrogen, and a proline on the amino side of a peptide bond makes that bond a poor substrate for most peptidases — enzymes that cleave ordinary chains stall at proline. Flanking a glycine with prolines therefore caps the carboxyl end of the molecule against exopeptidase attack while leaving the tetrapeptide of interest chemically untouched. It is the same design logic as the D-amino acid and acyl-group substitutions used elsewhere in this catalogue: modify the site of proteolytic attack, preserve the region of interest.

The composition is strongly basic — a lysine and an arginine both carry positively charged side chains at neutral pH — which accounts for high water solubility. Three of the seven residues are prolines, making this an unusually rigid short chain.

No cell-surface receptor has been established for this peptide, and work on its molecular behaviour has consequently focused on binding interactions and enzymatic breakdown rather than on receptor pharmacology. Studies of the heptapeptide's molecular characteristics have examined its interactions and the fragments generated from it, in a research programme largely published outside the English-language literature [3].

That publication pattern is worth stating plainly, because it affects what a reader can independently verify. Much of the primary work on this compound and its close relatives appeared in Russian-language journals with limited international indexing, so the accessible record is thinner than for compounds of comparable age developed elsewhere. The structural chemistry described above is well established; the mechanistic picture is less so.

The proline-rich composition is itself mechanistically relevant. Proline-containing peptides are substrates for a restricted set of specialized peptidases — prolyl oligopeptidase and dipeptidyl peptidase-4 among them — rather than for general proteases, so the fragment spectrum generated from such a sequence is narrower and more predictable than for an ordinary chain.

Mass spectrometry confirms the intact molecular mass near 752 daltons, distinguishing the full construct from the bare tetrapeptide near 500 daltons by a wide margin, and from an N-acetylated variant by a defined 42-dalton increment.

Reversed-phase HPLC resolves the main peak from related substances and yields the purity figure. A seven-residue synthesis produces few deletion sequences, so the profile is usually simple. The sequence-specific consideration is proline-rich chemistry: sequences containing X-proline motifs are prone during synthesis to diketopiperazine formation, in which two residues cyclize and detach, and proline-containing chains can also present as slowly interconverting conformers, which appear on a chromatogram as broadened or split peaks rather than as genuine impurities. Distinguishing a conformational artefact from a real related substance is a question the chromatogram answers and a headline percentage does not.

One analytical property follows from composition: the sequence contains no aromatic residues and so has essentially no absorbance at 280 nanometres. Detection relies on backbone absorbance near 214 nanometres instead, and any measurement built on 280-nanometre readings is uninformative here.

Net peptide content accounts for counter-ions and residual water, determining how much peptide a nominal milligram figure represents.

Sealed lyophilized material is stable at ambient temperature for the duration of transit and requires no cold chain in shipping. On receipt, vials are refrigerated and kept out of direct light.

Reconstituted material is held refrigerated and used within the window the receiving facility's protocols specify, and repeated freeze-thaw cycling is avoided.

By composition this is one of the more robust entries in the catalogue: no cysteine or methionine removes the common oxidation routes, no asparagine or glutamine removes deamidation, and no tryptophan removes the usual photosensitivity concern. A short, charged, proline-rich chain also dissolves rapidly in aqueous media and presents essentially no surface for aggregation.

The one residue-specific note is the threonine at the amino terminus, whose hydroxyl-bearing side chain makes N-terminal rearrangements possible in solution over extended periods — one more reason solutions are made up as needed rather than held.

Selank is an investigational compound. It has not been approved by the FDA or any other regulatory authority, and no manufacturing, labeling, or quality standards for an approved product apply to it. Research material is sold strictly for laboratory research use; it must not be administered to humans or animals. Researchers are responsible for compliance with all institutional and jurisdictional requirements governing research chemicals.

Each batch of research-grade Selank is accompanied by an independent certificate of analysis specific to that lot.

Selank is a heptapeptide of approximately 752 daltons: the tetrapeptide tuftsin, a fragment of the immunoglobulin G heavy chain identified in 1970 and independently synthesized shortly after, followed by an appended proline-glycine-proline cap that resists exopeptidase attack. No cell-surface receptor has been established for it, and much of its primary literature appeared in journals with limited international indexing. Analytical verification rests on mass discrimination from the bare tetrapeptide and acetylated variants, careful reading of a proline-rich chromatogram where conformers can mimic impurities, detection at 214 rather than 280 nanometres, and batch-specific net peptide content.