Selank is a synthetic seven-residue peptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro. It joins the tetrapeptide tuftsin (Thr-Lys-Pro-Arg) to a Pro-Gly-Pro extension, a design intended to make a short peptide harder for enzymes to break down. Most of what has been firmly measured about Selank is biochemistry: how it is broken down in plasma and how it affects peptide-degrading enzymes in assays. This article covers its identity, chemistry, the laboratory studies in which it has been examined, and general storage. Selank sold on this site is for laboratory research use only.
What Selank is
Selank is written in one-letter code as TKPRPGP and in three-letter code as Thr-Lys-Pro-Arg-Pro-Gly-Pro (H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH). All seven residues are standard L-amino acids, and the chain is unmodified, with a free N-terminal amine and a free C-terminal carboxylic acid. It falls into two parts:
- Positions 1-4, Thr-Lys-Pro-Arg: the tuftsin sequence. Lysine and arginine carry basic side chains, so the peptide has a net positive charge at neutral pH.
- Positions 5-7, Pro-Gly-Pro: a synthetic C-terminal extension. Proline restricts backbone rotation and is a poor substrate for many peptidases.
Three of the seven residues are proline. The sequence contains no cysteine, methionine or tryptophan, so it has no easily oxidised side chain. With no tryptophan or tyrosine, it absorbs only weakly at 280 nm.
Origin
Tuftsin is a four-residue sequence that occurs within the heavy chain of immunoglobulin G (IgG). It was isolated, and its structure confirmed by chemical synthesis, in the early 1970s (Nishioka et al., 1972; PMID: 4112769). Selank extends that sequence at the C-terminus with Pro-Gly-Pro, a motif from the peptide family known as glyprolines. Papers on the heptapeptide have been indexed since the mid-1990s.
Chemical identity
| Property | Value |
|---|---|
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP) |
| Systematic name | L-threonyl-L-lysyl-L-prolyl-L-arginyl-L-prolylglycyl-L-proline |
| Molecular formula | C33H57N11O9 |
| Average molecular weight | 751.9 g/mol |
| Monoisotopic mass | 751.4341 Da |
| Expected [M+H]+ | m/z 752.441 |
| Expected [M+2H]2+ | m/z 376.724 |
| CAS number | 129954-34-3 |
| PubChem CID | 11765600 |
| Typical form | Lyophilized (freeze-dried) powder |
The formula, masses and CAS number above match PubChem compound record CID 11765600, which describes the neutral free peptide. Calculated from standard atomic weights, the formula gives 751.89 g/mol. Material is often supplied as a salt, commonly an acetate, and a salt form weighs more per mole than the free peptide. Because the molecule carries two basic residues, electrospray mass spectra often show the doubly charged ion near m/z 376.72 alongside the singly charged ion near m/z 752.44.
Stability and degradation in plasma
Zolotarev et al., 2006 (Bioorg Khim; PMID: 16637290) prepared Selank labelled with tritium across all of its residues, by high-temperature solid-phase catalytic isotope exchange, at a specific radioactivity of 50-150 Ci/mmol. Because every residue carried label, the authors could follow each fragment produced as the peptide was hydrolysed. In blood plasma, the major degradation products they identified were the pentapeptide TKPRP, the tripeptide TKP and the dipeptides RP and GP.
Taken together, these products are consistent with cleavage of the Pro5-Gly6 and Pro3-Arg4 bonds. For analytical work they are useful reference points: a stability-indicating HPLC method can be checked for its ability to separate the intact heptapeptide from these shorter fragments.
Enzyme-inhibition assays
Two studies measured Selank as an inhibitor of the blood enzymes that hydrolyse enkephalins, a group of naturally occurring pentapeptides. These enzymes are often called enkephalinases.
- Kost et al., 2001 (Bioorg Khim; PMID: 11443939) measured hydrolysis of enkephalin by human serum enzymes in the presence of Selank and of the related heptapeptide Semax. Selank inhibited the reaction in a concentration-dependent way, with an IC50 (the concentration giving half-maximal inhibition) of about 20 micromolar. That was more potent than puromycin (IC50 about 10 millimolar) and bacitracin. Pentapeptide fragments also showed inhibition, while tri-, tetra- and hexapeptide fragments did not.
- Zolotarev et al., 2004 (Bioorg Khim; PMID: 15344652) developed an assay using Leu-enkephalin labelled with tritium at all residues (120 Ci/mmol), with the radioactive fragments separated by HPLC. In plasma, aminopeptidases, dipeptidylaminopeptidases and dipeptidylcarboxypeptidases accounted for about 80%, 2% and 10% of enkephalin-degrading activity. Bestatin mainly inhibited aminopeptidases and carboxypeptidases, while Selank was more specific for carboxypeptidase and dicarboxypeptidase activity.
These are measurements in plasma and serum. None of them establishes any use in people, and the material described here is not intended for one.
Related: see our Selank compound page for the catalogue summary.
Storage and handling of lyophilized peptides
Selank, like most research peptides, is supplied as a lyophilized powder. General laboratory practice for this kind of material:
- Long-term storage: keep sealed vials frozen, commonly at -20 C, away from light.
- Moisture: let a cold vial reach room temperature before opening it so condensation does not form inside, and reseal it promptly.
- Temperature cycling: repeated freezer cycling can speed up degradation, so many labs aliquot material at the outset.
- Records: log the receipt date, storage location and lot reference so results can be traced to a specific batch.
A few points are specific to this sequence. With no cysteine, methionine or tryptophan, oxidation is a minor concern compared with hydrolysis and moisture uptake. The plasma data above show that blood enzymes cleave the chain readily, so biological matrices are a source of degradation in any experiment that uses them. Because the peptide lacks aromatic residues, HPLC detection is usually done at low UV wavelengths, around 210-220 nm, where the peptide bond absorbs.
For the 10mg strength, the certificate published under laboratory ID V260213-13-003, for lot S26C800, reports a chromatographic purity result by HPLC-UV/VIS; the measured figure is printed on the certificate itself and applies only to that tested lot. Published reports are listed on the Certificates page.
Product details for the material sold on this site are on the Selank product page.
FAQ
What is Selank?
Selank is the synthetic heptapeptide Thr-Lys-Pro-Arg-Pro-Gly-Pro (C33H57N11O9, 751.9 g/mol, CAS 129954-34-3). It is supplied as a lyophilized powder for laboratory research.
How is Selank related to tuftsin?
Its first four residues, Thr-Lys-Pro-Arg, are the tuftsin sequence. Selank adds a Pro-Gly-Pro extension at the C-terminus.
What has Selank been studied for in research?
Published work covers its breakdown products in plasma, its inhibition of enkephalin-degrading enzymes in serum and plasma assays.
How should lyophilized Selank be stored?
Sealed vials are commonly kept frozen at around -20 C, protected from light and moisture. Letting a cold vial warm to room temperature before opening limits condensation.
Research use only. Not for human or veterinary use. This article summarises published laboratory research for informational purposes and is not medical advice.
References
- Nishioka K, Constantopoulos A, Satoh PS, Najjar VA. Biochem Biophys Res Commun. 1972;47(1):172-179. PMID: 4112769. DOI: 10.1016/s0006-291x(72)80025-1
- Zolotarev IuA, Dadaian AK, Dolotov OV, et al. Bioorg Khim. 2006;32(2):183-191. PMID: 16637290.
- Kost NV, Sokolov OIu, Gabaeva MV, et al. Bioorg Khim. 2001;27(3):180-183. PMID: 11443939. DOI: 10.1023/a:1011373002885
- Zolotarev IuA, Sokolov OIu, Kost NV, et al. Bioorg Khim. 2004;30(3):234-240. PMID: 15344652. DOI: 10.1023/b:rubi.0000030126.09208.c3
Compound data: PubChem CID 11765600 (Selank, https://pubchem.ncbi.nlm.nih.gov/compound/11765600).