Selank

Molecular Identity and Classification

Selank is the synthetic heptapeptide L-threonyl-L-lysyl-L-prolyl-L-arginyl-L-prolyl-glycyl-L-proline, written H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH or, in one-letter code, TKPRPGP. It carries a free N-terminal amine and a free C-terminal carboxylic acid; neither terminus is acetylated or amidated. The molecular formula of the free base is C₃₃H₅₇N₁₁O₉, the average molecular weight 751.9 g/mol and the monoisotopic mass 751.4341 Da. The compound is registered under CAS number 129954-34-3 and appears in PubChem as compound 11765600, where it is also listed under the laboratory code TP-7 and the transliteration Selanc.

The full IUPAC name, (2S)-1-[2-[[(2S)-1-[(2S)-2-[[(2S)-1-[(2S)-6-amino-2-[[(2S,3R)-2-amino-3-hydroxybutanoyl]amino]hexanoyl]pyrrolidine-2-carbonyl]amino]-5-(diaminomethylideneamino)pentanoyl]pyrrolidine-2-carbonyl]amino]acetyl]pyrrolidine-2-carboxylic acid, reads from the C-terminal proline outwards and encodes seven defined stereocentres: two in threonine (2S,3R), one each in lysine, arginine and the three prolines (all 2S). Glycine, the only achiral residue, sits between the last two prolines.

Structurally, Selank is two modules joined head to tail. The N-terminal four residues are identical to tuftsin, Thr-Lys-Pro-Arg, first described by Najjar and Nishioka in 1970 and named after Tufts University; the sequence corresponds to residues 289–292 of the IgG heavy chain, in the CH2 domain of the Fc region, and is released from the immunoglobulin by sequential proteolytic cuts. The C-terminal three residues, Pro-Gly-Pro, belong to the glyprolines, the short proline- and glycine-rich peptides that Ashmarin and colleagues described as modules for stabilising and extending regulatory peptides. Selank is therefore a designed hybrid: a native regulatory sequence fused to a glyproline tail.

Selank was developed in Moscow at the Institute of Molecular Genetics of the Russian Academy of Sciences, the same group that produced Semax, a heptapeptide built on the identical design principle: Semax is the adrenocorticotropin fragment Met-Glu-His-Phe followed by Pro-Gly-Pro. The two peptides are frequently studied side by side precisely because they share a C-terminal tripeptide while differing completely in their N-terminal pharmacophores.

Structure and Chemical Features

Each residue contributes a specific chemical feature:

• Thr¹ supplies the free α-amine (pK_a roughly 8.5–9.5 for an N-terminal amine) and a secondary hydroxyl group on its β-carbon. The hydroxyl is the only alcohol in the molecule and acts as both hydrogen-bond donor and acceptor.
• Lys² carries a primary ε-amine at the end of a four-methylene side chain, pK_a near 10.5, protonated at all common laboratory pH values.
• Pro³, Pro⁵ and Pro⁷: three of the seven residues are proline, whose pyrrolidine ring closes onto its own backbone nitrogen. Each proline nitrogen is a tertiary amide nitrogen without an N–H.
• Arg⁴ carries a guanidinium group, pK_a about 12.5, the most basic group in the molecule and the dominant site of protonation in the gas phase.
• Gly⁶ has no side chain and gives the backbone between Pro⁵ and Pro⁷ its greatest local flexibility.

Charge and Polarity

With three basic groups (the N-terminal amine, the lysine ε-amine and the arginine guanidinium) against a single carboxylic acid, Selank is a strongly basic peptide. At pH 7 it carries a net charge of about +2: three positive charges and one negative charge. Calculation with standard side-chain and terminal pK_a sets places the isoelectric point near 11.5, between the lysine and arginine pK_a values; at pH 2, the conditions of a typical acidic HPLC mobile phase, all three bases are protonated and the carboxyl largely neutral, so the molecule carries close to +3. PubChem's computed descriptors underline how polar the peptide is: XLogP3 −6.1, topological polar surface area 322 Ų, 9 hydrogen-bond donors, 12 hydrogen-bond acceptors and 19 rotatable bonds across 53 heavy atoms.

Three X–Pro Bonds and Conformational Heterogeneity

The peptide bonds preceding each proline (Lys²–Pro³, Arg⁴–Pro⁵ and Gly⁶–Pro⁷) are tertiary amides. For ordinary secondary amides the trans geometry is strongly favoured, but across an X–Pro bond the cis/trans energy difference is small, so a measurable cis population persists in solution and the isomers interconvert slowly, on a timescale of seconds to minutes at room temperature, as reviewed by Wedemeyer, Welker and Scheraga. With three independent X–Pro bonds, Selank can in principle populate up to 2³ = 8 backbone isomers in slow exchange. For NMR this is the key structural fact: residues flanking the prolines give several sets of signals whose intensities report the isomer populations. The ring also restricts the proline φ dihedral angle to about −65°, which biases the Pro-Arg-Pro and Pro-Gly-Pro segments towards extended, polyproline II-like local conformations rather than compact turns.

Synthesis and Manufacturing Chemistry

Selank is prepared by solid-phase peptide synthesis (SPPS), introduced by Merrifield in 1963, with 9-fluorenylmethoxycarbonyl (Fmoc) α-amine protection of the kind described by Carpino and Han in 1972. Because the target is a C-terminal free acid ending in proline, the chain is built from the C-terminus on an acid-labile, sterically hindered resin, adding Gly, Pro, Arg, Pro, Lys and finally Thr. Three side chains need protection during the assembly: the threonine hydroxyl, the lysine ε-amine and the arginine guanidinium, each with an acid-labile group removed in the final cleavage step.

Three side reactions are specific to this sequence:

• Diketopiperazine formation at the dipeptide stage. After Gly is coupled to the resin-bound proline and its Fmoc group is removed, the free amine of H-Gly-Pro-resin can attack the ester linkage to the resin and cyclise into cyclo(Gly-Pro), cleaving the chain from the support. Gly–Pro and Pro–Pro C-terminal dipeptides are among the sequences most prone to this side reaction. The bulky trityl linker of 2-chlorotrityl resin, short deprotection times and immediate coupling of the third residue keep the loss small.
• Couplings onto secondary amines. Three acylations (Gly onto Pro⁷, Arg onto Pro⁵ and Lys onto Pro³) are made onto the less nucleophilic, more hindered secondary amine of proline. These steps are slower than couplings onto primary amines and benefit from stronger activation or double coupling; completeness is monitored with a test that detects secondary amines (for example the chloranil test), because the ninhydrin test reports primary amines.
• Arginine activation. An activated, side-chain-protected arginine derivative can cyclise to an unreactive δ-lactam, consuming reagent without extending the chain, which is a second reason for repeated coupling at Arg⁴; the sulfonyl-type side-chain group also needs a sufficiently long acid exposure at cleavage, with scavengers present to capture released cations.

A single acidic cleavage step releases the peptide from the support and removes all three side-chain protecting groups; the crude material is then precipitated, purified by preparative reversed-phase HPLC and lyophilized. Because the molecule carries three basic groups, it leaves purification as a salt with up to three counterions per peptide, and the trifluoroacetate introduced by HPLC is often exchanged for acetate — PubChem lists a diacetate form among its synonyms. Isotopically labelled material for tracer work has also been described: Shevchenko and co-workers reported tritium-labelled Selank in 2006.

Analytical Characterization

Reversed-Phase HPLC

Selank contains no tryptophan, tyrosine or phenylalanine, so it has essentially no absorbance at 280 nm. HPLC detection relies on the six amide bonds, which absorb in the 205–220 nm range; 214 nm is a common choice. With an XLogP3 of −6.1 and three positive charges in acidic eluent, the peptide is retained only weakly on C18 silica. Practical approaches include a shallow gradient beginning at very low organic content (for example 0–25% acetonitrile in water, both with 0.1% TFA, over 20–30 minutes), a polar-embedded or aqueous-stable C18 phase that tolerates fully aqueous starting conditions, or a more hydrophobic ion-pairing agent such as heptafluorobutyric acid, which pairs with each protonated base and increases retention markedly. Hydrophilic interaction chromatography (HILIC) is an orthogonal option for confirming purity. Mant and colleagues give a detailed account of how ion-pairing reagents and pH control the retention of basic peptides.

Peak shape deserves attention here. At low column temperatures the slowly interconverting cis/trans populations of a proline-rich peptide can give broadened or shouldered peaks that are not impurities; raising the column temperature (for example to 40–60 °C) accelerates isomerisation and sharpens the peak. Purity is reported as the percentage of total integrated UV area at the detection wavelength.

Mass Spectrometry and Expected Ions

In positive-mode electrospray ionisation, Selank's three basic sites make multiply charged ions prominent. The expected monoisotopic values, calculated from the elemental composition with a proton mass of 1.00728 Da, are:

• [M+H]⁺ at m/z 752.4413
• [M+2H]²⁺ at m/z 376.7243 (often the base peak under acidic conditions)
• [M+3H]³⁺ at m/z 251.4853

The first ¹³C isotope peak (M+1) is about 40% of the monoisotopic peak for a molecule with 33 carbons, so the isotope envelope of the 2+ ion shows peaks spaced by 0.5 m/z units, a quick check of charge-state assignment.

Tandem MS of Selank is governed by two well-characterised effects. First, cleavage of the amide bond on the N-terminal side of proline is strongly favoured (the "proline effect" documented by Breci and colleagues from a large database of peptide spectra). Selank has three such bonds, so the b₂/y₅, b₄/y₃ and b₆/y₁ pairs are expected to dominate. Second, the arginine guanidinium sequesters a proton, as described by the mobile-proton model of Wysocki and colleagues, so fragments that retain Arg⁴ carry charge preferentially. In practice the y₅ ion (PRPGP) and the b₄ ion (TKPR, the tuftsin sequence as an acylium/oxazolone ion) are the most diagnostic fragments.

Doubly charged fragments are also common for a peptide with this many basic sites; for example, y₆²⁺ appears at m/z 326.200 and y₅²⁺ at m/z 262.153. Proteolytic digestion is not needed (and not useful) for identity confirmation: the intact molecule is small, and its two basic residues are both followed by proline, the arrangement the classical Keil rule regards as trypsin-resistant.

Synthesis-related impurities of a peptide like this fall into a few predictable mass classes, and calculating them in advance makes an LC-MS impurity profile quick to read. Two features are specific to Selank. The des-Thr deletion peptide (KPRPGP) has exactly the composition of the y₆ fragment, so a signal at m/z 651.394 is a genuine impurity only if it elutes separately from the main peak; if it co-elutes, it is an in-source fragment. And because the sequence contains three prolines, a des-Pro impurity can arise at three positions that are isobaric (identical mass) and are distinguished only by retention time and by their MS/MS series.

Adduct ions are not impurities: sodium and potassium adducts of the intact peptide appear at m/z 774.423 ([M+Na]⁺) and 790.397 ([M+K]⁺), and should be read as such.

Peptide Content, Counterions and Composition

HPLC purity and peptide content answer different questions. Purity is the fraction of UV-absorbing material that is Selank; peptide content is the fraction of the weighed powder that is peptide at all, as opposed to counterions, bound water and residual salts. For a molecule with three basic groups, counterions are a large share of the mass. Taking 751.89 g/mol for the free base, 60.05 g/mol for acetic acid and 114.02 g/mol for trifluoroacetic acid:

Worked example: 10.0 mg of an otherwise dry diacetate salt contains 10.0 × 0.862 = 8.62 mg of free base, or 8.62 mg ÷ 751.89 g/mol = 11.5 µmol. Dissolved to 1.00 mL that is an 11.5 mM stock, not the 13.3 mM obtained by assuming pure free base; residual water lowers the figure further, which is why exact molar work relies on measured peptide content.

Amino-acid analysis after acid hydrolysis is the classical way to measure peptide content and to confirm composition; for Selank the expected molar ratio is Thr:Lys:Pro:Arg:Gly = 1:1:3:1:1. Proline is a secondary amine and reacts with ninhydrin to give a yellow product read at 440 nm rather than the purple product read at 570 nm, and threonine is partially destroyed during hydrolysis, so laboratories apply the usual correction factors. Ion chromatography quantifies acetate or trifluoroacetate, Karl Fischer titration measures water, and chiral analysis of the hydrolysate confirms that no D-isomers formed during synthesis.

Physicochemical Properties

Three cationic groups, almost no hydrophobic surface and a large polar surface make the peptide freely water-soluble and unlikely to aggregate or hold a stable secondary structure; the strongly negative partition coefficient means it does not cross lipid bilayers by passive diffusion to any meaningful degree, which matters when interpreting cell-based experiments.

Chemically, the peptide is robust. It contains none of the residues most often responsible for peptide degradation on storage: no methionine or cysteine to oxidise, no asparagine or glutamine to deamidate, no aspartate to isomerise, and no N-terminal glutamine to cyclise. Its residual chemical liabilities are acid- or base-catalysed amide hydrolysis under harsh conditions and, as for any peptide with a free N-terminal amine, the possibility of slow diketopiperazine formation from the first two residues in solution. That pathway is fastest when proline occupies position 2; in Selank proline sits at position 3, so it is expected to be minor, and its products would be cyclo(Thr-Lys) (229.143 Da) and the PRPGP pentapeptide ([M+H]⁺ 523.299, isobaric with the y₅ fragment). The lyophilized powder, like most peptide salts, is hygroscopic.

Research Context

The in vitro and membrane-level literature on Selank addresses three questions: what binds the tuftsin module, how the peptide interacts with peptide-degrading enzymes, and whether it alters ligand binding at GABA-A receptors.

The tuftsin module and its binding partners. Tuftsin was characterised as a stimulator of phagocytosis by leukocytes in cell-based assays, and Fridkin and Najjar's 1989 review covers its chemistry together with the large series of synthetic analogues prepared to map which positions tolerate substitution.

One binding partner is directly relevant to Selank's design: von Wronski and colleagues showed in 2006 that tuftsin, and still more strongly the pentapeptide analogue TKPPR, binds selectively to neuropilin-1, a cell-surface co-receptor, and competes with vascular endothelial growth factor for that site. Multimerised TKPPR had markedly higher affinity in competition-binding experiments. That work established TKP(P)R as a neuropilin-1-directed recognition element, which makes Selank's N-terminal module chemically interesting in its own right.

Interaction with peptide-degrading enzymes. Kost and co-workers measured the effect of Selank and of Semax on the enkephalin-degrading enzyme activity of human serum in 2001, reporting concentration-dependent inhibition with an IC₅₀ of about 20 µM for Selank and about 10 µM for Semax, both far more potent than puromycin or bacitracin in the same assay. They also found that pentapeptide fragments of both heptapeptides retained inhibitory activity while tri-, tetra- and hexapeptide fragments did not, a non-monotonic length dependence that argues against a simple effect of overall size or charge. Zolotarev and colleagues followed this in 2004 with a radiochemical assay using Leu-enkephalin labelled with tritium at every residue: after incubation with plasma, the labelled fragments were resolved by HPLC against unlabelled internal standards, apportioning several peptidase activities in one experiment. In plasma, aminopeptidases accounted for about 80% of Leu-enkephalin hydrolysis, dipeptidyl carboxypeptidases for about 10%, a carboxypeptidase pathway for about 6% and dipeptidyl aminopeptidases for about 2%. Bestatin predominantly inhibited the aminopeptidase and carboxypeptidase activities, whereas Selank was more specific for the carboxypeptidase and dipeptidyl carboxypeptidase activities. Together these papers define Selank as a weak, class-selective peptidase modulator in the micromolar range, and they are a reminder that in serum-containing media the peptide can perturb the proteolytic environment of an assay as well as being a substrate of it.

Ligand binding at GABA-A receptors. Vyunova and co-workers used radioligand binding to isolated brain plasma-membrane preparations to ask whether Selank changes the binding of tritiated GABA to its receptors. They reported that Selank behaves as a positive allosteric modulator of [³H]GABA binding, with effects that were subtype-selective and concentration-dependent, and that combining Selank with benzodiazepine-site ligands gave a response that was neither additive nor identical to either compound alone, implying binding sites that are distinct but may partially overlap. This is a membrane-level measurement of ligand occupancy rather than a functional electrophysiological one, so it constrains where the peptide can act without defining a channel-level mechanism; extending it means pairing saturation and competition binding (varying [³H]GABA to separate K_d from B_max changes) with recombinant subtype panels.

Transcript-level work in cultured cells. Filatova and colleagues applied Selank to IMR-32 neuroblastoma cells in culture and quantified 84 transcripts of the GABAergic and broader neurotransmission machinery by qPCR. Selank alone changed none of the mRNA levels measured. Co-incubation with GABA largely suppressed the changes that GABA produced on its own, and co-incubation with a second, multi-receptor reference ligand increased the number of transcripts that ligand altered. The negative result for Selank alone is as informative as the positive ones: in this model the peptide is not a transcriptional agent in its own right, and its measurable effect is on how the cells respond to another ligand.

Proteolytic logic of the glyproline tail. The chemical reason for appending Pro-Gly-Pro to tuftsin can be stated without reference to any organism. Most aminopeptidases and trypsin-like endopeptidases are poor at cleaving bonds in which proline occupies the position after the scissile bond, and in Selank both basic residues, Lys² and Arg⁴, are immediately followed by proline. Trypsin cleaves C-terminal to lysine and arginine, and the classical Keil rule holds that it does not cleave when proline follows. Rodriguez and colleagues re-examined that rule across 14.5 million tandem mass spectra and found a surprisingly large number of cleavages before proline, so Lys–Pro and Arg–Pro bonds are better described as slow trypsin substrates than as immune ones. A C-terminal proline is likewise a poor substrate for the classical carboxypeptidases, and bonds involving proline are handled mainly by a specialised set of proline-specific peptidases (prolyl oligopeptidase, dipeptidyl peptidase IV, aminopeptidase P and related enzymes). Selank is thus a textbook illustration of a general principle in peptide chemistry reviewed by Vanhoof and colleagues: inserting proline next to a cleavage site converts a generic substrate into one that only a narrow set of enzymes can process. At the bench this predicts which commercial proteases are unsuitable for mapping the peptide and which fragments partial degradation is likely to give (TKP, TKPR and PRPGP, calculated [M+H]⁺ at m/z 345.213, 501.314 and 523.299).

Typical in vitro designs. The one well-defined potency in the literature is the micromolar IC₅₀ in serum enzyme assays, so concentration-response series spanning that value by several log units in both directions are the natural starting point. The informative controls are a scrambled heptapeptide of identical composition, the parent tetrapeptide tuftsin, the free Pro-Gly-Pro tripeptide and a counterion-matched vehicle. Because the peptide is a peptidase substrate as well as a modulator, LC-MS sampling to confirm that intact Selank survives the incubation belongs in the design.

Comparison With Related Peptides

The Selank/Semax pair is especially useful analytically. Both are heptapeptides ending in Pro-Gly-Pro, both are free acids, and both are assembled by the same chemistry, yet they differ sharply in the properties an analyst measures. Semax contains histidine and phenylalanine, and a methionine thioether that can oxidise to the sulfoxide (a +16 Da satellite peak used as a quality marker). Selank has no aromatic residue and no oxidisable side chain at all, but carries three basic groups instead of Semax's one, which is why it elutes earlier on C18 and gives a more prominent 2+ ion by electrospray.

Laboratory Handling and Storage

Storing the solid. Lyophilized Selank is best kept tightly closed at −20 °C or colder, protected from light and moisture. The salt is hygroscopic: let a cold container reach room temperature in a desiccator before opening it, so that moisture does not condense on the powder and inflate the weighed mass.

Preparing solutions. Selank dissolves readily in high-purity water and common aqueous buffers; no organic co-solvent is needed. For accurate molar concentrations, correct the weighed mass for peptide content, as the salt table above illustrates. Stock solutions are commonly made at 1–10 mM, filtered through a 0.22 µm low-binding membrane when destined for cell culture, divided into single-use aliquots and frozen at −20 °C or −80 °C. Repeated freeze-thaw cycles should be avoided. Although the peptide itself is basic, its trifluoroacetate or acetate salt gives a mildly acidic solution in unbuffered water, so check the pH of a concentrated stock before adding it to a sensitive buffer.

Stability considerations. Selank is not subject to oxidation or deamidation; its liabilities are enzymatic and physical. Serum- or lysate-containing media carry prolyl peptidases and carboxypeptidases able to process proline-rich sequences, and strongly alkaline conditions promote slow amide hydrolysis. Solutions for long storage are better frozen than refrigerated, and long incubations in biological media are worth checking by LC-MS.

Adsorption and recovery. At low micromolar and sub-micromolar concentrations, polycationic peptides adsorb to negatively charged surfaces, bare glass included. Low-binding polypropylene labware and, where the design allows, a carrier protein in the assay buffer reduce the losses. Counterions deserve a matched control: Cornish and colleagues showed that trifluoroacetate alone can alter cell proliferation in culture, so the right comparator for a TFA salt is a vehicle at the same trifluoroacetate concentration.

Verification after storage. A short LC-MS run on a diluted stock, looking for the 2+ ion at m/z 376.72 and the absence of the fragment masses listed above, confirms identity and integrity. Each lot's certificate of analysis, shown live on this page, records the analytical results for the material on sale.

Frequently Asked Research Questions

What is Selank, chemically?

Selank is the synthetic heptapeptide H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH (TKPRPGP), molecular formula C₃₃H₅₇N₁₁O₉, average molecular weight 751.9 g/mol, monoisotopic mass 751.4341 Da. It is the tetrapeptide tuftsin extended at its C-terminus by the glyproline tripeptide Pro-Gly-Pro.

What is the CAS number of Selank?

Selank is registered under CAS number 129954-34-3 and appears in PubChem as compound 11765600, where it is also indexed under the code TP-7. Catalogue entries that give 29954-34-3 have dropped the leading digit of the registry number.

How does Selank differ from tuftsin?

Tuftsin is the tetrapeptide Thr-Lys-Pro-Arg (C₂₁H₄₀N₈O₆, 500.6 g/mol) found at residues 289–292 of the IgG heavy chain. Selank is that sequence with Pro-Gly-Pro appended, adding 251.3 g/mol and placing a proline immediately after the arginine, which turns the Arg–X bond into an Arg–Pro bond that trypsin-like enzymes cleave only slowly.

What masses should Selank show by mass spectrometry?

In positive-mode electrospray the calculated ions are [M+H]⁺ at m/z 752.441, [M+2H]²⁺ at m/z 376.724 and [M+3H]³⁺ at m/z 251.485. The 2+ ion is usually the most intense under acidic conditions because the peptide has three basic sites.

Which fragment ions are diagnostic in tandem MS?

Cleavage N-terminal to proline dominates, so the b₂/y₅, b₄/y₃ and b₆/y₁ pairs are expected: b₄ (TKPR) at m/z 483.304 and y₅ (PRPGP) at m/z 523.299 are the most useful, the latter also favoured because it retains the arginine that sequesters the charge.

Why is Selank hard to retain on a C18 column?

It has no aromatic or large aliphatic side chains, a computed XLogP3 of −6.1 and three protonated basic groups in acidic eluent, so it is very weakly retained by reversed-phase silica. A gradient starting at or near 0% organic, an aqueous-compatible or polar-embedded column, a stronger ion-pairing acid such as heptafluorobutyric acid, or an orthogonal HILIC method all improve the separation. Detect at 205–220 nm (214 nm is common): with no tryptophan, tyrosine or phenylalanine, the peptide has no 280 nm band.

Why do NMR spectra of Selank show more signals than expected?

Three of the six peptide bonds precede a proline and are tertiary amides whose cis and trans forms interconvert slowly. With three such bonds the molecule can populate up to eight slowly exchanging backbone isomers, so residues flanking the prolines give multiple sets of resonances. Variable-temperature experiments help assign them.

What is the difference between purity and peptide content for this peptide?

HPLC purity is the fraction of UV-absorbing material that is Selank. Peptide content is the fraction of the weighed powder that is peptide rather than counterion, water or salt. With three basic groups, a fully loaded trifluoroacetate salt is only about 69% peptide by mass and a diacetate about 86%, so a molarity calculated from gross weight can overstate the true value by roughly 15–45%.

What is the expected amino-acid analysis result?

Acid hydrolysis should give Thr:Lys:Pro:Arg:Gly in a molar ratio of 1:1:3:1:1. Proline is quantified at 440 nm rather than 570 nm in ninhydrin-based systems because it is a secondary amine, and threonine is partially lost during hydrolysis, so standard correction factors apply.

What is Selank's isoelectric point and net charge?

Calculated from standard pK_a values, the isoelectric point is near 11.5 and the net charge is about +2 at pH 7, rising towards +3 in an acidic HPLC mobile phase. The three basic groups are the N-terminal amine, the lysine ε-amine and the arginine guanidinium, against a single C-terminal carboxylate.

What in vitro systems appear in the Selank literature?

Published biochemical work includes enkephalin-degrading enzyme assays in human serum and plasma, radioligand binding of tritiated GABA to isolated brain plasma-membrane preparations, qPCR transcript panels in the IMR-32 neuroblastoma cell line, and binding studies of the tuftsin module to neuropilin-1. Full citations are listed below.

Where can I see the purity of the Selank I am buying?

This page shows the lot number, recorded purity and verified quantity of the lot currently on sale, taken live from the shop's lot-tracking database, together with that lot's certificate of analysis.

Sources & Further Reading

1. National Center for Biotechnology Information. PubChem Compound Summary for CID 11765600, Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro). PubChem CID 11765600.
2. Najjar VA, Nishioka K. 'Tuftsin': a natural phagocytosis stimulating peptide. Nature 1970;228(5272):672–673. doi:10.1038/228672a0
3. Fridkin M, Najjar VA. Tuftsin: its chemistry, biology, and clinical potential. Critical Reviews in Biochemistry and Molecular Biology 1989;24(1):1–40. doi:10.3109/10409238909082550
4. von Wronski MA, Raju N, Pillai R, et al. Tuftsin binds neuropilin-1 through a sequence similar to that encoded by exon 8 of vascular endothelial growth factor. Journal of Biological Chemistry 2006;281(9):5702–5710. doi:10.1074/jbc.M511941200
5. Kost NV, Sokolov OY, Gabaeva MV, Grivennikov IA, Andreeva LA, Myasoedov NF, Zozulya AA. Semax and Selank inhibit the enkephalin-degrading enzymes of human serum. Russian Journal of Bioorganic Chemistry 2001;27(3):156–159. doi:10.1023/A:1011373002885
6. Zolotarev YA, Sokolov OY, Kost NV, Vaskovsky BV, Myasoedov NF, Zozulya AA. Leu-enkephalin generally labeled with tritium in studying the Selank inhibiting effect on the enkephalin-degrading enzymes of human blood plasma. Russian Journal of Bioorganic Chemistry 2004;30(3):207–212. doi:10.1023/B:RUBI.0000030126.09208.c3
7. Vyunova TV, Andreeva L, Shevchenko K, Myasoedov N. Peptide-based anxiolytics: the molecular aspects of heptapeptide Selank biological activity. Protein & Peptide Letters 2018;25(10):914–923. doi:10.2174/0929866525666180925144642
8. Filatova E, Kasian A, Kolomin T, Rybalkina E, Alieva A, Andreeva L, Limborska S, Myasoedov N, Pavlova G, Slominsky P, Shadrina M. GABA, Selank, and olanzapine affect the expression of genes involved in GABAergic neurotransmission in IMR-32 cells. Frontiers in Pharmacology 2017;8:89. doi:10.3389/fphar.2017.00089
9. Ashmarin IP. Glyprolines in regulatory tripeptides. Neurochemical Journal 2007;1(3):173–175. doi:10.1134/S1819712407030014
10. Shevchenko VP, Nagaev IY, Alfeeva LY, Andreeva LA, Shevchenko KV, Myasoedov NF. Synthesis of tritium-labeled Selank. Radiochemistry 2006;48(3):296–300. doi:10.1134/S1066362206030167
11. Vanhoof G, Goossens F, De Meester I, Hendriks D, Scharpé S. Proline motifs in peptides and their biological processing. The FASEB Journal 1995;9(9):736–744. doi:10.1096/fasebj.9.9.7601338
12. Rodriguez J, Gupta N, Smith RD, Pevzner PA. Does trypsin cut before proline? Journal of Proteome Research 2008;7(1):300–305. doi:10.1021/pr0705035
13. Merrifield RB. Solid phase peptide synthesis. I. The synthesis of a tetrapeptide. Journal of the American Chemical Society 1963;85(14):2149–2154. doi:10.1021/ja00897a025
14. Carpino LA, Han GY. 9-Fluorenylmethoxycarbonyl amino-protecting group. The Journal of Organic Chemistry 1972;37(22):3404–3409. doi:10.1021/jo00795a005
15. Wedemeyer WJ, Welker E, Scheraga HA. Proline cis–trans isomerization and protein folding. Biochemistry 2002;41(50):14637–14644. doi:10.1021/bi020574b
16. Breci LA, Tabb DL, Yates JR, Wysocki VH. Cleavage N-terminal to proline: analysis of a database of peptide tandem mass spectra. Analytical Chemistry 2003;75(9):1963–1971. doi:10.1021/ac026359i
17. Wysocki VH, Tsaprailis G, Smith LL, Breci LA. Mobile and localized protons: a framework for understanding peptide dissociation. Journal of Mass Spectrometry 2000;35(12):1399–1406. doi:10.1002/1096-9888(200012)35:12<1399::AID-JMS86>3.0.CO;2-R
18. Mant CT, Chen Y, Yan Z, et al. HPLC analysis and purification of peptides. Methods in Molecular Biology 2007;386:3–55. doi:10.1007/978-1-59745-430-8_1
19. Cornish J, Callon KE, Lin CQ, et al. Trifluoroacetate, a contaminant in purified proteins, inhibits proliferation of osteoblasts and chondrocytes. American Journal of Physiology-Endocrinology and Metabolism 1999;277(5):E779–E783. doi:10.1152/ajpendo.1999.277.5.E779

Last reviewed: October 22, 2026