Quick answer
Selank is a synthetic heptapeptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro (about 751–752 Da), made by extending the immunomodulatory tetrapeptide tuftsin with a stabilizing Pro-Gly-Pro tail.
- Origin: tuftsin (Thr-Lys-Pro-Arg), a fragment of the immunoglobulin G heavy chain, plus a C-terminal Pro-Gly-Pro extension
- Mechanism status: described at the pathway level (GABAergic gene expression, enkephalin turnover, monoamine and cytokine readouts); no single receptor is universally accepted
- Typical model systems: rodent behavioral paradigms, brain-tissue expression profiling, immune cell cultures
- Handling: no Trp, Met or Cys residues, so it is chemically robust, but it still needs cold, dark, dry storage and a lot-specific certificate of analysis
- Material: available as lyophilized Selank research vials. For laboratory research use only; not for human consumption.
What Selank is
Selank is a short, fully synthetic peptide used by research laboratories as a probe of regulatory-peptide signaling. It has seven residues, a molecular mass of roughly 751–752 Da, and a sequence that is easy to state and easy to verify: Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues reproduce tuftsin, a naturally occurring tetrapeptide with immunomodulatory activity. The last three, Pro-Gly-Pro, were added so that the molecule survives long enough in biological media to be studied reproducibly. Selank is therefore best understood as an engineered analog: the biology of the parent sequence combined with a chemistry-driven stability fix. A shorter introduction is available in what is Selank peptide.
The compound sits in an unusual position among research peptides. It is not a ligand for a classical, well-mapped receptor in the way that GLP-1 analogs are, and it is not a growth-factor mimic. Instead it is discussed in terms of converging observations across several systems: expression of genes involved in GABAergic signaling, activity of enzymes that degrade enkephalins, monoamine turnover, and cytokine expression. That breadth is both what makes it interesting and what makes careful experimental language important. Throughout this guide, statements about Selank describe what has been observed in defined model systems, and where the evidence is hypothesis-level the text says so.
| Property | Selank |
|---|---|
| Class | Synthetic heptapeptide analog of tuftsin |
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Approximate molecular mass | 751–752 Da (theoretical average) |
| Parent peptide | Tuftsin, Thr-Lys-Pro-Arg (about 501 Da) |
| Stabilizing element | C-terminal Pro-Gly-Pro extension |
| Aromatic residues | None, so UV detection relies on the peptide bond near 214–220 nm |
| Supplied form | Lyophilized white powder |
Selank is most often discussed next to Semax, a peptide from the same research tradition that shares the Pro-Gly-Pro tail but derives from a different parent. The two are compared directly in Selank vs Semax: a research comparison, and a short summary appears in the related-compounds section below. This pillar guide consolidates what the library holds on Selank: its history, chemistry, proposed mechanisms, model-system findings, bench handling and quality documentation.
Discovery and history
Selank was developed by peptide-research groups in Russia as part of a systematic program to convert short regulatory peptides into stable, well-defined research tools. The strategy was fragment-based: identify a compact sequence with known biological relevance, then modify it so that it persists in solution and in biological media long enough for controlled experiments. This is different from discovering a wholly new receptor ligand. The starting chemistry was already known; the contribution was stabilization and experimental tractability.
The tuftsin template
Tuftsin was described in the late 1960s and early 1970s as a natural phagocytosis-stimulating peptide (see reference 1). Its sequence, Thr-Lys-Pro-Arg, corresponds to a short stretch of the immunoglobulin G heavy chain that is released by enzymatic cleavage. Tuftsin attracted interest because a four-residue fragment could influence immune-cell function, but it is rapidly broken down by peptidases, which limits its use as a reagent. Any assay that depends on the intact tetrapeptide has to contend with a very short functional window.
Extension with Pro-Gly-Pro
Appending Pro-Gly-Pro to the C-terminus gave a heptapeptide that resists the exopeptidase activity responsible for tuftsin's rapid loss. Proline-rich termini are a recurring motif in stabilized peptides because proline restricts backbone conformation and is a poor substrate for many peptidases. The same tripeptide appears in Semax, which is why the two compounds are described as products of one design philosophy even though their parent molecules differ: tuftsin for Selank, an ACTH fragment for Semax. The development story is also summarized in the Selank discovery and history article.
Reading the historical record
Terminology around "regulatory peptides" varies between older and regional literature, and some labels applied to Selank are broader than the evidence behind them. A useful habit is to separate three layers: the documented sequence, the model-system observations, and the interpretive labels attached afterwards. Historical interest does not establish a mechanism. When comparing papers, the questions that matter are which material was tested, in which model, with which endpoint, and whether an independent analytical method confirmed the identity of the peptide used.
Chemical structure and synthesis
Selank's chemistry is simple by peptide standards, and that simplicity is an advantage for analytical work. The sequence contains threonine, lysine, two prolines on either side of arginine, glycine and a third proline. It has two basic residues (Lys and Arg), which make the peptide strongly hydrophilic and positively charged at neutral pH, and it contains no tryptophan, methionine, cysteine or tyrosine, so the usual oxidation liabilities are absent.
Why the extension matters
Native tuftsin is about 501 Da; Selank is about 251 Da heavier, a difference that corresponds to the added Pro-Gly-Pro. That mass difference is a convenient identity check: if a lot shows a dominant species near 501 Da rather than 752 Da, the extension is missing and the material would behave like the short parent fragment, confounding stability or signaling experiments. The general logic of reading a modified sequence is covered in understanding amino acid sequences.
Solid-phase synthesis
Seven residues is well within the range that standard Fmoc solid-phase peptide synthesis handles with high fidelity. The chain is assembled residue by residue on a resin, cleaved and deprotected, then purified by reversed-phase chromatography. Proline-rich sequences can couple more slowly at some positions, so incomplete coupling can generate deletion products that closely resemble the target. Preparative HPLC removes truncated and deletion sequences, and the purified fractions are freeze-dried to a stable powder (see what is lyophilization).
Analytical confirmation
Identity and purity are established with two complementary methods. Reversed-phase HPLC resolves the main peak from related species; mass spectrometry checks that the dominant component has the expected mass. Neither alone proves every aspect of structure, so the two are read together. Because Selank has no aromatic side chains, detection relies on absorbance of the peptide bond at 214–220 nm rather than the 280 nm wavelength used for tryptophan- or tyrosine-containing peptides. Material attributes that do not appear in a purity percentage, such as counterion content, residual water and net peptide content, affect concentration calculations and should be recorded when lots are compared.
| Analytical question | Method | What a good result looks like |
|---|---|---|
| Is the intended sequence present? | Mass spectrometry | Dominant ion consistent with about 752 Da; no major species near 501 Da |
| How pure is the lot? | Reversed-phase HPLC at 214–220 nm | A single dominant peak with a real chromatogram attached |
| Are deletion or truncation products present? | HPLC plus MS of minor peaks | Minor peaks small and assignable |
| How much peptide is in the vial? | Net peptide content, water, counterion | Reported separately from chromatographic purity |
For a worked explanation of how to interpret these documents, see understanding HPLC purity.
Mechanism of action
The mechanism of Selank is an open question, and the most defensible summary is that it is a multi-pathway hypothesis rather than a single-receptor model. Reports involve several readouts that need not share one upstream cause. Collapsing them into one definitive mechanism would overstate what the data support. The details are also set out in the Selank mechanism of action article.
Tuftsin-derived and immunoregulatory signaling
Because Selank derives from tuftsin, immune readouts were a natural place to look. Cytokine expression in immune cell preparations has been examined, and the peptide is discussed as an immunoregulatory tool as well as a neuro-research tool. These observations are made under controlled assay conditions and describe how cells in culture respond, not what happens in an intact organism.
GABAergic gene expression
One of the better-documented lines of work reports that Selank changes the expression of genes involved in GABAergic neurotransmission in rodent brain tissue (reference 3). That is a transcriptional observation: it shows that a set of messenger RNAs changes after exposure to the peptide, not that the peptide binds a GABA receptor. Distinguishing direct binding from downstream regulation requires binding assays and receptor perturbation experiments.
Enkephalin turnover and monoamines
Other proposals include inhibition of enzymes that break down enkephalins, which would raise the persistence of endogenous opioid peptides in tissue, and altered turnover of monoamines such as serotonin and dopamine. These too are pathway-level observations from rodent tissue and cell studies. They are plausible partners to the gene-expression findings, but they have not been unified into a single accepted model.
Stability as part of the mechanism
The Pro-Gly-Pro extension is proposed to slow enzymatic degradation, giving the intact heptapeptide a usable window that tuftsin lacks. This has an experimental consequence: in any assay the intact peptide and its fragments may be present together, and they need not produce identical readouts. Time-course sampling and an analytical check of what remains intact are therefore part of good mechanistic design.
| Proposed pathway | Type of evidence | Main caveat |
|---|---|---|
| GABAergic gene expression | Transcript changes in rodent brain tissue | Expression change is not receptor binding |
| Enkephalin-degrading enzymes | Enzyme-activity and tissue measurements in models | Not integrated with other readouts |
| Monoamine turnover | Neurochemical measurements in rodents | Depends on region, timing and model |
| Cytokine expression | Immune cell cultures and tissue | Culture state and peptide stability confound results |
Designing mechanistic experiments
Useful designs pair a phenotype with a proximal molecular measurement, include an inactive-sequence or tuftsin-only comparator where possible, and sample at several time points so that early signaling can be separated from later transcriptional change. A predefined hypothesis, written before data collection about which result would support or contradict each pathway, is more informative than collecting many loosely connected endpoints and choosing a narrative afterwards.
Preclinical research findings
Published characterization of Selank is concentrated in neuroscience-oriented model systems, with a smaller body of work on immune readouts. Rodent models and cultured cells form the usual substrate. All of it describes model behavior under controlled conditions and is interpreted only within the system in which it was measured. A fuller summary is in the Selank preclinical research article.
| Model system | Typical readout | Interpretation note |
|---|---|---|
| Rodent behavioral paradigms | Anxiety-related behavioral tasks | Phenotype only; does not identify a molecular target |
| Rodent brain tissue | Gene-expression profiling, including GABAergic genes | Transcript level; needs protein or functional confirmation |
| Rodent tissue neurochemistry | Monoamine turnover, enkephalin-degrading enzyme activity | Region- and time-dependent |
| Immune cell cultures | Cytokine output | Sensitive to culture state and peptide stability |
| Comparative designs with Semax | Side-by-side readouts for two stabilized peptides | Helps separate effects of the tuftsin versus ACTH-derived core |
From phenotype to mechanism
Behavioral endpoints can identify a reproducible phenotype, but they do not establish the molecular target responsible. Stronger designs connect behavior with biochemical or expression readouts collected under matched conditions, then use pathway-selective controls to test competing explanations. This distinction is especially important for Selank because its mechanism is broader than a single receptor interaction.
Sources of variability
Animal strain, sex, age, handling, task design and environmental conditions can all change behavioral results. Cell studies add their own variables: culture state, peptide stability and sampling time. Transparent reporting and replication across independent models are therefore essential. Test-article identity and purity should be confirmed so that differences are not attributed to biology when they actually arise from material variation.
The value of negative findings
Null results are informative when assay sensitivity and peptide integrity are demonstrated. Reporting full time courses, complete control data and failed replications defines the boundaries of a model response and reduces selective interpretation of variable behavioral endpoints. The literature on Selank benefits from this more than most, because behavioral readouts are inherently noisy.
Handling, reconstitution and storage
Selank is one of the easier peptides to handle on the bench. The absence of tryptophan, methionine and cysteine removes the main oxidation pathways, and the two basic residues make it freely soluble in aqueous diluents. What remains are the generic risks that apply to any lyophilized peptide: moisture, temperature cycling, light, microbial contamination and adsorption to surfaces at low concentration. Compound-specific notes are in Selank reconstitution and storage; the step-by-step method is in the lyophilized-peptide reconstitution guide, and a fully worked example for a different compound is in how to reconstitute retatrutide step by step.
Preparing a stock solution
Allow the vial to reach room temperature before opening so condensation does not wet the cake. Use sterile technique and add bacteriostatic water slowly down the inside wall of the vial instead of onto the powder. Dissolve by swirling; vortexing and shaking are unnecessary and can foam the solution. The only quantitative decision is the diluent volume, because concentration is simply the mass in the vial divided by the volume added. The reconstitution calculator performs the arithmetic for any vial size.
| Vial contents | Diluent added | Stock concentration |
|---|---|---|
| 5 mg | 1 mL | 5 mg/mL |
| 5 mg | 2 mL | 2.5 mg/mL |
| 10 mg | 1 mL | 10 mg/mL |
| 10 mg | 2 mL | 5 mg/mL |
| 10 mg | 4 mL | 2.5 mg/mL |
Worked example: a 10 mg vial reconstituted with 2 mL gives 10 mg ÷ 2 mL = 5 mg/mL. A working solution at 0.5 mg/mL is then a tenfold dilution of that stock. These are illustrative concentration calculations for bench planning; actual assay concentrations are set by experimental design.
Storage
The lyophilized powder is the most stable form and should be kept cold, dry and protected from light until needed. Once in solution, keep the stock cold, label it with concentration and date, and avoid repeated freeze–thaw cycles by dividing it into small aliquots in low-bind tubes. Dilute solutions lose peptide to container surfaces, so working dilutions are best prepared fresh. General cold-chain principles are covered in storing research peptides. Matching handling procedures between Selank and Semax keeps cross-compound experiments comparable, noting that Semax has an oxidation-prone methionine that Selank lacks.
Purity, COA and quality
Reproducible work depends on knowing exactly what is in the vial. For Selank the relevant quality questions are short and answerable: is the full seven-residue sequence present, is the chromatographic purity supported by a real trace, and does the observed mass match the theoretical value? A lot-specific certificate of analysis should address all three, and batch documents are collected on the CoA page. The reading skills involved are explained in how to read a COA, and independent verification is discussed in third-party testing explained. Compound-specific checks are in Selank purity testing and identity verification.
- Match the lot number on the vial to the certificate of analysis
- Confirm the HPLC purity figure is backed by an actual chromatogram, not just a number
- Compare the observed mass with the theoretical value of about 752 Da
- Look for any species near 501 Da that would indicate loss of the extension
- Record the lot number, storage conditions and reconstitution date with the dataset
Keeping those details with the data lets an unexpected result be traced to the reagent and lets another laboratory repeat the work with equivalent material. Research-grade Selank is supplied as a lyophilized powder; buyers comparing suppliers can consult where to buy Selank for research for the documentation criteria to look for.
Related compounds and comparisons
The closest relative is Semax, which shares the Pro-Gly-Pro tail but derives from the ACTH(4-10) region rather than tuftsin. Selank is generally contrasted with it in terms of parent molecule and proposed pathways. The table summarizes the differences documented in the library.
| Feature | Selank | Semax |
|---|---|---|
| Parent sequence | Tuftsin, Thr-Lys-Pro-Arg | ACTH fragment, Met-Glu-His-Phe |
| Full sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Met-Glu-His-Phe-Pro-Gly-Pro |
| Approximate mass | About 752 Da | About 814 Da |
| Proposed pathways | GABAergic expression, enkephalin turnover, monoamines, cytokines | BDNF/TrkB expression, melanocortin-related signaling |
| Main handling liability | Few; no oxidation-prone residues | N-terminal methionine oxidation |
See Selank vs Semax for the full comparison, the Semax research overview for the ACTH-derived member of the pair, and N-acetyl Semax amidate vs Semax for a modified variant of that scaffold. The Selank product page lists current specifications.
Frequently asked questions
What is Selank derived from?
Selank is a synthetic heptapeptide based on tuftsin, the immunomodulatory tetrapeptide Thr-Lys-Pro-Arg, extended with a C-terminal Pro-Gly-Pro sequence for stability. The complete sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro.
What is the molecular mass of Selank?
The theoretical average mass is approximately 751–752 Da. Tuftsin alone is about 501 Da, so a difference of roughly 251 Da confirms that the extension is present.
Does Selank act through one established receptor?
No. It is generally discussed through pathway-level observations such as GABAergic gene expression, enkephalin-degrading enzymes, monoamine turnover and cytokine expression, rather than a single universally accepted receptor target.
What does the Pro-Gly-Pro extension do?
It slows cleavage by peptidases that rapidly degrade tuftsin, so the analog persists longer in biological media. The same tripeptide is used for the same purpose in Semax.
What model systems has Selank been examined in?
Rodent behavioral paradigms, brain-tissue gene-expression profiling, neurochemical measurements and immune cell cultures in which cytokine output is measured. Findings apply only to the model in which they were obtained.
How does Selank differ from Semax?
They share the Pro-Gly-Pro tail but derive from different parents: tuftsin for Selank and an ACTH fragment for Semax. Their proposed pathways and handling liabilities differ, notably Semax's oxidation-prone methionine.
How is Selank supplied and stored?
As a lyophilized powder kept cold, dry and dark. After reconstitution the stock should be labeled, kept cold and divided into aliquots to avoid repeated freeze–thaw cycles.
How is the stock concentration calculated?
Divide the peptide mass in the vial by the diluent volume added. For example, 10 mg in 2 mL gives 5 mg/mL. The reconstitution calculator on this site does the same arithmetic for other vial sizes.
Why is Selank not monitored at 280 nm?
Its sequence has no tryptophan or tyrosine, so there are no aromatic side chains. HPLC detection therefore relies on peptide-bond absorbance near 214–220 nm.
What documentation should accompany a lot?
A lot-specific certificate of analysis with HPLC purity backed by a chromatogram and a mass-spectrometry identity result, ideally corroborated by third-party testing.
Research-use statement
For laboratory research use only; not for human consumption. Everything in this guide describes laboratory observations in cells, tissues and animal models, together with analytical chemistry and bench handling. It is research education and not guidance for use in people or animals.
References
- Najjar VA, Nishioka K. Tuftsin: a natural phagocytosis stimulating peptide. Nature. 1970;228:672–673.
- Kolomin T, Shadrina M, Slominsky P, Limborska S, Myasoedov N. A new generation of drugs: synthetic peptides based on natural regulatory peptides. Neuroscience and Medicine. 2013;4:223–252.
- Volkova A, Shadrina M, Kolomin T, et al. Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Frontiers in Pharmacology. 2016;7:31.