The short version of TKPRPGP fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-02-24. Anything still debated is marked as such rather than presented as settled.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter notation. Its structure consists of the immunomodulatory tetrapeptide tuftsin, Thr-Lys-Pro-Arg, extended at the carboxyl terminus by a Pro-Gly-Pro segment. The molecular formula is commonly given as C33H57N11O9, corresponding to a monoisotopic mass near 751.4 Da and an average molecular mass near 751.9 Da. All seven residues are proteinogenic amino acids, and the molecule carries no modified side chains or non-natural linkages.
The compound was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences during the 1980s and 1990s. The stated design goal was to retain the immunomodulatory and central nervous system activity attributed to tuftsin while improving resistance to enzymatic breakdown. Adding a proline-rich tail to the short parent peptide was a deliberate strategy, because proline residues restrict the conformations available to many peptidases. The same laboratory produced Semax, an ACTH fragment analog, and both compounds were developed in parallel as short, enzymatically stabilized peptides intended for intranasal use.
Characterization of Selank in laboratory settings relies on standard peptide analytical techniques. Reverse-phase high-performance liquid chromatography separates the peptide from related impurities and degradation products, while mass spectrometry confirms molecular identity through accurate mass measurement. Amino acid analysis and peptide sequencing verify the primary structure when reference material is unavailable. Because Selank is a short chain, fragmentation-based analysis produces a diagnostic ion pattern that supports confident identification.
Peptide stability depends strongly on temperature, moisture, and pH. Lyophilized Selank is generally most stable when stored cold and dry, with freezer temperatures commonly used for long-term storage. In solution, the compound is susceptible to hydrolysis and to microbial growth if it is not handled aseptically. The C-terminal proline-rich extension appears to slow enzymatic cleavage relative to tuftsin, though quantitative degradation rates vary with the matrix and the conditions tested. Published stability data specific to Selank remain sparse.
Quality assessment of Selank samples typically combines purity determination with identity confirmation and counter-ion analysis. Purity is usually reported as a percentage by chromatographic area, with values above 95 percent often quoted for research-grade material. Water content and residual solvents are checked in lyophilized batches because they affect both stability and accurate mass determination. A reported purity figure does not by itself establish that a sample is the intended sequence, so orthogonal methods are needed to rule out sequence isomers or truncation products.
| Property | Value | Notes |
|---|---|---|
| Peptide sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Seven residues; tuftsin plus a Pro-Gly-Pro tail |
| Molecular formula | C33H57N11O9 | Commonly reported value for the free peptide |
| Monoisotopic mass | Roughly 751.4 Da | Average molecular mass near 751.9 Da |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Freely soluble in water | Also dissolves in saline and other polar solvents |
Pharmacokinetic data are sparse and largely derived from animal work. After intranasal administration the peptide appears in plasma within minutes, and reported half-lives are short, on the order of minutes to tens of minutes. Degradation proceeds through ordinary proteolytic cleavage into constituent amino acids and smaller fragments. Direct evidence that intact Selank reaches brain tissue in meaningful amounts is limited, and the extent of blood-brain barrier penetration is debated. Some authors argue that fragments, not the parent peptide, carry much of the observed activity.
Published clinical work is concentrated in Russian-language journals and generally involves small samples without independent replication. Systematic reviews in English note the shortage of randomised, placebo-controlled trials and the difficulty of verifying methods from translated reports. Outcome measures vary between studies, which complicates pooling of results. Interest in the compound as a cognitive or anxiolytic agent therefore rests on a thinner evidence base than the volume of citations suggests. Replication in well-powered trials with preregistered endpoints would be needed before firm conclusions about efficacy can be drawn.
Lyophilised material kept dry at minus 20 degrees Celsius or colder is the most stable form, and suppliers commonly state a shelf life of two years or more under those conditions. Once dissolved, degradation accelerates through hydrolysis and deamidation, particularly at alkaline pH or elevated temperature. Working solutions are usually divided into single-use aliquots to avoid repeated freeze-thaw cycles. The choice of reconstitution solvent affects both stability and the ionic strength of the final preparation.
Reverse-phase high-performance liquid chromatography with ultraviolet detection near 214 nanometres is the standard purity method. Mass spectrometry, typically electrospray ionisation, confirms identity through the expected mass-to-charge pattern. Amino acid analysis can verify composition independently. Chiral purity requires separate techniques such as derivatisation followed by chromatographic separation, and such data are rarely reported for research-grade material.
Quantification in biological matrices relies on liquid chromatography coupled to tandem mass spectrometry with stable-isotope internal standards. Low plasma concentrations and adsorption to container surfaces both complicate measurement. Solid-phase extraction is often needed to reduce matrix interference before injection. Reported limits of quantification differ widely between laboratories, which makes direct comparison of pharmacokinetic results difficult and limits meta-analysis.
Development work on the compound began in the 1980s and 1990s at the Institute of Molecular Genetics in Moscow, within the same research programme that produced the peptide Semax. Early investigators sought a tuftsin derivative with improved resistance to enzymatic breakdown and with activity in the central nervous system after peripheral administration. Most of the primary literature from this period was published in Russian, a factor that still shapes how easily the findings can be checked by outside groups.
Naming for this compound is not fully standardised in English sources. The spelling Selanc appears in some transliterations, and catalogue entries may instead list the peptide sequence itself as the identifier. Reference material sometimes groups it with other short synthetic peptides studied for behavioural effects, which can create confusion when citations are compared. Distinguishing the exact sequence from related tuftsin analogues is therefore a practical first step when reviewing any dataset or specification sheet.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, frequently abbreviated as TKPRPGP. It was designed as a structural analogue of tuftsin, a naturally occurring tetrapeptide released by enzymatic cleavage of the immunoglobulin heavy chain. The two additional proline residues at the C-terminal end extend the parent chain and change how the molecule behaves in solution. The free peptide has a calculated molecular mass of approximately 751.9 g/mol and is generally supplied as a lyophilised white to off-white powder.
Regulatory treatment varies by jurisdiction. In Russia the compound is a registered prescription product, while in the European Union and the United States it is generally handled as a research chemical without a marketing authorization. Suppliers therefore operate outside pharmaceutical oversight, and buyers rely on supplier documentation for purity and identity claims. Chain of custody and third-party testing are the main verification tools. Analysts note that the absence of a pharmacopoeial monograph for research-grade material limits standardization across vendors.
Purity assessment relies mainly on reverse-phase high-performance liquid chromatography with ultraviolet detection. Because the peptide lacks a strong chromophore, detection often uses backbone absorbance near 214 nm. Identity is confirmed by mass spectrometry, typically electrospray ionization or matrix-assisted laser desorption, comparing the measured mass against the expected value. Amino acid analysis can verify composition after acid hydrolysis. Diastereomer content and residual counterions are reported less often, although both can influence biological assays.
Lyophilized material is generally stable for extended periods when kept dry at or below minus twenty degrees Celsius. Working solutions are less stable, and common practice is to aliquot and freeze them so that repeated freeze-thaw cycles are avoided. Aqueous solutions are sensitive to pH extremes and to microbial growth, so short-term storage at refrigerator temperature is typical. Oxidation and hydrolysis are the principal degradation routes. Reconstitution with sterile water or a mild buffer is standard, and solutions should be protected from light.
== Limitations == Despite its aforementioned advantages as a specialized tool, the B1H system does have some drawbacks. First, the B1H selection system is limited in its capacity to determine the binding specificities of transcription factors with lengthy binding sites. This arises from the fact that the number of randomized “prey” clones required to represent all possible target sequences increases exponentially with the number of nucleotides in that target sequence. Second, some eukaryotic factors may not express or fold efficiently in the bacterial system, attributed to differing regulatory networks and transcriptional machinery. Hence when working with DNA-binding proteins of eukaryotic origin, a yeast-based hybrid system may be beneficial. Third, the B1H system may not be ideally suited for transcription factors that recognize binding sites with low affinity. The logic here is that competition created by binding sites elsewhere in the bacterial genome may limit the signal that can be realized from a single binding site that is present upstream of the reporter.
== Effects on Animals == Calciseptine has been examined in vivo and in vitro in all kinds of animals, but mostly in rats. Calciseptine relaxes precontracted rat (thoracic) aorta and decreases blood pressure drastically. The decrease in blood pressure shows a combination of short- and long-lasting effects. The early, acute onset took five minutes, and the effect could last for 120 minutes or longer. In addition, calciseptine had only a small effect on the heart rhythm, changing it only slightly. Furthermore, it can also relax the trachea rings in the lungs. These effects can be explained by the relaxing activity of calciseptine on various smooth muscle cells. The inhibitory effect of calciseptine results in a decreased or total disappearance of electric activity in these cells. The total inhibitory effect depends on the tissue: the cardiovascular system is the most vulnerable, while neuronal cells are less vulnerable and skeletal muscle cells are completely resistant. This difference in tissue sensitivity is probably caused by slight differences in the L-type calcium channels in these tissues. These effects can occur at low subjected amounts of 0.1 till 1 μM calciseptine. In mouse myotube the Ca2+ currents show higher amplitude after incubation in calciseptine (1 μM). This effect of calciseptine on the Ca2+ current develops relatively fast. Calciseptine changes the reversal potential of the Ca2+ current in mouse myotubes. In adult frog skeletal muscle fibers calciseptine also causes an increased Ca2+ current.
== Caspase-2-PIDDosome == Caspases are a family of cysteine proteases that play key roles in regulating apoptosis and inflammatory responses. These enzymes are divided into two main groups: initiator and executioner caspases, based on their structure and function. Initiator caspases, such as caspase-8 and caspase-9, become activated through the formation of large protein complexes, which promote dimerization and self-cleavage. Once activated, they initiate the activation of effector caspases, like caspase-3 and caspase-7, which then execute the final stages of programmed cell death. Caspase-2 has similar structure to the initiator caspase-9, particularly due to the presence of a caspase activation and recruitment domain (CARD). Its activation mechanism also involves dimerization, followed by autoprocessing, which is essential for its full activation. Similar to caspase-9 and its role within the apoptosome, the multiprotein complex that facilitates caspase-2 activation has been designated as the "PIDDosome" (Caspase-2-PIDDosome). This structure is formed by the C-terminal fragment of PIDD1 (p53-induced death domain protein 1) and RAIDD (receptor-interacting protein-associated ICH-1/CED-3 homolog with a death domain, also known as CRADD) in a 5:5 stoichiometric ratio. Two additional RAIDD molecules are positioned on top of the core complex, completing its assembly. RAIDD functions as a dual adaptor protein, featuring specialized domains that facilitate key interactions.
Sources: en.wikipedia.org
Ice-T finally landed a deal with a major label Sire Records. When label founder and president Seymour Stein heard his demo, he said Ice-T sounded like Bob Dylan. Shortly after, he released his debut album Rhyme Pays in 1987 supported by DJ Evil E, DJ Aladdin and producer Afrika Islam, who helped create the mainly party-oriented sound. The record wound up being certified gold by the Recording Industry Association of America. That same year, he recorded the title theme song for Dennis Hopper's Colors, a film about inner-city gang life in Los Angeles. His next album Power was released in 1988, under his own label Rhyme Syndicate, and it was a more assured and impressive record, earning him strong reviews and his second gold record. Released in 1989, The Iceberg/Freedom of Speech... Just Watch What You Say! established his popularity by matching excellent abrasive music with narrative and commentative lyrics. In the same year, he appeared on Hugh Harris' single "Alice". In 1991, he released his album O.G. Original Gangster. On OG, he introduced his heavy metal band Body Count in a track of the same name. Ice-T toured with Body Count on the first annual Lollapalooza concert tour in 1991, gaining him appeal among middle-class teenagers and fans of alternative music genres. The album Body Count was released in March 1992.
== Identification methods == Moonlighting proteins have usually been identified by chance because there is no clear procedure to identify secondary moonlighting functions. Despite such difficulties, the number of moonlighting proteins that have been discovered is rapidly increasing. Furthermore, moonlighting proteins appear to be abundant in all kingdoms of life. Various methods have been employed to determine a protein's function including secondary moonlighting functions. For example, the tissue, cellular, or subcellular distribution of a protein may provide hints as to the function. Real-time PCR is used to quantify mRNA and hence infer the presence or absence of a particular protein which is encoded by the mRNA within different cell types. Alternatively immunohistochemistry or mass spectrometry can be used to directly detect the presence of proteins and determine in which subcellular locations, cell types, and tissues a particular protein is expressed. Mass spectrometry may be used to detect proteins based on their mass-to-charge ratio. Because of alternative splicing and posttranslational modification, identification of proteins based on the mass of the parent ion alone is very difficult. However tandem mass spectrometry, in which each of the parent peaks is in turn fragmented, can be used to unambiguously identify proteins. Hence tandem mass spectrometry is one of the tools used in proteomics to identify the presence of proteins in different cell types or subcellular locations.
dry box A chamber or container in which the interior is maintained at very low humidity, often by filling it with argon or with air lacking carbon dioxide, in order to provide an inert atmosphere in which manipulation of very reactive chemicals or moisture-sensitive procedures can be carried out in the laboratory.
Epidermolysis bullosa dystrophica or dystrophic EB (DEB) is an inherited disease affecting the skin and other organs. "Butterfly child" is the colloquial name for children born with the disease, as their skin is seen to be as delicate and fragile as the wings of a butterfly.
Sources: en.wikipedia.org
The sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter code. It combines the tetrapeptide tuftsin with a carboxyl-terminal Pro-Gly-Pro extension. This full sequence identifies the molecule more precisely than the research name.
No peptide with this exact sequence has been identified as an endogenous substance. It is a laboratory-designed analog of tuftsin, a naturally occurring immunomodulatory tetrapeptide. The Pro-Gly-Pro extension has no known natural source.
Proline introduces conformational constraints that make a peptide less accessible to common peptidases. This is a standard stabilization strategy in peptide design. The added residues also increase the distance between the active tuftsin portion and typical cleavage sites.
The most common approach combines reverse-phase liquid chromatography with mass spectrometry. Chromatography separates the components while mass spectrometry confirms the molecular mass. Peptide sequencing or tandem mass analysis can further verify the amino acid order.