Everything below concerns Pro-Gly-Pro. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its four N-terminal residues reproduce tuftsin, a tetrapeptide fragment of the immunoglobulin heavy chain, while the C-terminal Pro-Gly-Pro extension is a synthetic addition. The peptide has a molecular mass near 752 daltons and carries a net positive charge at physiological pH because of the arginine and lysine side chains. Published indexes list it under the name Selank and the sequence abbreviation TKPRPGP. Solid-phase peptide synthesis is the standard production route for research quantities.
Development took place at the Institute of Molecular Genetics of the Russian Academy of Sciences, where a series of short peptides were designed in the 1980s and 1990s. Selank was selected from variants of tuftsin that showed resistance to plasma peptidases. Russian regulatory approval covers it as an anxiolytic agent given intranasally. Outside that market the compound is normally handled as a research chemical rather than a medicine, and no widely recognised international pharmacopoeial monograph exists. The name Selank is a coined trade designation rather than a systematic chemical name.
Enzymatic stability motivates the extra three residues at the carboxyl end. Native tuftsin is cleaved quickly by circulating aminopeptidases and carboxypeptidases, which limits its duration of action and its usefulness as a tool compound. Extending the chain with proline-rich segments is a common design tactic because proline constrains the backbone and slows proteolysis. The same Pro-Gly-Pro motif appears in other Russian-developed peptides of the era. Whether the full seven-residue chain is required for activity, or whether it acts mainly as a prodrug releasing tuftsin, remains unresolved.
| 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 limited. Like most short peptides, Selank is vulnerable to plasma and tissue peptidases, and its measured half-life in circulation is short, on a minutes scale. The Pro-Gly-Pro tail slows this degradation but does not eliminate it. Intranasal administration is the route described in most reports, with absorption through the nasal mucosa and a hypothesized path into the central nervous system that avoids the blood-brain barrier. Direct measurements of human brain exposure are unavailable, so distribution claims rest on inference from animal work.
Clinical evidence comes mainly from small studies conducted in Russia, several of which were open-label or lacked robust blinding. Reported outcomes include lower anxiety scores, changes in attention measures, and effects on asthenic states following illness. Sample sizes are typically in the tens of participants, and independent replication outside the region is scarce. Reviews published in English generally note the limited methodological quality of the underlying trials. Whether the compound produces clinically meaningful effects under rigorous conditions remains unresolved.
Proposed mechanisms centre on the GABAergic system. Animal and tissue studies report changes in GABA-A receptor expression and reduced activity of GABA transaminase, the enzyme that degrades GABA. Effects on monoamine turnover, including serotonin and dopamine pathways, are also described, and a separate line of work links the peptide to increased expression of brain-derived neurotrophic factor in hippocampal tissue. Most of these findings come from rodent models and cell preparations. How the individual observations combine into a single coherent mode of action is not settled.
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.
Identity and purity of selank are established with reversed-phase high-performance liquid chromatography coupled to mass spectrometry. The peptide elutes from C18 columns with acetonitrile gradients in water containing trifluoroacetic acid or formic acid, and detection is usually performed by ultraviolet absorbance near 214 nm. Electrospray ionization in positive mode gives a doubly protonated ion near m/z 377, consistent with a mass of about 752 Da. Amino acid analysis or tandem mass spectrometry of fragment ions confirms the sequence. Because the molecule has no aromatic residues, it lacks a usable 280 nm chromophore, so low-wavelength detection or mass spectrometry is required.
Peptide bonds in selank are susceptible to hydrolysis under strongly acidic or basic conditions, and the terminal proline residues are vulnerable to exopeptidase activity in biological samples. Lyophilized powder stored dry at -20 °C typically remains stable for extended periods, whereas aqueous solutions degrade faster and may lose measurable purity within days to weeks depending on pH, temperature, and microbial load. Repeated freeze-thaw cycles promote aggregation and adsorption to container surfaces. For analytical work, solutions are usually prepared fresh, kept cold, and used within a single working day.
Handling follows standard practice for research peptides. Material is weighed in a low-humidity environment because the powder absorbs atmospheric moisture. Purity is reported as the percentage area of the main peak in a chromatogram, with specifications commonly set at 95 percent or higher; values below that threshold indicate the presence of truncated or modified species. Residual trifluoroacetate from purification is often present and may affect mass balance. Certificates of analysis should state the analytical method, the column and gradient used, and the lot-specific retention time so that results can be compared across suppliers.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed as a stabilized analogue of tuftsin, a naturally occurring tetrapeptide fragment derived from the immunoglobulin heavy chain. The additional Pro-Gly-Pro segment at the carboxyl terminus is intended to slow enzymatic cleavage. The compound is usually described in the literature as a synthetic peptide with anxiolytic and cognitive-related activity, a label that reflects a research context rather than an approved therapeutic category.
Most published work on selank originates from a small number of research groups in the Russian Federation. A large share of that record appears in Russian-language journals, which limits access for readers who rely on English-indexed databases. Independent replication by laboratories outside the original research network is sparse in publicly available sources. This concentration of origin and language is a frequently noted feature when the compound is summarized in broader reviews of synthetic peptides.
International cartels, such as OPEC, also exist. The Organisation for Economic Co-operation and Development (OECD) was founded as an economic-policy-focused organization. An example of a recently formed economic IGO is the Bank of the South. Educational organizations: Centered around tertiary-level study. EUCLID University was chartered as a university and umbrella organization dedicated to sustainable development in signatory countries. The United Nations has founded multiple universities, notably the United Nations University and the University for Peace, for research and education around issues relevant to the UN, such as peace and sustainable development. The United Nations also has a dedicated training arm: the United Nations Institute for Training and Research (UNITAR). Health and population organizations: Based on common perceived health and population goals. These are formed to address those challenges collectively, for example, the intergovernmental partnership for population and development Partners in Population and Development. Regional organizations: Open to members from a particular continent or other specific region of the world.
== Further reading == Nualart F, Rivas C, Montecinos V, Godoy A, Guaiquil V, Golde D, Vera J (2003). "Recycling of vitamin C by a bystander effect". J Biol Chem. 278 (12): 10128–33. doi:10.1074/jbc.M210686200. hdl:10533/174378. PMID 12435736.
=== Anticodon === An anticodon is a unit of three nucleotides corresponding to the three bases of an mRNA codon. Each tRNA has a distinct anticodon triplet sequence that can form 3 complementary base pairs to one or more codons for an amino acid. Some anticodons pair with more than one codon due to wobble base pairing. Frequently, the first nucleotide of the anticodon is one not found on mRNA: inosine, which can hydrogen bond to more than one base in the corresponding codon position. In genetic code, it is common for a single amino acid to be specified by all four third-position possibilities, or at least by both pyrimidines and purines; for example, the amino acid glycine is coded for by the codon sequences GGU, GGC, GGA, and GGG. Other modified nucleotides may also appear at the first anticodon position—sometimes known as the "wobble position"—resulting in subtle changes to the genetic code, as for example in mitochondria. The possibility of wobble bases reduces the number of tRNA types required: instead of 61 types with one for each sense codon of the standard genetic code), only 31 tRNAs are required to translate, unambiguously, all 61 sense codons.
Sources: en.wikipedia.org
Deionized water (DI water, DIW or de-ionized water), often synonymous with demineralized water/DM water, is water that has had almost all of its mineral ions removed, such as cations like sodium, calcium, iron, and copper, and anions such as chloride and sulfate. Deionization is a chemical process that uses specially manufactured ion-exchange resins, which exchange hydrogen and hydroxide ions for dissolved minerals, and then recombine to form water. Because most non-particulate water impurities are dissolved salts, deionization produces highly pure water that is generally similar to distilled water, with the advantage that the process is quicker and does not build up scale. However, deionization does not significantly remove uncharged organic molecules, viruses, or bacteria, except by incidental trapping in the resin. Specially made strong base anion resins can remove Gram-negative bacteria. Deionization can be done continuously and inexpensively using electrodeionization. Three types of deionization exist: co-current, counter-current, and mixed bed.
A linear series of three quadrupoles is known as a triple quadrupole mass spectrometer. The first (Q1) and third (Q3) quadrupoles act as mass filters, and the middle (q2) quadrupole is employed as a collision cell. This collision cell is an RF-only quadrupole (non-mass filtering) using Ar, He, or N2 gas (~10−3 Torr, ~30 eV) for collision induced dissociation of selected parent ion(s) from Q1. Subsequent fragments are passed through to Q3 where they may be filtered or fully scanned. This process allows for the study of fragments that are useful in structural elucidation by tandem mass spectrometry. For example, the Q1 may be set to 'filter' for a drug ion of known mass, which is fragmented in q2. The third quadrupole (Q3) can then be set to scan the entire m/z range, giving information on the intensities of the fragments. Thus, the structure of the original ion can be deduced. The arrangement of three quadrupoles was first developed by Jim Morrison of La Trobe University in Australia for the purpose of studying the photodissociation of gas-phase ions. The first triple-quadrupole mass spectrometer was developed at Michigan State University by Christie Enke and graduate student Richard Yost in the late 1970s. Quadrupoles can be used in hybrid mass spectrometers. For example, a sector instrument can be combined with a collision quadrupole and quadrupole mass analyzer to form a hybrid instrument.
== Medical uses == Selenium disulfide is sold as an antifungal agent in shampoos (such as Selsun Blue) for the treatment of dandruff and seborrheic dermatitis associated in the scalp with fungi of genus Malassezia. It is also used on the body to treat tinea versicolor (pityriasis versicolor), a type of fungal skin infection caused by a different species of Malassezia. A 2015 systematic review of topical treatments for seborrheic dermatitis of the scalp identified only a single randomized controlled trial evaluating selenium disulfide for the condition. It was a three-arm trial of 246 people with moderate to severe dandruff and compared treatment with 2% ketoconazole shampoo (n=97), 2.5% selenium disulfide shampoo (n=100), and placebo (shampoo base with no antiseborrheic agent) (n=49) for 29 days. The study found a 73% reduction in dandruff score with ketoconazole, a 67% reduction with selenium disulfide, and a 45% reduction with placebo. Based on the study, the systematic review concluded that selenium disulfide may be effective in the treatment of dandruff but that the available evidence is limited and overall evidence quality is low. It also found that while selenium disulfide has infrequent side effects, it seems to have more side effects than ketoconazole shampoo. Consequently, the review concluded that selenium disulfide should not be considered as a first-line therapy but instead should be used as an alternative treatment after other therapies like ketoconazole shampoo have proven not effective.
Denmark has low electricity costs (including costs for cleaner energy) in the EU, but general taxes (11.7 billion DKK in 2015) make the electricity price for households the highest in Europe. As of 2015, Denmark has no environmental tax on electricity. Denmark is a long-time leader in wind energy and a prominent exporter of Vestas and Siemens wind turbines, and in 2019 Denmark's exports of wind-turbine technology and services amounted to €8.9 billion. It has integrated fluctuating and less predictable energy sources such as wind power into the grid. Wind produced the equivalent of 43% of Denmark's total electricity consumption in 2017. The share of total energy production is smaller: In 2015, wind accounted for 5% of total Danish energy production. Energinet.dk is the Danish national transmission system operator for electricity and natural gas. The electricity grids of western Denmark and eastern Denmark were not connected until 2010 when the 600MW Great Belt Power Link went into operation. Cogeneration plants are the norm in Denmark, usually with district heating which serves almost 1.9 million households (January 1, 2025), 68% of all households. Waste-to-energy incinerators produce mostly heating and hot water. Vestforbrænding in Glostrup Municipality operates Denmark's largest incinerator, a cogeneration plant which supplies electricity to 80,000 households and heating equivalent to the consumption in 63,000 households (2016). Amager Bakke is an example of a new incinerator.
Sources: en.wikipedia.org
=== Sustained release === There are several methods by which tablets and capsules can be modified in order to allow for sustained release of the active compound as it passes through the digestive tract. One of the most common methods is to embed the active ingredient in an insoluble porous matrix, such that the dissolving drug must make its way out of the matrix before it can be absorbed. In other sustained release formulations the matrix swells to form a gel through which the drug exits. Another method by which sustained release is achieved is through an osmotic controlled-release oral delivery system, where the active compound is encased in a water-permeable membrane with a laser drilled hole at one end. As water passes through the membrane the drug is pushed out through the hole and into the digestive tract where it can be absorbed.
Mass cytometry is a high-dimensional single-cell analysis technique that integrates flow cytometry with time of flight mass spectrometry. It is used for the determination of the properties of cells (cytometry). In this approach, antibodies are conjugated with isotopically pure elements, and these antibodies are used to label cellular proteins. Cells are nebulized and sent through an argon plasma, which ionizes the metal-conjugated antibodies. The metal signals are then analyzed by a time-of-flight mass spectrometer. The approach overcomes limitations of spectral overlap in flow cytometry by utilizing discrete isotopes as a reporter system instead of traditional fluorophores which have broad emission spectra.
Cape Town ⟷ Kimberley ⟷ Johannesburg: General freight Durban ⟷ Richards Bay: Coastal freight Johannesburg ⟷ Durban: General freight (SA's busiest intermodal freight corridor) Johannesburg ⟷ Gqeberha / Ngqura: Automotive exports and manufactured goods Johannesburg ⟷ Polokwane: Mining supplies, and agricultural and manufacturing freight Johannesburg ⟷ Richards Bay: General freight Johannesburg ⟷ KuGompo City: Automotive and general freight Johannesburg ⟷ Komatipoort: Cross-border freight to Mozambique and the rest of the SADC Johannesburg ⟷ Beitbridge: Cross-border freight into Zimbabwe Johannesburg ⟷ Mahikeng / Ramatlabama: Cross-border freight into Botswana As of 2026, Transnet Freight Rail moves 17% of South Africa's freight annually, including 100% of its export coal and iron ore. The company coordinates its rail freight services with other Transnet divisions, such as ports, pipelines, and engineering. With over 25,000 employees, Transnet Freight Rail generates over R14 billion in annual revenue. For its 2025/2026 financial year, Transnet expected to transport a total rail cargo volume of around 168 million tons, up around 5%, from 160.1 million tons the year before. Under the South African Government's rail restructuring plan, the goal is for Transnet to reach a transport capacity of 185 million tons, with a further 65 million tons transported by private operators, by 2030. This would make for a total South African cargo rail capacity of 250 million tons per year.
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.
Selank is a seven-amino-acid peptide built from the tuftsin sequence plus a Pro-Gly-Pro tail. It is produced by chemical synthesis rather than extracted from a natural source. The free peptide is usually supplied as a lyophilised powder or in an aqueous formulation.