If you have been reading about Pro-Gly-Pro and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-08-01. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Proposed mechanisms center on modulation of the GABA system, but no single molecular target has been confirmed. Rodent studies report changes in GABA-A receptor expression and in the turnover of serotonin, dopamine, and norepinephrine in several brain regions. Increases in brain-derived neurotrophic factor and its receptor have also been described after repeated administration. These findings come largely from animal models, and the degree to which they describe human neurochemistry remains an open question. The mechanism is best characterized as multi-system and not fully resolved.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic heptapeptide | Tuftsin analogue with a C-terminal Pro-Gly-Pro tail |
| Amino acid sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Abbreviated TKPRPGP in most catalogues |
| Molecular mass | About 752 Da | Value for the free peptide |
| Solubility | Freely soluble in water | Aqueous solutions are kept cold and used promptly |
| Typical storage | -20 °C, dry, protected from light | Applies to the lyophilised powder before reconstitution |
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.
=== English === Order, Sons of St. George - Organized after the Civil War by Englishmen in the anthracite coal-mining region of Pennsylvania to counter the Molly Maguires. The organization "took permanent shape" at Scranton in 1871. Membership was open to "Englishmen, their sons, and grandsons, wherever born". Beneficiary membership was limited to those between 18 and 50; those over 50 were allowed honorary membership. The Order required belief in a Supreme Being, reverence for the Holy Bible, and loyalty to one's adopted country. By 1896 the order had about 35,000 members in the United States, Canada, and Hawaii. Ritual based on the legend of St. George included a "language of words, signs and grips" that the member learned upon initiation which could identify him to other members of the order. The Orders emblem was St. George conquering the dragon. The system of sick benefits varied by the lodge and the inclination of members. There was also a funeral benefit for members and their wives and a benevolent fund for brethren and "any worthy Englishman in distress". Some lodges also provided physicians and medicine for sick members. There was also a female auxiliary, the Daughters of St. George, but it was not officially recognized by the Supreme Lodge. In 1923 the Order was accused of promoting pro-British propaganda in textbooks used in New York by a representative of Mayor John Francis Hylan. Sons of England Benevolent Society - Fraternal order for Canadians of English descent.
==== United Kingdom ==== In the United Kingdom, the three medical Royal Colleges (the Royal College of Physicians of London, the Royal College of Physicians of Edinburgh and the Royal College of Physicians and Surgeons of Glasgow) are responsible for setting curricula and training programmes through the Joint Royal Colleges Postgraduate Training Board (JRCPTB), although the process is monitored and accredited by the independent General Medical Council (which also maintains the specialist register). Doctors who have completed medical school spend two years in foundation training completing a basic postgraduate curriculum. After two years of Core Medical Training (CT1/CT2), or three years of Internal Medicine Training (IMT1/IMT2/IMT3) as of 2019, since and attaining the Membership of the Royal College of Physicians, physicians commit to one of the medical specialties:
In the 1950s, Har Gobind Khorana and co-workers developed a phosphodiester method where 3'-O-acetylnucleoside-5'-O-phosphate 2 (Scheme 3) was activated with N,N'-dicyclohexylcarbodiimide (DCC) or 4-toluenesulfonyl chloride (Ts-Cl). The activated species were reacted with a 5'-O-protected nucleoside 1 to give a protected dinucleoside monophosphate 3. Upon the removal of 3'-O-acetyl group using base-catalyzed hydrolysis, further chain elongation was carried out. Following this methodology, sets of tri- and tetradeoxyribonucleotides were synthesized and were enzymatically converted to longer oligonucleotides, which allowed elucidation of the genetic code. The major limitation of the phosphodiester method consisted in the formation of pyrophosphate oligomers and oligonucleotides branched at the internucleosidic phosphate. The method seems to be a step back from the more selective chemistry described earlier; however, at that time, most phosphate-protecting groups available now had not yet been introduced. The lack of the convenient protection strategy necessitated taking a retreat to a slower and less selective chemistry to achieve the ultimate goal of the study.
Sources: en.wikipedia.org
== History == The efficacy of allogeneic cultured keratinocytes and fibroblasts in bovine collagen (Gintuit) was evaluated in two clinical studies in adults with insufficient gingival tissue. In each of the two studies, Gintuit was associated with an increase of at least 2 mm of gingival tissue in at least 50% of the study subjects. The overall clinical trial safety data for Gintuit included 121 subjects from both studies.
Laidlaw stated that reasons behind the cancellation included the fact that headcrabs and zombies "were pretty much played out at the time", and that the fact that it had to take place chronologically prior to Half-Life 2: Episode Two was too creatively constraining. Footage of the project was shown in a 2020 documentary by media company Noclip titled The Untold History of Arkane.
Sorbinil (INN) is an aldose reductase inhibitor being investigated for treatment of diabetic complications including neuropathy and retinopathy. Aldose reductase is an enzyme present in lens and brain that removes excess glucose by converting it to sorbitol. Sorbitol accumulation can lead to the development of cataracts in the lens and neuropathy in peripheral nerves. Sorbinil has been shown to inhibit aldose reductase in human brain and placenta and calf and rat lens. Sorbinil reduced sorbitol accumulation in rat lens and sciatic nerve of diabetic rats orally administered 0.25 mg/kg sorbinil.
Sources: en.wikipedia.org
North American box turtles breathe continuously during locomotion, and the ventilation cycle is not coordinated with the limb movements. This is because they use their abdominal muscles to breathe during locomotion. The last species to have been studied is the red-eared slider, which also breathes during locomotion, but takes smaller breaths during locomotion than during small pauses between locomotor bouts, indicating that there may be mechanical interference between the limb movements and the breathing apparatus. Box turtles have also been observed to breathe while completely sealed up inside their shells.
=== Environmental exposure === Formaldehyde and its adducts are ubiquitous in nature. Food may contain formaldehyde at levels 1–100 mg/kg. Formaldehyde, formed in the metabolism of the amino acids serine and threonine, is found in the bloodstream of humans and other primates at concentrations of approximately 50 micromolar. Even in animals that were deliberately exposed to formaldehyde, most formaldehyde-DNA adducts found in non-respiratory tissues derive from endogenously produced formaldehyde. Formaldehyde does not accumulate in the environment. It is broken down within a few hours by sunlight or by bacteria in soil or water. Humans metabolize formaldehyde quickly, converting it to formic acid. It nonetheless presents significant health concerns as a contaminant.
== Research == Her achievements include the discovery of adaptins, which are specific proteins that manage cell-trafficking to ensure the correct cell cargo is transported to the right location. She also discovered different combinations of adapting, when together with clathrin, form a coat around vesicles that bud from intracellular membranes and act as transporters for protein packages to be distributed in the cell. She also developed the technique "knock sideways," which inactivates proteins in seconds. After finishing her postdoc, she was able to start her own lab. Her main focus was to learn more about the AP protein in depth. She had to also work with DNA because in order to characterize the complexes thoroughly, she needed to clone the subunits. Robinson and her lab managed to find another AP complex, AP-3, which interacts with lysosomal membrane proteins such as LAMP1. AP-3 also interacts with tyrosinase, which is a key enzyme in melanin biosynthesis, so AP-3 is important for tyrosinase trafficking to premelanosomes. As of 2016 Robinson has a lab at Cambridge Institute for Medical Research. She specifically works with coated vesicles. The best-characterized coated vesicles are the clathrin-coated vesicles (CCVs). The coats on CCVs are primarily of clathrin, adaptor protein (AP) complexes, and alternative adaptors. Her working hypothesis is that for each trafficking pathway, there are a number of different adaptors, each of which is recruited independently onto the appropriate membrane.
Sources: en.wikipedia.org
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.
Tuftsin is a natural tetrapeptide derived from the Fc portion of immunoglobulin G. Selank retains that tetrapeptide at its N-terminus and adds three residues to improve resistance to enzymatic breakdown. The relationship is structural, and the two molecules are not interchangeable in experimental work.
It holds a product registration in Russia for intranasal use as an anxiolytic. Registrations of that kind are not automatically accepted by regulators elsewhere. In most other countries it is treated as an unapproved substance or a research material.
Reports describe effects on GABA-A receptor expression, monoamine turnover, and neurotrophic factor levels. These are proposed mechanisms drawn mainly from animal models. No single molecular target has been established.