A practical reference on Peptidase stability: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-05-03 and is reviewed periodically as new material appears.
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.
Once dissolved, the peptide is markedly less stable than the dry powder. Aqueous solutions are subject to backbone hydrolysis and to microbial growth when they are handled without sterile technique. Buffered solutions near neutral pH are common for short-term laboratory work, while acidic conditions are sometimes used to improve solubility. Analytical laboratories generally prepare working solutions fresh rather than storing them, and a residual water film left in a reopened vial can seed degradation even when the container appears dry.
Reversed-phase high-performance liquid chromatography is the standard technique for estimating peptide purity. The result is a peak-area percentage, which describes how much of the detected material elutes as the main peak in one run. Mass spectrometry confirms the molecular mass and can reveal truncated, adducted, or otherwise modified species. Amino acid analysis or tandem mass spectrometry can address sequence fidelity when identity is in doubt. None of these measurements, taken alone, establishes that a sample is fit for any specific purpose.
Lyophilized selank is normally supplied as a dry powder and is considered stable for extended periods when kept cold and dry. Moisture uptake is the main practical threat, because absorbed water promotes both hydrolysis and aggregation in the solid state. Vials are usually warmed to room temperature before opening so that condensation does not form on the powder. Supplier documentation commonly specifies -20 °C for routine storage, with -80 °C used for material intended to be archived for years.
| 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 |
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.
Peptide bonds are vulnerable to protease attack, and Selank is no exception. Measured half-life in serum is short, on the order of minutes in several reports, which explains why intranasal administration is the common route described in the literature. Absorption across the nasal mucosa partially bypasses first-pass hepatic metabolism. Quantitative data on human bioavailability remain limited and are difficult to compare across studies.
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.
The primary structure of Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, corresponding to the molecular formula C33H57N11O9 and a monoisotopic mass of roughly 751.9 daltons. The N-terminal threonine and the arginine residue in the fourth position are shared with tuftsin, which carries the sequence Thr-Lys-Pro-Arg. The three additional residues at the C-terminus, Pro-Gly-Pro, extend the chain and are associated with greater resistance to enzymatic degradation. This extension also separates Selank from the shorter parent peptide.
Naming conventions place Selank in the same research family as Semax, another Russian-developed peptide investigated for cognitive effects. The two compounds share a lineage but differ in sequence and in the biological systems proposed as their targets. Semax descends from ACTH fragments, whereas Selank descends from tuftsin. Publications sometimes identify Selank by its full peptide sequence or by laboratory codes rather than one uniform trade name. Because replication outside Russia is limited, reports on its properties are best read alongside the study design and the purity of the material tested.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences as a structural analogue of tuftsin, a naturally occurring tetrapeptide fragment of the immunoglobulin heavy chain. The added Pro-Gly-Pro tail was intended to slow enzymatic degradation and extend biological activity. In Russia it is registered as an anxiolytic nasal preparation, while regulators elsewhere have not approved it for clinical use.
Proposed mechanisms centre on modulation of the GABAergic system, with reports of altered expression of genes related to GABA-A receptor subunits and changed monoamine turnover. Some studies describe inhibition of enkephalinase, the enzyme that degrades endogenous enkephalins, which may prolong opioid peptide signalling. Effects on brain-derived neurotrophic factor and on cytokine expression have also been reported. These findings come largely from animal models and small human studies, and the precise primary target remains unresolved.
Published clinical evidence is limited. Most controlled trials were conducted in Russia, enrolled modest numbers of participants, and appeared in Russian-language journals, which restricts independent verification. Reported outcomes include lower anxiety scores, improved attention and memory measures, and changes in fatigue ratings. Reviews written in English note methodological limitations such as small samples and inconsistent endpoints. Whether the compound produces clinically meaningful benefit relative to established anxiolytics is therefore an open question rather than an established finding.
== Pharmacokinetics == Loop diuretics are highly protein bound and therefore have a low volume of distribution. The protein bound nature of the loop diuretic molecules causes it to be secreted via several transporter molecules along the luminal wall of the proximal convoluted tubules to be able to exert its function. Loop diuretics usually have a ceiling effect whereby doses greater than a certain maximum amount will not increase the clinical effect of the drug. Also, there is a threshold minimum concentration of loop diuretics that needs to be achieved at the thick ascending limb to enable the onset of abrupt diuresis. The availability of furosemide is highly variable, ranging from 10% to 90%. The biological half-life of furosemide is limited by absorption from the gastrointestinal tract into the bloodstream. The apparent half-life of its excretion is higher than the apparent half-life of absorption via the oral route. Therefore, furosemide taken intravenously is twice as potent as an equivalent dose taken orally. However, for torsemide and bumetanide, their oral bioavailability is consistently higher than 90%. Torsemide has a longer half life in heart failure patients (6 hours) than furosemide (2.7 hours). A 40 mg dose of furosemide is clinically equivalent to a 20 mg dose of torsemide and to a 1 mg dose of bumetanide.
== Legal status == Sweden's public health agency suggested classifying 4-fluorobutyrylfentanyl as hazardous substance on August 18, 2014. In October 2015, 4-fluorobutyrylfentanyl became a controlled substance in China. 4-Fluorobutyrfentanyl is a Schedule I controlled drug in the USA since 1. February 2018.
=== Notable cases === Dan Christensen, painter of abstract art. Died due to heart failure caused by polymyositis. Robert Erickson, American composer and teacher who was a leading modernist exponent of "12-tone" composition. Died from the effects of polymyositis. Ana Estrada, the first person in Peru to die by euthanasia on 21 April 2024, at the age of 47. David Lean, film director. Eric Samuelsen, playwright. Victor Manuel Resendiz Ruiz, wrestler. Cardinal John Wright Rosita Velazquez, Puerto Rican actress and singer.
=== Anxiety === Lorazepam is used in the short-term management of severe anxiety. In the US, the Food and Drug Administration (FDA) advises against use of benzodiazepines such as lorazepam for longer than four weeks. It is fast-acting, and useful in treating fast-onset anxiety and panic attacks. Lorazepam can effectively reduce agitation and induce sleep, and the duration of effects from a single dose makes it an appropriate choice for the short-term treatment of insomnia, especially in the presence of severe anxiety or night terrors. It has a fairly short duration of action. Withdrawal symptoms, including rebound insomnia and rebound anxiety, may occur after seven days of use of lorazepam.
Sources: en.wikipedia.org
== In humans == There are many legends involving healing wounds by licking them or applying saliva. Saint Magdalena de Pazzi is said to have cured a nun of sores and scabs in 1589 by licking her limbs. The Roman Emperor Vespasian is said to have performed a healing of a blind man using his saliva. Pliny the Elder in his Natural History reported that a fasting woman's saliva is an effective cure for bloodshot eyes. In the Hebrew Bible saliva is associated with uncleanliness; however, in the Gospels there are three incidents where Jesus uses saliva to heal (Mark 7:33, Mark 8:23, John 9:6). Köstenberger suggests "by using saliva to cure a man, Jesus claims to possess unusual spiritual authority." There are potential health hazards in wound licking due to infection risk, especially in immunocompromised patients. Human saliva contains a wide variety of bacteria that are harmless in the mouth, but that may cause significant infection if introduced into a wound. A notable case was a diabetic man who licked his bleeding thumb following a minor bicycle accident, and subsequently had to have the thumb amputated after it became infected with Eikenella corrodens from his saliva.
==== Adverse effects ==== Cannabidiol use is associated with a reduction in appetite, diarrhoea, dry mouth, sedation and dizziness. These adverse events are mild and generally diminish with continued use. Additionally, an increased risk of blurred vision and interference with liver function with elevated levels of liver enzymes are reported. Due to potential liver injury, dose adjustment may be required in patients with liver diseases or taking other medications that interfere with the metabolism of cannabidiol.
=== Conservation === The Grhl gene family is tightly conserved between species across an estimated millions of years of evolution, also maintaining the binding site (AACCGGTT) on the target genes of Grhl. While the presence of the Grhl genes varies between species, the functions regulated remain largely analogous. The reason for the presence of multiple Grhl orthologues would likely be due to speciation and the evolution of species from a common ancestor over time. Due to many animals possessing Grhl genes, there are many possible animal models available for research on the Grhl family. At present, the most characterized are the models of Drosophila, mouse and zebrafish. Interestingly, Grh was also identified in fungi, which lack epidermal tissue and instead utilize a cell wall. This gives evidence that the formation of physical barriers across all, or a large variety of, species may have had an evolutionary ancestor that initially developed barrier formation as a result of the presence of a Grhl gene.
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.
Sealed, desiccated storage at -20 °C or colder is the standard recommendation for research-grade material. Vials should reach room temperature before they are opened, which limits condensation. Repeated temperature cycling is discouraged.